Awgichew, Kassahun: Comparative performance evaluation of Horro and Menz sheep of Ethiopia under grazing and intensive feeding conditions

49

Chapter 4. RESULTS AND DISCUSSION

4.1 Lamb performance traits

4.1.1 Weight development from birth to weaning (90 days)

Lamb birth weight and ewe post partum body weight was recorded within 24 hours after birth. Lambs were weaned at about 90 days of age. Although ewes were synchronised before mating in order to have concentrated lambing events, lambings during the three lambing seasons were spread as follows: a) First Group (Dry'92) : 28.09. - 07.11.92; b) Second Group (Wet'93): 29.05 - 12.07.93; c) Third Group (Dry'93): 21.10. - 30.11.93. In all three seasons, the lambing time was spread over a period of 5-6 weeks. Due to lack of records, stillborn lambs were excluded from the analysis of birth weight.

Table 12 shows the Least Squares means of birth and other weights until weaning (90 days). Horro lambs had significantly heavier (p <0.001) birth weight than Menz lambs (2.43 ± 0.03 kg vs 2.17 ± 0.03 kg, respectively). Males were heavier (p <0.001) at birth compared to females weighing 2.38 ± 0.03 vs 2.22 ± 0.02 kg respectively. Single born lambs were heavier (P <0.001) at birth (2.59 ± 0.02 kg ) compared to twins (2.01 ± 0.03 kg). Lambs born from second parity ewes were also heavier (p <0.001) at birth than those born from ewes of first parity weighing 2.44 ± 0.03 kg and 2.16 ± 0.03 kg respectively.

Birth weights of lambs born in the three seasons (Dry season'92, Wet season'93 and Dry season'93) were 2.22 ± 0.04, 2.30±0.04 and 2.38 ± 0.04 respectively and were significantly different (p <0.05).

Lambs were weaned at about 90 days of age. To avoid a wide gap between weaning ages, lambs were weaned in two batches so that the majority of lambs are weaned at 90 ± 15 days of age.

Menz and Horro lambs did not differ significantly (p >0.05) in weaning weight at 90 days of age (8.03 ± 0.14 vs 8.22 ± 0.16 kg respectively). Males were significantly heavier (P <0.05) than females at weaning weighing 8.29 ± 0.14 and 7.96 ± 0.14 kg respectively.


50

Birth type has also influenced weaning weight significantly (p <0.001) as shown in Table 12 where single born lambs have maintained their weight superiority to weaning and beyond. Second parity ewes had also significantly heavier lambs at weaning (8.72 ± 0.13) compared to those born to first time lambers (7.53 ± 0.15) indicating the influence of relatively heavier and older ewes reflected probably through higher milk yield on pre-weaning lamb body weight. Lambs born in the third lambing season did not maintain their superiority in birth weight at all stages of growth (Table 12). Weaning weights of lambs born in the three seasons were 8.71 ± 0.19, 8.48 ± 0.20 and 7.19 ± 0.21 kg respectively; where lambs born in Dry season'92 and Wet season'93 had significantly higher (P <0.001) weaning weight than those born in Dry season'93.

51

Table 12: Body weight (kg) of Menz and Horro lambs from birth to 180 days of age

Sources of

Variation

LS means(±SE) of body weight (kg) from birth to age(days):

n

birth

n

30

n

60

n

90

Overall

856

2.30

798

5.04

752

6.94

709

8.12

 

 

(±0.02)

 

(±0.06)

 

(±0.09)

 

(±0.12)

Breed

 

***

 

*

 

ns

 

ns

Menz

461

2.17

439

4.88

425

6.91

411

8.03

 

 

(±0.03)

 

(±0.08)

 

(±0.11)

 

(±0.12)

Horro

395

2.43

359

5.20

327

6.97

298

8.21

 

 

(±0.03)

 

(±0.08)

 

(±0.13)

 

(±0.13)

Sex

 

***

 

***

 

***

 

*

Female

427

2.22

390

4.88

366

6.75

344

7.96

 

 

(±0.02)

 

(±0.07)

 

(±0.11)

 

(±0.14)

Male

429

2.38

408

5.20

386

7.14

365

8.29

 

 

(±0.03)

 

(±0.07)

 

(±0.11)

 

(±0.14)

Birth Type

 

***

 

***

 

***

 

***

Single

668

2.59

633

5.86

608

8.13

577

9.46

 

 

(±0.02)

 

(±0.06)

 

(±0.09)

 

(±0.10)

Twins

188

2.01

165

4.21

144

5.75

132

6.79

 

 

(±0.03)

 

(±0.10)

 

(±0.16)

 

(±0.19)

Dam Parity

 

***

 

***

 

***

 

***

1

477

2.16

435

4.56

403

6.47

372

7.53

 

 

(±0.03)

 

(±0.08)

 

(±0.12)

 

(±0.15)

2

379

2.44

363

5.51

349

7.41

337

8.72

 

 

(±0.03)

 

(±0.07)

 

(±0.11)

 

(±0.13)

Birth Season

 

*

 

***

 

***

 

***

Dry'92

282

2.22b

272

4.77b

269

7.15b

254

8.71a

 

 

(±0.04)

 

(±0.11)

 

(±0.16)

 

(±0.19)

Wet'93

309

2.30a

289

5.51a

288

7.46a

288

8.48a

 

 

(±0.04)

 

(±0.11)

 

(±0.16)

 

(±0.20)

Dry'93

265

2.38a

237

4.83b

195

6.22c

167

7.19b

 

 

(±0.04)

 

(±0.11)

 

(±0.16)

 

(±0.21)

 

0.41

 

0.39

 

0.32

 

0.36

C.V. ( %)

 

17.1

 

21.0

 

21.5

 

21.0

ns = not significant; * = P < 0.05; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993


52

Post weaning growth

After weaning, the two breeds did not differ significantly (P >0.05) in weight up to 300 days of age (Tables 13). However, after 300 days of age Horro lambs tended to be heavier than Menz lambs as shown in Table 13. Effects of sex, birth type and birth season on weight were significant (p <0.001) even after weaning (Table 13). As shown in Figures 1 and 2, Horro and Menz lambs had a relatively similar growth curve.

Figure 3 shows that male lambs had maintained their weight superiority at birth throughout and the gap between body weights of male and female lambs tended to get wider after 120 days of age ( Tables 12 and 13). So were also single born lambs compared to twins.

Lambs born to second parity ewes were heavier throughout (P <0.001) compared to those born from first time lambers (Tables 12 and 13).

Season of birth has significantly (p <0.01) influenced lamb body weight at birth and at all stages of growth (Tables 12 and 13). Lambs born in the third season ( Dry'93) were lighter at all stages except at birth compared to the other groups (Tables 12 and 13).

Figure 1: Body weight of Menz and Horro lambs from birth to 180 days of age (LSM ± SE)

n at birth: 856 and at Age (days): 30: 798, 60: 752, 90 (weaning): 709, 120: 670, 150: 637, 180: 617, ns = not significant, * = P < 0.05, *** = P < 0.001


53

Figure 2: Body weight of male Menz and Horro lambs from birth to 365 days of age (LSM ± SE)

n at birth = 429 and at Age (days): 30 = 408, 60 = 386, 90 (weaning) = 365, 120 = 343, 150 = 325, 180 = 310, 210 = 292, 240 = 269, 270 = 258, 300 = 244, 330 = 234, 365 = 221, ns = not significant, * = P < 0.05, *** = P < 0.001

Figure 3: Body weight of Menz and Horro lambs from birth to 180 days of age by sex (LSM ± SE)

n at birth = 856 and at Age (days): 30 = 798, 60 = 752, 90 (weaning) = 709, 120 = 670, 150 = 637, 180 = 617, ns = not significant, * = P < 0.05, ** = P < 0.01, *** = P < 0.001


54

Table 13: Body weight (kg) of male Menz and Horro lambs from 120 to 365 days of age

Variation

LSMEANS(±SE) of Body Weight (kg) at Age(days):

n

120

n

180

n

240

n

300

n

365

Overall

343

9.09

310

11.53

269

14.28

244

16.15

221

19.41

 

 

(±0.22)

 

(±0.33)

 

(±0.41)

 

(±0.46)

 

(±0.55)

 

 

 

 

 

 

 

 

 

 

 

Breed

 

ns

 

ns

 

ns

 

Ns

 

*

Menz

207

9.14

201

11.45

180

14.24

162

16.21

149

19.12

 

 

(±0.25)

 

(±0.28)

 

(±0.35)

 

(±0.40)

 

(±0.47)

Horro

136

9.03

109

11.61

89

14.32

82

16.09

72

19.70

 

 

(±0.33)

 

(±0.38)

 

(±0.47)

 

(±0.51)

 

(±0.63)

 

 

 

 

 

 

 

 

 

 

 

Birth Type

 

***

 

***

 

***

 

***

 

***

Single

287

10.35

262

12.88

233

15.76

211

17.62

191

21.59

 

 

(±0.20)

 

(±0.21)

 

(±0.25)

 

(±0.28)

 

(±0.33)

Twins

56

7.82

48

10.18

36

12.80

33

14.68

30

18.42

 

 

(±0.35)

 

(±0.42)

 

(±0.55)

 

(±0.62)

 

(±0.75)

 

 

 

 

 

 

 

 

 

 

 

Dam Parity

 

***

 

***

 

**

 

*

 

**

1

178

8.53

161

10.96

138

13.66

125

15.71

117

19.28

 

 

(±0.28)

 

(±0.32)

 

(±0.41)

 

(±0.46)

 

(±0.55)

2

265

9.64

149

12.09

131

14.90

119

16.59

104

20.73

 

 

(±0.24)

 

(±0.28)

 

(±0.35)

 

(±0.39)

 

(±0.47)

 

 

 

 

 

 

 

 

 

 

 

Birth Season

 

***

 

*

 

***

 

***

 

***

Dry'92

122

9.45b

102

12.26a

99

17.90a

89

20.45a

78

25.16a

 

 

(±0.35)

 

(±0.40)

 

(±0.48)

 

(±0.53)

 

(±0.67)

Wet'93

147

10.04a

136

11.33b

99

12.50b

93

14.21b

89

17.93b

 

 

(±0.34)

 

(±0.39)

 

(±0.50)

 

(±0.56)

 

(±0.67)

Dry'93

74

7.77c

72

10.99b

71

12.45b

62

13.79b

54

16.93b

 

 

(±0.36)

 

(±0.42)

 

(±0.50)

 

(±0.57)

 

(±0.70)

 

0.32

 

0.32

 

0.64

 

0.65

 

0.66

C.V. ( %)

 

21.7

 

19.2

 

17.4

 

16.3

 

15.3

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993

Figure 4 shows growth curves for lambs born over the three lambing seasons. Lambs born in the Dry Season'92 and those born in the Wet Season'93 had relatively similar growth curves up to 150 days of age being significantly superior to that of lambs born in Dry Season'93 lambs. Dry Season'92 male lambs grew significantly (P <0.001) faster compared to male lambs from the other two groups (Wet Season'93 and Dry Season'93) which showed more or less a similar growth patern (Figure 4).


55

Figure 4: Body weight (LSM ± SE) of male Menz and Horro lambs from birth to 365 days of age by season of birth

n by birth = 429 and by Age (days): 30 = 408, 60 = 386, 90 (weaning) = 365, 120 = 343, 150 = 325, 180 = 310, 210 = 292, 240 = 269, 270 = 258, 300 = 244, 330 = 234, 365 = 221

4.1.2 Average daily weight gain (ADG)

Menz and Horro lambs did not differ significantly (p >0.05) in both preweaning and postweaning average daily gain (Tables 14 and 15). Horro lambs gained 89.25 ± 2.41 g compared to 89.22 ± 2.21 g for Menz lambs between birth and one month of age.

Table 14 shows that male lambs had a faster rate of weight gain compared to females between birth and 30 days of age (P <0.05) and between weaning (90 days of age) and 180 days of age (P <0.01). The difference in rate of weight gain between birth and weaning for the two groups was not significant (P >0.05). The rate of weight gains for male and female lambs of both breeds between the above age ranges are (91.79 ± 2.15 g vs 86.68 ± 2.07 g; 69.96 ± 1.55 g vs 67.62 ± 1.52 g; and 27.84 ± 1.19 g vs 24.62 ± 1.15 g, respectively).

Single born lambs had a significantly higher (P <0.001) average daily weight gain between birth and 30 days of age (109.06 ± 1.65 g) compared to twins (69.41 ± 2.87 g). As shown in Table 14, single born lambs have continued to grow faster (P <0.001) to weaning (90 days of age) compared to twins twins (81.34 ± 1.17 g for singles and 56.23 ± 2.14 g for twins, respectively).

Lambs born from ewes of second parity had a significantly faster (P <0.001) pre-weaning growth rate than those born from first time lambers (Tables 14 and 15).


56

Although the effect of season of birth on growth rate could not be conclusive due to the fact that the wet season lambing was not replicated, lambs born in the wet season had a slightly better pre-weaning growth rate compared to those born into the dry season (Tables 14 and 15) still indicating seasonal influence on growth performance. Lambs born at the first dry season lambing time (Dry'92), had performed well throughout compared to those born in the other two seasons.

57

Table 14: Average daily gain (ADG) of Menz and Horro lambs from birth to 180 days of age

Sources of Variation

LSMEANS(±SE) of ADG(g) Between Ages (Days)

Birth to 30

Birth to 90

90 to 180

ADG1

ADG2

ADG3

Overall

89.24±1.75

68.79±1.31

26.23±1.01

 

 

 

 

Breed

Ns

Ns

ns

Menz

89.22±2.21

69.43±1.58

26.24±1.12

Horro

89.25±2.41

68.14±1.83

26.21±1.47

 

 

 

 

Sex

*

ns

**

Female

86.68±2.07

67.62±1.52

24.62±1.15

Male

91.79±2.15

69.96±1.55

27.84±1.19

 

 

 

 

Birth Type

***

***

ns

Single

109.06±1.65

81.34±1.17

25.50±0.86

Twins

69.41±2.87

56.23±2.14

26.96±1.65

 

 

 

 

Dam Parity

***

***

ns

1

80.40±2.21

63.28±1.67

26.53±1.27

2

98.07±2.09

74.29±1.46

25.93±1.10

 

 

 

 

Birth Season

***

*

***

Dry'92

97.83a±3.01

74.21b ±2.17

25.91b±1.68

Wet'93

87.62b±3.11

78.45a±2.20

18.07c±1.60

Dry'93

82.26b±3.02

53.70c±2.30

34.70a±1.69

0.26

0.35

0.26

C.V. ( %)

32.7

26.8

57.4

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993


58

Table 15: Average daily gain (ADG) of male Menz and Horro lambs from birth to 365 days of age

Sources of Variation

LSMEANS(±SE) of ADG(g) Between Ages (Days)

Birth to 30

Birth to 90

90 to 180

180 to 270

270 to 365

Birth to 365

ADG1

ADG2

ADG3

ADG4

ADG5

ADG6

Overall

93.16±2.82

69.08±2.11

27.39±2.01

35.91±2.27

53.99±2.69

48.78±1.42

 

 

 

 

 

 

 

Breed

ns

Ns

ns

Ns

*

Ns

Menz

94.42±3.70

70.92±2.51

27.65±1.72

35.96±1.95

50.62±2.20

47.31±1.17

Horro

91.91±3.73

67.25±2.99

27.12±2.30

35.86±2.59

57.36±3.17

50.25±1.68

 

 

 

 

 

 

 

Birth Type

***

***

ns

ns

ns

**

Single

114.62±2.58

82.42±1.85

28.08±1.29

37.94±1.38

53.16±1.62

52.01±0.86

Twins

71.71±4.53

55.75±3.34

26.69±2.54

33.88±3.07

54.83±3.75

45.56±1.99

 

 

 

 

 

 

 

Dam Parity

***

***

ns

ns

ns

*

1

84.42±3.59

63.24±2.70

28.31±1.95

35.85±2.27

54.00±2.73

47.34±1.45

2

101.91±3.18

74.93±2.24

26.46±1.69

35.97±1.95

53.99±2.34

50.22±1.24

 

 

 

 

 

 

 

Birth Season

**

***

*

***

***

***

Dry'92

105.52a±4.53

74.93a±3.31

27.64b±2.42

71.87a±2.68

62.41a±3.33

62.02a±1.76

Wet'93

91.81b±4.61

78.30a±3.30

17.70c±2.33

17.52b±2.79

52.23b±3.31

43.55b±1.75

Dry'93

82.17b±4.58

54.02c±3.52

36.81a±2.55

18.34b±2.78

47.35b±3.53

40.78b±1.87

0.31

0.37

0.32

0.81

0.29

0.63

C.V. ( %)

33.0

27.5

54.0

36.2

31.4

16.8

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993

Though not significantly different (p >0.05), Menz lambs had a slightly better pre-weaning growth performance when weight gain between birth and weaning age (90 days) is considered (Tables 14 and 15). After 270 days of age, male Horro lambs seem to grow faster than male Menz lambs of the same age group (Table 15).

There was a sharp drop in rate of weight gain after weaning for all lambs (Figure 5) and for male lambs (Figure 6). This could partly be due to the weaning shock. The trend of recovery from the weaning shock for male lambs is shown in Figure 6.

As expected, the rate of growth before weaning (birth to 30 days of age) for all groups was relatively higher compared to that exhibited after weaning (Figures 5 and 6).


59

As shown in Table 15, the average daily body weight gain of male Menz and Horro lambs has increased after 180 days of age but at a reduced rate.

Figure 5: Average daily weight gain, ADG of Menz and Horro lambs between birth and 180 days of age (LSM ± SE)

ns = not significant

Figure 6: LSM ± SE of Average daily weight gain (ADG) of male Menz and Horro lambs between birth and 365 days of age

ns = not significant, * = P < 0.05


60

The relatively better performance of the Menz lambs at earlier age could be attributed to their adaptation to the environment of the experiment station, while the Horro sheep were brought from another region where environmental stresses particularly due to feed shortages and health challenges are not as high as those encountered in Debre Birhan area.

The magnitude of the difference in average daily weight gain of male Menz and Horro lambs at various stages of growth is shown by the deviation of the ADG Least Squares means of the two breeds from the overall mean (Figure 7 ).

Figure 7: Deviation in average daily body weight gain (ADG) of male Menz and Horro lambs between various stages of growth from birth (Constant = LS overall mean)

4.1.3 Lamb survival rate

Of the 856 lambs included in this analysis, 96.4 ± 0.01 % of Menz lambs and 93.5 ± 0.02 % Horro lambs survived to 15 days of age, the differences being not significantly different (P >0.05). As shown in Table 16, more (P <0.05) Menz lambs of those born have survived to the age of 30 days than the Horro (95.5 ± 0.02 % vs 91.2±0.02 %). Menz lambs had maintained their high survival rate at 90 180, 270 and 365 days of age. The survival rates observed were 89.4 ± 0.02, 81.3 ± 0.02, 71.5±0.02 and 62.4 ± 0.03 % for Menz lambs and 75.7 ± 0.03, 50.6 ± 0.03, 39.0 ± 0.03 and 37.3 ± 0.03 % for Horro lambs. The differences in survival rate at the respective age group between the two breeds are statistically significant (P <0.001). As shown in Figure 8, only some 50 % of Horro lambs born survived to 180 days of age and less than 40 % of the Horro lambs have survived to to the age of nine months.


61

Figure 8: Survival rate of Menz and Horro lambs to various stages of growth


62

Table 16: Survival rate of Menz and Horro lambs from birth to 365 days of age

Sources of Variation

Survival Rate ( %) from Birth to Age (days)

n (at birth)

15

30

90 (weaning)

180

270

365

Overall

856

95.2

93.7

83.7

67.8

55.8

49.5

 

 

(±0.01)

(±0.01)

(±0.02)

(±0.02)

(±0.02)

(±0.02)

 

 

 

 

 

 

 

 

Breed

 

Ns

*

***

***

***

***

Menz

461

96.4

95.5

89.4

81.3

71.5

62.4

 

 

(±0.01)

(±0.02)

(±0.02)

(±0.02)

(±0.02)

(±0.03)

Horro

395

93.5

91.2

75.7

50.6

39.0

37.3

 

 

(±0.02)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

(±0.03)

 

 

 

 

 

 

 

 

Sex

 

ns

Ns

ns

ns

***

***

Female

427

94.2

92.1

82.0

69.4

62.5

58.9

 

 

(±0.01)

(±0.01)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

Male

429

96.0

95.0

85.2

66.2

49.0

40.7

 

 

(±0.01)

(±0.01)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

 

 

 

 

 

 

 

 

Birth Type

 

***

***

***

***

***

***

Single

668

97.5

96.5

91.4

82.6

73.8

65.0

 

 

(±0.01)

(±0.01)

(±0.01)

(±0.02)

(±0.02)

(±0.02)

Twins

188

91.0

88.8

71.2

48.4

36.2

34.7

 

 

(±0.02)

(±0.02)

(±0.04)

(±0.04)

(±0.04)

(±0.04)

 

 

 

 

 

 

 

 

Parity

 

**

***

***

***

***

***

1

477

91.7

90.0

74.7

58.3

46.8

42.8

 

 

(±0.02)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

(±0.03)

2

379

97.3

96.1

89.9

76.1

64.5

56.8

 

 

(±0.01)

(±0.01)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

 

 

 

 

 

 

 

 

Birth Season

 

*

*

***

***

***

*

Dry'92

282

98.0a

96.9a

90.2a

67.4b

62.5a

53.3b

 

 

(±0.01)

(±0.01)

(±0.02)

(±0.03)

(±0.03)

(±0.03)

Wet'93

309

93.6b

91.9b

91.1a

83.6a

64.2a

61.3a

 

 

(±0.02)

(±0.02)

(±0.02)

(±0.02)

(±0.03)

(±0.03)

Dry'93

265

91.5b

90.0b

58.9b

47.1c

40.4b

35.1c

 

 

(±0.02)

(±0.02)

(±0.04)

(±0.04)

(±0.04)

(±0.03)

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993

Male and female lambs did not have significantly different (P >0.05) survival rates from birth to

15, 30, 90 and 180 days of age (Table 16). However, after 180 days of age, the survival rate of male lambs dropped drastically compared to that of the female (P <0.001). This is most probably due to the preferential treatment of the ewe lambs in preparation to mating.


63

As expected, single born lambs had a better survival rate (p <0.001) than twins to 15, 30, 90, 180, 270 and 365 days of age (97.5 ± 0.01, 96.5 ± 0.01, 91.4 ± 0.01, 82.6 ± 0.02, 73.8 ± 0.02 % and 65.0 ± 0.02 vs 91.0 ± 0.02, 88.8 ± 0.02, 71.2 ± 0.04, 48.4 ± 0.04, 36.2 ± 0.04 and 34.7 ± 0.04 %, respectively). Major reduction in survival rate occurred between weaning (90 days of age) and 180 days of age.

Lambs born from ewes of second parity had a higher survival rate to all ages compared to those born from ewes of first parity (Table 16). The high loss of lambs born to first time lambers (first parity ewes), during the pre-weaning growth phase, indicates the influences of lower birth weight and probably lower milk producing ability of first parity ewes.

Birth season had influenced survival rate of lambs to the various ages significantly. Lambs born at the beginning of the dry season of 1992/93 had a better survival rate (p <0.05) from birth to 15 and 30 days of age compared to those born in the other seasons (Table 16). However, lambs born at the beginning of the wet season of 1993 (Wet'93) had a better survival rate after weaning (90 days of age) compared to the other two groups and this is probably due to the provision of quality pasture during the wet period.

The extremely drastic reduction in survival rates of lambs born in the Dry'93 season between weaning and 180 days indicates an exposure to a major disease challenge or a shortage of feed as lambs born in this season were weaned in the dry season.

4.2 Linear body measurements and their relation to body weight changes

The measures for size and body conformation of male Menz and Horro sheep are compared in Tables 17, 18, and 19 at 180, 270 and 365 days of age respectively.

Horro sheep are different in their body measurements from Menz, significantly only at the age of 365 days. They are taller and longer but have a comparable heart girth (Tables 19). Wither height at 180, 270 and 365 days of age were 50.93 cm, 55.13 cm, 59.89 cm for male Menz lambs and 52.06 cm, 57.86 cm, 61.91 for male Horro lambs, respectively.

As shown in Tables 17, 18 and 19, Horro lambs had also significantly longer tails than Menz lambs at 180, 270 and 365 days of age. Menz lambs on the other hand had wider (P <0.05) tail at 180 and 270 days of age compared to that of the Horro.


64

As shown in tables 21, 23 and 25, the best regressor of weight observed after a stepwise regression analysis was heart girth. In both breeds body weight at 6, 9 and 12 months of age could be fairly accurately estimated from heart girth measurements (Tables 21, 23, and 25). A similar analysis was made on body weight and linear body measurements of male lambs from both breeds which were born in the first season (Dry'92) and which were intensively fed for about 120 days. The relationship of weight and the linear body measurements considered above was similar to that described for all male lambs studied. As shown in Table 26, Horro lambs had a longer body length, had a taller wither height and had a longer tail compared to Menz lambs of the same age group at all stages. However, after the first eight weeks of fattening, Menz lambs exhibited larger (p <0.01) tail width and tail circumference compared to the Horro indicating fat deposition characteristics. The two breeds did not differ significantly (p >0.05) in heart girth and in tail volume measurements taken at all stages.

65

Table 17: Linear body measurements of male Menz and Horro lambs at 180 days of age

Sources of

LSMEANS(±SE) of Measurements

 

Heart-

Wither-

Body-

Tail

Variation

girth

Height

length

Length

width

circumference

 

n

(cm)

(cm)

(cm)

(cm)

(cm)

(cm)

Breed

Ns

Ns

ns

**

**

**

Menz 201

50.94

50.93

50.37

17.13

8.41

9.61

 

(±0.58)

(±0.56)

(±0.65)

(±0.54)

(±0.24)

(±0.29)

Horro 109

50.80

52.06

50.60

27.87

6.94

8.28

 

(±0.77)

(±0.74)

(±0.86)

(±0.71)

(±0.32)

(±0.38)

 

 

 

 

 

 

 

Birth Type

**

**

*

ns

**

**

Single 262

52.72

53.20

51.66

23.02

8.50

9.56

 

(±0.41)

(±0.39)

(±0.45)

(±0.38)

(±0.17)

(±0.20)

Twins 48

49.02

49.79

49.32

21.97

6.85

8.33

 

(±0.93)

(±0.89)

(±1.03)

(±0.86)

(±0.38)

(±0.46)

 

 

 

 

 

 

 

Dam Parity

ns

Ns

ns

ns

ns

ns

1 161

50.56

51.24

50.16

22.24

7.46

8.92

 

(±0.62)

(±0.60)

(±0.69)

(±0.58)

(±0.26)

(±0.31)

2 149

51.18

51.75

50.82

22.75

7.89

8.97

 

(±0.64)

(±0.62)

(±0.72)

(±0.59)

(±0.26)

(±0.32)

 

 

 

 

 

 

 

Birth Season

**

*

*

*

*

ns

Dry'92 102

53.09a

52.88b

49.89b

22.79a

7.80a

9.79a

 

(±0.64)

(±0.61)

(±0.71)

(±0.59)

(±0.26)

(±0.32)

Wet'93 136

50.05b

52.03a

52.09a

23.91a

8.24a

8.33b

 

(±1.04)

(±1.00)

(±1.16)

(±0.96)

(±0.43)

(±0.52)

Dry'93 72

49.48b

49.57b

49.49b

20.80b

6.99b

8.72b

 

(±0.71)

(±0.69)

(±0.53)

(±0.66)

(±0.29)

(±0.36)

 

 

 

 

 

 

 

0.49

0.50

0.39

0.80

0.53

0.44

C.V. ( %)

6.2

6.0

7.2

14.6

16.0

16.4

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993


66

Table 18: Linear body measurements of male Menz and Horro lambs at 270 days of age

Sources of

LSMEANS(±SE) of Measurements

 

Heart-

Wither-

Body-

Tail

Variation

girth

Height

length

Length

width

circumference

 

n

(cm)

(cm)

(cm)

(cm)

(cm)

(cm)

Breed

ns

**

ns

**

*

**

Menz 174

57.57

55.13

54.36

20.62

10.81

13.11

 

(±0.49)

(±0.45)

(±0.64)

(±0.51)

(±0.27)

(±0.32)

Horro 84

56.39

57.86

55.01

32.53

9.95

11.16

 

(±0.63)

(±0.58)

(±0.83)

(±0.66)

(±0.35)

(±0.41)

 

 

 

 

 

 

 

Birth Type

**

**

ns

Ns

ns

**

Single 224

58.29

57.55

55.61

26.13

10.67

12.90

 

(±0.35)

(±0.32)

(±0.45)

(±0.36)

(±0.19)

(±0.22)

Twins 34

55.67

55.45

53.76

27.02

10.09

11.36

 

(±0.79)

(±0.73)

(±1.03)

(±0.82)

(±0.43)

(±0.51)

 

 

 

 

 

 

 

Dam Parity

ns

Ns

ns

Ns

ns

ns

1 132

56.79

56.23

54.81

26.66

10.21

12.02

 

(±0.57)

(±0.52)

(±0.74)

(±0.59)

(±0.31)

(±0.37)

2 126

57.17

56.76

54.56

26.49

10.54

12.25

 

(±0.50)

(±0.46)

(±0.65)

(±0.52)

(±0.27)

(±0.32)

 

 

 

 

 

 

 

Birth Season

**

**

**

**

*

*

Dry'92 96

62.32a

59.92a

58.57a

29.15a

12.71a

15.14a

 

(±0.66)

(±0.61)

(±0.87)

(±0.69)

(±0.36)

(±0.43)

Wet'93 96

54.86b

54.51b

53.20b

25.24b

8.61b

9.98c

 

(±0.71)

(±0.65)

(±0.92)

(±0.74)

(±0.39)

(±0.46)

Dry'93 66

53.76b

55.05b

52.28b

25.34b

9.82c

11.27b

 

(±0.68)

(±0.63)

(±0.89)

(±0.71)

(±0.37)

(±0.44)

 

 

 

 

 

 

 

0.65

0.64

0.46

0.80

0.64

0.63

C.V. ( %)

5.9

5.5

8.0

15.0

17.2

16.9

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993


67

Table 19: Linear body measurements of male Menz and Horro lambs at 365 days of age

Sources of

LSMEANS(±SE) of Measurements

 

Heart-

Wither-

Body-

Tail

Variation

girth

Height

length

Length

width

circumference

 

n

(cm)

(cm)

(cm)

(cm)

(cm)

(cm)

Breed

ns

***

*

***

ns

ns

Menz 149

61.53

59.89

58.12

22.52

12.55

14.96

 

(±0.50)

(±0.44)

(±0.67)

(±0.62)

(±0.32)

(±0.35)

Horro 72

61.11

61.91

60.38

36.28

11.82

14.37

 

(±0.70)

(±0.62)

(±0.94)

(±0.87)

(±0.45)

(±0.49)

 

 

 

 

 

 

 

Birth Type

*

Ns

ns

Ns

ns

ns

Single 191

62.44

61.40

59.77

28.72

12.65

15.15

 

(±0.36)

(±0.32)

(±0.49)

(±0.45)

(±0.24)

(±0.25)

Twins 30

60.19

60.40

58.73

30.08

11.72

14.18

 

(±0.86)

(±0.77)

(±1.17)

(±1.07)

(±0.56)

(±0.61)

 

 

 

 

 

 

 

Dam Parity

ns

Ns

ns

Ns

ns

Ns

1 117

61.09

61.13

59.57

29.34

12.23

14.64

 

(±0.61)

(±0.55)

(±0.83)

(±0.76)

(±0.40)

(±0.43)

2 104

61.54

60.67

58.93

29.46

12.15

14.69

 

(±0.35

(±0.47)

(±0.72)

(±0.66)

(±0.35)

(±0.38)

 

 

 

 

 

 

 

Birth Season

*

***

***

***

***

***

Dry'92 78

65.67a

64.42a

64.11a

31.91a

14.05a

16.38a

 

(±0.75)

(±0.67)

(±1.01)

(±0.93)

(±0.49)

(±0.53)

Wet'93 89

60.23b

59.72b

56.94b

28.52b

11.64b

14.34b

 

(±0.73)

(±0.65)

(±0.99)

(±0.91)

(±0.48)

(±0.51)

Dry'93 54

58.05c

58.56b

56.70b

27.76b

10.87b

13.28b

 

(±0.80)

(±0.71)

(±1.08)

(±0.99)

(±0.52)

(±0.56)

 

 

 

 

 

 

 

0.60

0.63

0.54

0.79

0.42

0.38

C.V. ( %)

5.4

4.9

7.7

15.9

17.0

15.4

ns = not significant; * = P < 0.05; ** = P < 0.01; *** = P < 0.001; Birth Season: Dry'92= born October/November 1992; Wet'93= born June/July 1993; Dry'93= born November/December 1993


68

Menz lambs had as expected a wider tail, hence, a larger tail circumference at 180, 270, and 365 days of age (Tables 17, 18 and 19). However, tail circumference measurements of Menz and Horro at 365 days of age (14.96 and 14.37 cm, respectively) were not significantly different (p >0.05).

The difference in heart girth between singles and twins was significant at 180 and 270 days of age (p <0.01) and at 365 days of age (p <0.05). This is more likely a reflection of the body condition status of the animals rather than the expression of birth type effect on heart girth.

The deviations of body weight and linear body measurements of Menz and Horro lambs from overall LS Means at 180 and 365 days of age are shown in Figures 9 and 10. These clearly reflect the differences explained above where Horro lambs had above average measurements except for tail width and tail circumference measurements. At all stages of growth, the two breeds differ greatly in tail length as the Horro sheep is characterised to have a long fat tail.

Figure 9: Deviation of linear body measurements (cm) from overall LS means for male Menz and Horro lambs at 180 days of age


69

Figure 10: Deviation of linear body measurements (cm) from overall LS means for male Menz and Horro lambs at 365 days of age

The positive correlation observed between body weight and linear body measurements is highly significant (p <0.01) for both breeds (Tables 20, 22 and 24). As expected, heart girth measurement is the best regressor of body weight at various ages compared to the other linear body measurements for both Menz and Horro lambs.

The regression R² shows that these correlations are slightly higher for Menz lambs than for the Horro (Tables 21, 23, and 25). At the age of 6 months, body weight in Menz lambs can be fairly accurately estimated from heart girth, wither height and tail circumference measurements (Table 21). At the same age, however, the best possible body weight estimate for Horro lambs could be calculated using heart girth, body length and tail circumference measurements (Table 21). At 9 months of age (Tables 23), a slightly higher R² was observed and a relatively better weight estimate could be achieved by using heart girth, wither height and tail width measurements for Menz ( R²=0.88) and including heart girth, body length and tail circumference for Horro (R²=0.82).

However, by including other linear body measurements such as wither height, body length, or some of the tail measurements depending on their significant contribution in the Stepwise regression analysis weight prediction could be substantially improved (Tables 21, 23 and 25).


70

Table 20: Correlation coefficients of body weight and linear body measurements for male Menz and Horro lambs at 6 months of age (n=129 and 67 respectively)

Menz (upper diagonal)/ Horro (lower diagonal)

Body weight

Heart girth

Wither height

Body length

Tail length

Tail width

Tail circumference

 

 

***

***

***

***

***

***

Body weight

-

0.88

0.83

0.71

0.39

0.70

0.78

Heart girth

0.86

-

0.83

0.70

0.39

0.69

0.77

Wither height

0.67

0.67

-

0.69

0.41

0.68

0.67

Body length

0.63

0.57

0.64

-

0.39

0.63

0.54

Tail length

0.59

0.51

0.72

0.51

-

0.25

0.30

Tail width

0.68

0.53

0.55

0.48

0.67

-

0.77

Tail circumference

0.63

0.56

0.57

0.35

0.54

0.75

-

** *P < 0.001

Table 21: Regression models for predicting body weight of Menz and Horro ram lambs from some linear body measurements (HG, WH, BL, TC, TW)* at 180 days of age

Models and independent variables

A

b1

b2

b3

 

 

 

 

 

 

Menz

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-14.9768

0.5204

--

 

0.77

a + b1HG + b2WH

-16.9601

0.3573

0.2024

--

0.80

a + b1HG + b2WH + b3TC

-14.6564

0.2709

0.1914

0.2722

0.82

 

 

 

 

 

 

Horro

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-17.8938

0.5803

--

 

0.67

a + b1HG + b2BL

-21.4145

0.4719

0.1806

--

0.72

a + b1HG + b2BL + b3TW

-19.7373

0.4204

0.1480

0.3695

0.74

*HG= Heart girth; WH= Wither height; BL= Body length; TW= Tail width; TC= Tail circumference


71

Table 22: Correlation coefficients of body weight and body linear measurements for male Menz and Horro lambs at 9 months of age (n=174 and 83 respectively)

Menz (upper diagonal)/ Horro (lower diagonal)

Body weight

Heart girth

Wither height

Body length

Tail length

Tail width

Tail circumference

 

 

***

***

***

***

***

***

Body weight

-

0.89

0.86

0.80

0.49

0.82

0.85

Heart girth

0.84

-

0.87

0.76

0.49

0.78

0.84

Wither height

0.68

0.78

-

0.77

0.52

0.78

0.79

Body length

0.73

0.77

0.73

-

0.48

0.73

0.69

Tail length

0.66

0.75

0.68

0.74

-

0.58

0.56

Tail width

0.69

0.74

0.65

0.68

0.69

-

0.92

Tail circumference

0.74

0.81

0.65

0.67

0.73

0.87

-

** *P < 0.001

Table 23: Regression models for predicting body weight of Menz and Horro ram lambs from some linear body measurements (HG, WH, BL, TW, TC)* at 270 days of age

Models and independent variables

A

b1

b2

B3

 

 

 

 

 

 

Menz

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-25.1949

0.7145

--

 

0.83

a + b1HG + b2TW

-18.1381

0.4903

0.5377

--

0.88

a + b1HG + b2WH + b3TW

-21.3931

0.3931

0.1735

0.4650

0.88

 

 

 

 

 

 

Horro

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-28.7136

0.7778

--

 

0.82

a + b1HG + b2TC

-19.8443

0.5354

0.4257

--

0.87

a + b1HG + b2BL + b3TC

-20.8628

0.4449

0.1178

0.3992

0.88

*HG= Heart girth; WH= Wither height; BL= Body length; TW= Tail width; TC= Tail circumference


72

Table 24: Correlation coefficients of body weight and body linear measurements for male Menz and Horro lambs at 12 months of age (n=150 and 71 respectively)

Menz (upper diagonal)/ Horro (lower diagonal)

Body weight

Heart girth

Wither height

Body length

Tail length

Tail width

Tail circumference

 

 

***

***

***

***

***

***

Body weight

-

0.90

0.80

0.76

0.41

0.74

0.72

Heart girth

0.86

-

0.80

0.72

0.41

0.73

0.73

Wither height

0.78

0.79

-

0.74

0.43

0.62

0.60

Body length

0.77

0.77

0.75

-

0.47

0.56

0.52

Tail length

0.75

0.75

0.70

0.73

-

0.44

0.40

Tail width

0.76

0.74

0.72

0.71

0.75

-

0.89

Tail circumference

0.73

0.74

0.66

0.65

0.76

0.89

-

** *P < 0.001

Table 25: Regression models for predicting body weight of Menz and Horro ram lambs from some linear body measurements (HG, WH, BL, TL, TW, TC)* at 365 days of age

Models and independent variables

A

b1

b2

b3

 

 

 

 

 

 

Menz

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-35.0606

0.8938

--

 

0.83

a + b1HG + b2BL

-36.2150

0.7209

0.2044

--

0.85

a + b1HG + b2BL + b3TW

-31.4011

0.5734

0.1922

0.3919

0.88

 

 

 

 

 

 

Horro

 

 

 

 

 

 

 

 

 

 

 

a + b1HG

-40.3616

0.9947

--

 

0.81

a + b1HG + b2WH

-50.4522

0.7469

0.4061

--

0.84

a + b1HG + b2WH + b3BL

-47.7159

0.6620

0.3159

0.1352

0.85

*HG= Heart girth; WH= Wither height; BL= Body length; TW= Tail width


73

Linear body measurements were also taken from male Menz and Horro lambs born during the first lambing season and which were in the fattening study (Table 26). All measurements were taken fortnightly. Menz lambs seem to have larger heart girth measurement than the Horro, though not significantly different (p >0.05). Wither height, body length and tail length have the same trend as that for all the groups and were significantly higher (p <0.01) for Horro compared to that of the Menz lambs (Table 26). Menz lambs had differed significantly (p <0.01) from Horro in tail width and tail circumference. The two breeds did not differ significantly (P >0.05) in tail volume measured by water displacement method.

74

Table 26: Weight and body linear measurements of Male Menz and Horro lambs during the fattening period

 

LSMEANS (±SE) of Parameters Measured

 

Body

Heart-

Wither

Body

Tail

 

Wt.

Girth

Height

Length

Length

Width

Circumf.

Volume

 

kg

cm

cm

Cm

cm

cm

cm

ml

Week 1

 

 

 

 

 

 

 

 

 

ns

Ns

**

**

**

ns

ns

ns

Menz

26.4

71.6

61.6

61.6

23.2

15.2

16.4

730.3

 

(±0.52)

(±0.58)

(±0.72)

(±0.43)

(±0.52)

(±0.33)

(±0.28)

(±34.77)

Horro

27.3

71.2

64.7

64.9

40.1

14.3

15.7

774.1

 

(±0.68)

(±0.67)

(±0.83)

(±0.50)

(±0.60)

(±0.38)

(±0.33)

(±40.42)

 

 

 

 

 

 

 

 

 

0.44

0.39

0.38

0.61

0.92

0.33

0.42

0.25

C.V.( %)

11.1

4.6

6.5

3.9

9.6

12.7

10.0

26.4

Week 8

 

 

 

 

 

 

 

 

 

ns

ns

**

**

**

**

**

ns

Menz

29.8

74.9

63.2

61.8

27.7

19.9

22.9

1369.5

 

(±0.53)

(±0.55)

(±0.52)

(±0.67)

(±0.63)

(±0.32)

(±0.35)

(±49.39)

Horro

31.2

73.8

66.4

67.0

42.4

16.8

21.2

1357.8

 

(±0.64)

(±0.64)

(±0.61)

(±0.78)

(±0.73)

(±0.37)

(±0.35)

(±57.42)

 

 

 

 

 

 

 

 

 

0.46

0.33

0.50

0.56

0.86

0.57

0.35

0.20

C.V.( %)

9.8

4.2

4.6

6.0

10.4

9.7

9.0

20.6

Week 16

 

 

 

 

 

 

 

 

 

*

ns

**

**

**

**

**

ns

Menz

32.7

71.9

68.1

68.8

29.9

20.7

25.3

1895.3

 

(±0.61)

(±0.46)

(±0.53)

(±0.36)

(±0.62)

(±0.32)

(±0.37)

(±55.35)

Horro

34.7

71.7

69.9

70.8

44.3

18.0

23.6

1881.0

 

(±0.70)

(±0.51)

(±0.59)

(±1.40)

(±0.69)

(±0.35)

(±0.41)

(±61.13)

0.47

0.43

0.40

0.54

0.88

0.51

0.31

0.39

C.V.( %)

9.7

3.5

4.2

2.8

9.2

8.9

8.3

16.0

ns = not significant * = P < 0.05 ** = P < 0.01 Tail circumf. = Tail circumference


75

4.3 Fattening performance of male lambs

4.3.1 Weight gain and feed intake of male Menz and Horro lambs

At one year of age, all available male lambs (34 Menz and 26 Horro) born in the first lambing season of the programme were included in a fattening performance study. The study was undertaken for 123 days excluding two weeks of adaptation period.

Least Squares means and standard errors of initial body weight, unfasted final body weight, fasted final body weight (slaughter weight), age at slaughter, hot and cold carcass weight and dressing percentage are presented in Table 27.

There was no significant difference (p >0.05) in body weight at the beginning of the experiment (Table 27). The mean initial body weights were 26.4 ± 0.52 kg and 27.3 ± 0.68 kg for Menz and Horro lambs respectively. However, at the end of the fattening study Horro lambs attained significantly heavier (p <0.05) final weight compared to Menz lambs (34.7 ± 0.63 kg for Horro and 32.7 ± 0.57 kg Menz). This weight difference was also reflected in the slaughter weight which was taken after fasting the animals for 16 hours and prior to slaughter.

Despite the clear tendency of Horro lambs having a heavier hot and cold carcass weight, Horro lambs did not differ significantly (P >0.05) from the Menz in dressing % and loss of carcass moisture (shrinking %) after an overnight cold room storage (Table 27). The slightly higher but not significantly different (P >0.05) loss of moisture from Horro lamb carcasses compared to carcasses from Menz lambs indicates that carcasses from Menz lambs had a better fat cover.


76

Table 27: Fattening and carcass performance of Male Menz and Horro lambs

Parameters measured

LSMEANS(±SE) of parameters measured

 

 

Menz

Horro

Level of

 

 

(n=34)1

(n=26)

significance

C.V. ( %)

 

 

 

 

 

 

Initial body weight, kg

26.5

28.3

ns

0.36

12.5

 

(±0.63)

(±0.70)

 

 

 

 

 

 

 

 

 

Final body weight, kg

32.1

34.1

*

0.49

9.0

 

(±0.54)

(±0.61)

 

 

 

 

 

 

 

 

 

Average daily gain, g

45.5

47.3

ns

0.47

34.3

 

(±2.90)

(±3.81)

 

 

 

 

 

 

 

 

 

Slaughter weight (FBW)2, kg

28.9

31.0

*

0.44

10.3

 

(±0.56)

(±0.63)

 

 

 

 

 

 

 

 

 

Empty body weight, kg

23.1

24.0

**

0.36

10.8

 

(±0.46)

(±0.52)

 

 

 

 

 

 

 

 

 

Hot-carcass weight, kg

14.2

14.8

ns

0.42

9.9

 

(±0.26)

(±0.29)

 

 

 

 

 

 

 

 

 

Cold-carcass weight, kg

13.6

14.2

ns

0.41

10.3

 

(±0.26)

(±0.29)

 

 

 

 

 

 

 

 

 

Dressing %

49.1

48.0

ns

0.27

6.4

 

(±0.57)

(±0.64)

 

 

 

 

 

 

 

 

 

Shrinking %

3.8

4.2

ns

0.27

23.6

 

(±0.17)

(±0.19)

 

 

 

 

 

 

 

 

 

Age at slaughter, days

527.5

528.2

ns

0.41

1.5

 

(±1.42)

(±1.60)

 

 

 

ns = not significant; * = P < 0.05; ** = P < 0.01; 1 There were only 30 Menz lambs at slaughter time; 2 FBW= Fasted Body Weight


77

Menz and Horro lambs have also differed significantly in fresh weights and proportion to carcass of internal organs (GIT) as shown in Table 28. The fresh contents of the GIT were also weighed along with the corresponding GIT part. Horro lambs seem to have a significantly larger (p <0.01) gastro-intestinal-tract compared to Menz (Table 28). The fresh GIT content in proportion to slaughter weight for Horro lambs was 15.2 ± 0.52 % compared to 13.3 ± 0.46 % for the Menz, the difference being significant (P <0.05). This is also reflected in the amount of the dry matter intake by the two breeds where Horro lambs seem to have ingested more feed on dry matter basis than the Menz (Table 29). When the amount of dry matter intake is calculated on the basis of metabolic body weight, the intake of Horro was slightly higher (65.6 ± 1.72 per kg W0.75 for Menz and 67.8 ± 1.95 per kg W0.75 for Horro) but the difference was not significant. The faecal dry matter output was also higher (p <0.01) in Horro than in Menz lambs ( 426.2 g vs 366.0 g respectively) indicating a lower (p <0.01) digestibility estimate (51.6 % vs 54.0 %, respectively) as shown in Table 29.

78

Table 28: Fresh weight of different parts of the gastro-intestinal tract (GIT) from male Menz and Horro lambs

Gastro-Intestinal-Tract (GIT)

LSMEANS (±SE)

Level of

C.V.

Parts

Menz

Horro

significance

 

( %)

 

 

 

 

 

 

Hindgut (empty), g

1111.8

1273.0

**

0.44

15.7

 

(±34.18)

(±38.27)

 

 

 

 

 

 

 

 

 

Hindgut content, g

560.0

842.5

**

0.45

38.3

 

(±48.52)

(±54.33)

 

 

 

 

 

 

 

 

 

Forgut (empty), g

856.4

967.5

**

0.66

9.3

 

(±15.41)

(±17.25)

 

 

 

 

 

 

 

 

 

Forgut content, g

3287.6

3919.6

**

0.43

21.6

 

(±141.44)

(±158.37)

 

 

 

 

 

 

 

 

 

Reticulo-rumen (empty), g

661.9

745.2

**

0.60

10.3

 

(±13.25)

(±14.84)

 

 

 

 

 

 

 

 

 

Reticulo-rumen content, g

3097.8

3659.1

**

0.44

22.0

 

(±135.23)

(±151.42)

 

 

 

 

 

 

 

 

 

Omasum-Abomasum (empty), g

194.5

222.3

**

0.61

12.8

 

(±4.89)

(±5.47)

 

 

 

 

 

 

 

 

 

Omasum-Abomasum content, g

189.7

260.5

**

0.43

31.0

 

(±12.64)

(±14.16)

 

 

 

 

 

 

 

 

 

GIT Content as % of slaughter weight, kg

13.3

15.2

*

0.41

17.1

 

(±0.46)

(±0.52)

 

 

 

 

 

 

 

 

 

GIT with content as % of slaughter weight, kg

20.1

22.6

***

0.45

11.6

 

(±0.47)

(±0.53)

 

 

 

GIT = Gastrointestinal Tract; * = P < 0.05; ** = P < 0.01; *** = P < 0.001;


79

Table 29: Feed intake and digestibility estimate of male Menz and Horro lambs during fattening period

Variables

LSMEANS (±SE)

Level of

C.V.

Menz

Horro

Significance

 

( %)

 

 

 

 

 

 

Hay dry matter intake, g

435.1

506.0

**

0.62

11.1

 

(±9.28)

(±12.18)

 

 

 

 

 

 

 

 

 

Concentrate dry matter intake, g

367.1

373.6

**

0.40

2.1

 

(±1.42)

(±1.87)

 

 

 

 

 

 

 

 

 

Total dry matter intake, g

802.2

879.6

**

0.63

6.2

 

(±9.35)

(±12.27)

 

 

 

 

 

 

 

 

 

Dry matter intake, g/ kg W0.75

65.6

67.8

ns

0.48

14.3

 

(±1.72)

(±1.95)

 

 

 

 

 

 

 

 

 

Faecal dry matter, g

366.0

426.2

**

0.66

9.4

 

(±6.62)

(±8.68)

 

 

 

 

 

 

 

 

 

Digestibility estimate ( %)

54.0

51.6

**

0.53

5.4

 

(±0.01)

(±0.01)

 

 

 

 

 

 

 

 

 

** = P < 0.01

4.3.2 Carcass performance and body fat estimate of Male Horro and Menz lambs

4.3.2.1 Relative weights of carcasses and non-carcass components and dressing percentage

Although Horro lambs were heavier (P <0.05) at slaughter than the Menz, they had lower but not significantly different (P >0.05) dressing percent. The smaller and relatively compact Menz lambs on the other hand seem to have a slightly better dressing percentage. As indicated by Ruvuna et al. (1992), dressing percent is an important tool for evaluating carcass merit. However, since dressing percent is influenced by many factors such as breed, age, castration, feeding regime and fattening level (Ruvuna et al. 1992), care should be taken in interpreting results. Dressing percentages of Menz and Horro lambs (49.1 ± 0.57 % and 48.0 ± 0.64 %, respectively) observed in this study (Table 27) is in line with that reported by Enyew Negussie (1999) for one year old Menz and Horro lambs which is 48.7 ± 0.7 % for both breeds.


80

Soon after slaughter, hot (fresh) weight of carcasses and non-carcass parts were taken (Tables 27 and 28). Information on dissectible carcass composition for breeds was obtained by dissecting the left half of the carcasses after an overnight storage at 4oC. Proportion of the various components of whole carcasses were then estimated and analysed. Least Squares means and standard errors of dissected carcass parts and proportion of dissectible carcass components are presented in Table 30 and Figure 11.

There was no significant difference observed between the two breeds in dissectible carcass parts except total bone weight. Horro lambs had heavier (P <0.01) total carcass bone weight compared to Menz lambs (3.31 ± 0.08 kg vs 2.99 ± 0.07 kg). This could be attributed to the comparative larger body frame of the Horro compared to Menz sheep. However, there was no significant difference (P >0.05) in bone proportion when only the composition of the dissected part is considered (Figure 11) indicating that the two breeds have similar proportion of carcass components.

Table 30: Least Squares Means (± SE) of estimated whole carcass components and proportion of whole carcass parts from male Menz and Horro lambs

Carcass parts

LSMEANS(±SE)

C.V. ( %)

Proportion of whole carcass parts ( %)

Menz

Horro

Significance level

 

Menz

Horro

 

 

 

 

 

 

 

 

Total lean (dissectible), kg

8.55 (±0.19)

8.91 (±0.22)

ns

0.37

12.2

58.00

57.89

 

 

 

 

 

 

 

 

Total fat (dissectible), kg

2.88 (±0.11)

2.77 (±0.12)

ns

0.36

19.5

19.50

18.04

 

 

 

 

 

 

 

 

Total bone, kg

2.99 (±0.07)

3.31 (±0.08)

**

0.46

11.9

20.44

21.52

 

 

 

 

 

 

 

 

Total sundry, kg

0.30 (±0.04)

0.39 (±0.04)

ns

0.41

57.8

2.06

2.55

 

 

 

 

 

 

 

 

Total a

14.72

15.38

 

 

 

100

100

ns = not significant; * = P < 0.05; ** = P < 0.01; a The sum total of the carcass parts is higher than the actual carcass weight due to conversion and rounding up of figures


81

Figure 11: Carcass composition of the dissected left half carcasses of Menz and Horro lambs

Table 31: Least Squares Means and SE of carcass composition of the dissected left half carcasses from male Menz and Horro lambs

Breed

n

Carcass Composition ( %)

Lean (muscle)

Dissectible fat1

bone

sundry

Menz

31

62.34±0.52

14.17±0.62

21.46±0.42

2.11±0.27

 

 

 

 

 

 

Horro

26

62.41±0.59

13.00±0.70

22.32±0.47

2.27±0.30

Significance

 

Ns

Ns

ns

ns

 

 

 

 

 

 

 

0.25

0.31

0.30

0.39

 

 

 

 

 

 

C.V. ( %)

 

4.6

25.1

10.3

59.7

ns = not significantly different ; 1does not include tail fat


82

Table 32: Lean /bone and lean/fat ratio of whole and dissected half carcasses

Breed

Estimate for whole carcass

dissected half carcass

lean : bone

lean : fat

lean : bone

lean : fat

Menz

2.9±0.06

3.1±0.14

2.8±0.06

3.0±0.13

 

 

 

 

 

Horro

2.7±0.07

3.3±0.15

2.6±0.06

3.2±0.15

 

 

 

 

 

Significance

*

Ns

*

Ns

0.31

0.33

0.35

0.34

 

 

 

 

 

C. V. ( %)

11.5

22.3

11.3

22.5

ns = not significantly different; * = P <0.05

4.3.2.2 Direct and indirect estimation of total body fat

Based on the amount of dissectible body fat from the half carcasses, total dissectible body fat was estimated for both breeds (Tables 33). Least Squares means of body fat estimate in various carcass and non-carcass parts and proportion of the fat distribution (Figure 12 and Figure 13) show that both breeds have fairly similar body fat distribution.

However carcasses from Menz lambs had higher (P <0.05) total Ether extract estimate compared to that of the Horro (Table 33).

Menz lambs had a significantly higher (P <0.05) total ether extract estimate (Table 33) than the Horro. Dissectible fat in various carcass parts and other fat depots all indicate higher values for Menz sheep, though except for a significant difference (P <0.05) in estimated total lean ether extract (Table 33), all other differences fail the 95 % confidence level. Menz and Horro lambs compare well in terms of fat distribution as estimated by the ether extract with 32.1 % and 31.5 % subcutaneous fat, 29.0 % and 30.8 % tail/rump fat, 16.5 % and 15.1 % lean fat, 11.4 % and 11.2 % GIT fat, 4.6 % and 3.9 % gut fat, respectively.


83

Table 33: Least Squares Means ± SE of Ether extract estimate (g) of whole carcasses and non-carcass body components of Menz and Horro lambs

Carcass and non-carcass

LSMEAN(±SE)

 

 

 

component

Menz

Horro

Significance

C.V.(%)

Subcutaneous fat + IMF1

983.15±57.79

857.05±64.71

Ns

0.36

34.8

 

(32.1)2

(31.5)

 

 

 

 

 

 

 

 

 

Tail +Rump fat

885.37±30.14

838.37±33.75

Ns

0.40

19.3

 

(29.0)

(30.8)

 

 

 

 

 

 

 

 

 

Lean fat

505.18±25.86

411.00±28.95

*

0.38

30.7

 

(16.5)

(15.1)

 

 

 

 

 

 

 

 

 

GIT3 fat

347.79±20.81

303.60±23.30

Ns

0.47

35.0

 

(11.4)

(11.2)

 

 

 

 

 

 

 

 

 

Gut fat

140.95±12.04

105.30±13.48

ns

0.68

53.6

 

(4.6)

(3.9)

 

 

 

 

 

 

 

 

 

Sundry Fat

92.06±13.73

114.73±15.37

ns

0.44

74.6

 

(3.0)

(4.2)

 

 

 

 

 

 

 

 

 

Renal fat

59.23±4.72

45.10±5.28

ns

0.50

49.0

 

(1.9)

(1.7)

 

 

 

 

 

 

 

 

 

Urogenital fat

45.97±4.98

43.55±5.57

ns

0.34

62.9

 

(1.5)

(1.6)

 

 

 

Total Ether extract

3059.70±95.20

2718.7±106.60

*

0.52

18.1

 

(100.0)

(100.0)

 

 

 

 

 

 

 

 

 

Lean Ether extract (%)

22.4 ± 0.89

18.1 ± 1.00

**

0.43

23.9

ns = not significant; * = P < 0.05; ** = P < 0.01; 1 IMF denotes Inter-Muscular Fat; 2 Figures in parenthesis show percent of total Ether extract estimate; 3 GIT is gastro-intestinal tract


84

Although the difference in the estimated total dissectible fat for the two breeds was not significant (p >0.05), the estimated total ether extract for carcasses of Menz lambs was higher (p <0.05) than that for Horro ( Table 33). As shown in Table 33, the proportion of fat in the various carcass and non-carcass parts of both breeds were not significantly different (p >0.05). However as shown in Table 33, lean from Menz lambs had significantly higher (P <0.01) ether extract estimate on dry matter basis compared to that from Horro lambs (22.4±0.89 % and 18.1±1.00 %, respectively).

The higher lean ether extract estimate indicates that carcasses from Menz lambs have more inter- and intramuscular fat compared to that of the Horro. The correlations between tail volume measurements, tail weight, estimates of total fat in some carcass components and ether extract estimates are shown in Table 34. Total tail and rump fat estimates in Horro lambs had high correlation with tail volume measurements (ml) taken before slaughter (Tail V., l) and skinned tail volume measurement (Tail V., s) taken after slaughter. However in both breeds the correlation coefficients ( r = 0.66 and 0.79 for Menz and r = 0.78 and 0.92 for Horro ) between total tail/ rump fat and live tail volume and skinned tail volume, respectively were highly significant (P <0.001).

There is fairly similar strong and positive relationship (P <0.001) between subcutaneous fat and total dissectible fat and total ether extract estimate (r = 0.92 and 0.74 for Menz and r = 0.92 and 0.72 for Horro lambs, respectively). Tail and rump fat could be fairly accurately predicted in both breeds from tail volume measurements (Table 35). Nevertheless, as the regression equations in Table 35 indicate, tail volume measurements of Horro lambs could be used to estimate tail/rump weight as there is a very high correlation between the parameters compared to that of the Menz. On the other hand total body fat of Menz lambs could be predicted from tail /rump fat weight while total body fat in the Horro could be better predicted from tail volume (Table 36). As shown in Table 34, the relationship between total body fat, tail/rump fat weight and tail volume measurements does not seem to be strong. Therefore, it will be necessary to further investigate the usefulness of tail volume measurements for predicting body fat.


85

Table 34: Correlation of tail volume measurements, body fat depots and total body fat and Ether extract estimates

Menz/ (upper dgl.) Horro (lower dgl.)

Tail V. (l)

Tail V. (s)

TAILRU FAT

TOSFA

TOTFA

TOEE

Tail V. (l)

-

0.82 ***

0.66 ***

0.21 ns

0.40 *

0.17 ns

Tail V. (s)

0.65 ***

-

0.79 ***

0.26 ns

0.49 **

0.31 ns

TAILRU fat

0.78 ***

0.92 ***

-

0.19 ns

0.51 **

0.39 **

TOSFA

0.28 ns

0.08 ns

0.11 ns

-

0.91 ***

0.74 ***

TOTFA

0.50 **

0.32 ns

0.37 ns

0.94 ***

-

0.87 ***

TOEE

0.31 ns

0.15 ns

0.15 ns

0.72 ***

0.80 ***

-

ns = not significantly different; * = P <0.05; ** = P <0.01; *** = P <0.001; Tail V. (l) = Tail volume measured on live animal; Tail V. (s) = Skinned tail volume measured after slaughter; TAILRU fat = Total tail and rump fat wt; TOSFA = Total subcutaneous fat; TOTFA = The sum total of dissectible fat from the various carcass parts; TOEE = Total Ether extract (sum of ether extract estimates for the various carcass parts)


86

Figure 12: Carcass and non-carcass fat distribution of male Menz lambs

Figure 13: Carcass and non-carcass fat distribution of male Horro lambs

Table 35: Regression equations relating tail and rump fat weight (g) to tail volume measured on live animal (ml) and skinned tail volume (ml) taken after slaughter

Models and independent variables

a

b1

b2

Sig. Level

 

 

 

 

 

 

Menz

 

 

 

 

 

 

 

 

 

 

 

a + b1 TAIL VOLUME (skinned)

293.9418

0.6951

 

***

0.62

 

 

 

 

 

 

Horro

 

 

 

 

 

 

 

 

 

 

 

a + b1 TAIL VOLUME (skinned)

165.3888

0.7956

 

***

0.84

a + b1 TAIL V. (live) + b1 TAIL V. (skinned)

-106.6380

0.2504

0.6128

***

0.90

*** = P <0.001

Table 36: Regression equations relating estimated total disectable body fat (g) to tail volume measured on live animal (ml) and tail/rump fat weight (g) and skinned tail volume (ml) taken after slaughter

Models and independent variables

a

b1

Sig. level

 

 

 

 

 

Menz

 

 

 

 

 

 

 

 

 

a + b1 (TAILRU FAT)

1450.9485

1.4691

**

0.26

 

 

 

 

 

Horro

 

 

 

 

 

 

 

 

 

a + b1 TAIL VOLUME (live)

781.0795

1.1158

**

0.25

TAILRU FAT = TAIL/RUMP Fat weight; ** = P <0.01


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4.4 Discussion

4.4.1 Birth weight

Birth weight is one of the most important factors influencing particularly the pre-weaning growth rate of animals. Factors which influence birth weight include dam size, dam body condition (Laes-Fettback and Peters, 1995), management system, sex, litter size etc.(Notter et al. 1991), these should be properly addressed as both the pre-weaning survival and growth performance are greatly influenced by birth weight.

Birth weight of Horro lambs (2.43 ± 0.03 kg) and that of Menz lambs (2.17 ± 0.03 kg) observed in this study differ significantly (P <0.001). However, birth weight of Menz lambs reported here is lower than that reported for on-farm conditions by Niftalem Dibissa (1990). Both Horro and Menz lambs have birth weights comparable to birth weights of other tropical and sub-tropical breeds such as Adal (Galal, 1983), Djallonke (Filius et al. 1985 and Wunderlich, 1990), African fat tail sheep of Rwanda (Wilson and Murayi, 1988). Although Horro and Menz lambs have much lower birth weights when compared to larger tropical breeds like the Dorper or Mossi or large temperate breeds like Merinolandschaf, Finn sheep crosses etc., the birth weights of both breeds observed in this study are within the ranges reported from other studies (Table 4).

The condition of the ewe during the gestation period, breed size, sex, litter size, and age of dam are known to influence birth weight. It is also well documented that flock management practices undertaken, particularly management of the breeding ewes, greatly influence birth weight of lambs. Even when the same breed is studied under farm and station conditions, birth weight of the offspring from the two groups could most probably be different. Under optimal level of management, lambs born on station could have higher birth weights. However, under the given station condition with a heavy parasite burden and health problems resulting from overcrowding, lambs born under farm condition could have a higher birth weight compared to those born on station.

As expected, it is also observed in this study that male lambs had significantly higher (P <0.001) birth weights compared to females (2.38 ± 0.03 kg for males and 2.22 ± 0.02 kg for females. This is also in line with other research findings where males are mostly heavier than females.

Lambs born from ewes of second parity were heavier (P <0.001) than those born from ewes of first parity (2.44 ± 0.03 kg and 2.16 ± 0.03 kg respectively). This is a reflection of the influence of dam weight and size as ewes of second or higher parities are expected to be heavier than first parity ewes.


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In this study, mating of ewes was planned in such a way that lambing occurred either at the end of the main rainy season (October/November) or at the beginning of the main rainy season (June/July). As shown in Table 12, lambs born at the three lambing periods (Dry'92, Wet'93 and Dry'93,) had significantly different (P <0.05) birth weights (2.22 ± 0.04 kg, 2.30 ± 0.04 kg and 2.38 ± 0.04 kg, respectively). Although lambs born at the beginning of the main rainy season of Dry'93 tended to be heavier at birth (Table 12), this could not be conclusive as the Wet season lambing was not replicated. However this could probably be true due to the fact that ewes had a better quality pasture during the last two to three months of their gestation period than those which have lambed at the beginning of the 1993 wet season (Wet'93). Season of birth has also influenced birth weight significantly (P <0.05).

Despite the expectation that lambs born at the end of the rainy season to be heavier than those born at the beginning of the dry season mainly due to a better provision of pasture for the pregnant ewes towards the end of their gestation period, this is true only to lambs that were born in the Dry Season lambing of 1993 which were significantly heavier at birth compared to those born in the previous two seasons. Although this is likely to be the influence of qualitatively as well as quantitatively better forage availability of the ewes at the latter part of the gestation period, the result could not be conclusive as the wet season lambing was not replicated. However, the results indicate birth weight differences between the three lambing seasons.

4.4.2 Weaning weight, growth and average daily live weight gain (ADG)

As stated by Bathaei and Leroy (1996) and Orr (1982), growth could also be defined as an increase in body size and mass of the whole or part of the animal.

Although Horro and lambs seem to have similar growth performance as shown in Figures 1 and 2, they have differed in certain aspects. Apart from birth weight, Menz and Horro lambs have also differed in body weight, where Horro lambs maintained their superiority in birth weight during the pre-weaning growth phase. However, they were significantly (P <0.001) different only at one month of age (5.23 ± 0.07 kg for Horro and 4.74 ± 0.06 kg for the Menz).


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The body weights for Menz and Horro lambs at 60, 90 (weaning) and at 120 days of age were 6.91 ± 0.11, 8.03 ± 0.12 and 9.14 ± 0.25 kg for Menz and 6.97 ± 0.13, 8.21 ± 0.13 and 9.03 ± 0.33 kg for Horro, respectively. Horro lambs had also higher, though not significantly different (P >0.05), average pre-weaning daily weight gain compared to Menz. Mean ADG between birth and 30 of age were 90.61 ± 1.87 g for Horro and 86.06 ± 1.76 g for Menz lambs (Table 14). However, when the average daily weight gain of lambs from birth to weaning (90 days) is considered, Menz lambs seem to have gained weight slightly more (P >0.05) than Horro lambs (69.43 ± 1.58 g for Menz and 68.14 ± 1.83 g for Horro). Average daily weight gain of Horro lambs observed at all stages of growth was much lower than what is reported else where (Table 5). The Menz have attained about 25 % of the estimated mature weight of the breed compared to about 22 % for the Horro. It is important to note here that the low pre-weaninig and post-weaning growth rate of the lambs of both breeds seem to be far from their potential level. This indicates a possible genotype x environment interaction as Horro lambs have shown a better performance in their area of origin (Table 5) where Gojjam et al. (1998) have reported a pre-weaning average daily weight gain of over 130 g.

After weaning, the growth rate of both breeds dropped substantially and then improved slightly. As shown in Figure 6, Horro lambs had a slightly better growth rate (P <0.05) between 270 and 365 days of age than Menz lambs.

The two breeds had an average daily weight gain of less than 30 g between weaning and 180 days of age (Tables 14 and 15). As shown in Figure 1, Horro lambs have tended to be heavier than Menz lambs at all stages of growth between 60 and 180 days of age though not significantly different (P >0.05). This trend was unchanged when only male lambs were considered (Table 13 and Figure 2). From 270 to 365 days of age however, Horro lambs gained significantly more weight (P <0.05) than the Menz (57.36 ± 3.17 g vs 50.62 ± 2.20 g, respectively).

The effect of breed on birth weight and subsequent growth performance of lambs is well documented. The early stages of growth are known to be strongly influenced by breed size, milk producing ability of the dam, the environment under which lambs are maintained, notably availability of adequate feed supply (Bathaei and Leroy 1996, Burfening and Kress 1993, Gatenby 1986, Notter and Copenhaver 1980).

As indicated in Table 12 Horro lambs were heavier (P <0.001) at birth compared to Menz lambs and this could be mainly due to their relative bigger body frame than the Menz. However, despite their relative advantage of being adapted to the area, Menz lambs did not grow faster (P >0.05) than the Horro since Horro ewes have been brought from a highland location of warmer climate.


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The weaning weights (at 90 days of age) of both Menz and Horro lambs reported here (8.03 ± 0.12 kg for Menz and 8.21 ± 0.13 kg) are lower than weaning weights reported for the same breeds in their respective area of origin (Table 4). The reason for lower weaning weight of Menz lambs investigated under station condition could be due to differences in management and probably due to a heavier internal parasite load, as lambs in this study were drenched to control mostly Fasciola. On the other hand the reason for the Horro lambs to have a lower weaning weight than that reported else where could be due to adaptation problems in addition to internal parasite problem other than liver fluke.

Vercoe and Frisch (1987) have stated that the nature of the relationship between high growth potential and low resistance to environmental stresses should be determined in order to alleviate problems associated with the development of economically productive breeds which are also tolerant or resistant to environmental stresses. The production environment under which Menz and Horro lambs have been maintained in this study, therefore, could not be described as stress free as the animals were also regularly subjected to other studies through faecal sampling, blood sampling, etc. The low body weight of both Menz and Horro lambs could, therefore, be due to other external factors rather than the inherent potential of the breeds.

If lambs could be maintained under better management practices, economically productive animals could be selected by using their weaning weight in a selection index (van Wyk et al. 1993). The authors have suggested that an animal's weaning weight indicates its value at the desired marketing age.

Body weight of Menz and Horro lambs at 6 and 12 months of age is much lower than that reported in their respective area of origin by others (Table 4). This could mostly be due to differences in management although possible breed variation in growth rate could not be ruled out. As indicated in Tables 4 and 5, lamb growth patterns are influenced by the type of production systems practised. Such disparity in body weight development indicates that there is scope for improvement. On the other hand Notter et al. (1991) have reported that lamb growth rates could not be equated directly to the profitability of a certain production system since systems that promote an accelerated lamb growth mostly attain a high level of weight gain efficiency on the biological scale (kg gain/kg feed). This is realised under a more intensive type of production which requires supplementary feeding and this in most cases is beyond the reach of farmers in the tropics and sub-tropics.

At 12 months of age, Horro lambs were significantly (P <0.05) heavier than the Menz and this could be as indicated earlier due to the increase in size rather than improvement in body condition.


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Male lambs maintained their weight superiority at birth compared to females until 180 days of age (Table 12 and Figure 3) which was significant (P <0.01) at all stages. After the age of 180 days, female lambs received a preferential treatment for a different experiment. Therefore, it was not possible to continue the comparative evaluation of body weight development between male and female lambs.

When the rate of weight gain of only male lambs is considered (Table 15), Menz lambs seem to have faster (though not significantly different) preweaning (birth to 90 days) and post-weaning (90 to 180 days) weight gain compared to Horro lambs.

The effect of birth type is consistent with other reports in the literature. The influence of birth type on growth performance is well documented by Tuah and Baah (1985). In this study as well, lambs born as singles had maintained their weight superiority at birth throughout the study period (Tables 12 and 13). Single born lambs were not only heavier at all stages of growth, they also had a higher pre-weaning rate of weight gain compared to twins. Single born lambs had average daily gains of 109.06 ± 1.65 g, 81.34 ± 1.34 g and 25.50 ± 0.86 g between birth and 30 days, birth and 90 days (weaning) and between weaning and 180 days respectively. The corresponding figures for twins are 69.41 ± 2.87 g, 56.23 ± 2.14 g and 26.96 ± 1.65 g, respectively. Single born lambs and twins were not significantly different (P >0.05) in post weaning average daily weight gain (Table 14). This confirms the influence birth weight, which is also related to birth type, has on subsequent growth performance of lambs. In areas where there is seasonal fluctuation in availability of fodder, it might be advantageous to aim for maintaining fast growing single born lambs that could reach marketable weights in the shortest possible time rather than attempting to improve prolificacy of ewes to increase the number of lambs born per parturition.

Dam parity had strongly influenced body weight at all stages of growth (Tables 12 and 13). This influence was more pronounced between birth and 30 days of age as well as between birth and weaning, where lambs from second parity ewes had higher (P <0.001) rates of daily weight gain than those born from first time lambers (98.07 ± 2.09 g vs 80.40 ± 2.21 g, respectively). The same was true when only male lambs were considered. Male lambs from second parity ewes were not only heavier at all stages of growth, they also had a higher rate of weight gain between birth and 30 days of age compared to lambs from first parity ewes (101.38 ± 3.27 g vs 83.66 ± 3.72 g, respectively). This could be due to a better mothering ability and milk production of multiparous ewes compared to first time lambers. A similar result was obtained from a study on Caribbean sheep breeds (Rastogi et al. 1993), where it was observed that the influence of mothering ability on average daily weight gain and weaning weight had been highly significant.


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Lambs born into the wet season (Table 12) had a better pre-weaning growth performance compared to the other two groups. This could be also due to the availability of quality pasture at lambing time. Although the third group of lambs (Dry'93), were born at about the same period of the year as those in group one, their body weight (except that of birth and at 30 days of age) was significantly lower than the others (Tables 12 and 13). This could probably be due to the build up of internal parasite load rather than feed shortages as this group also had the lowest rate of survival (Table 16) at all stages of growth compared to the other two groups. As shown in Figure 4, male lambs born in the first group (Dry'92) had a relatively better growth performance compared to those male lambs born in Wet'93 and Dry'93 lambing seasons probably due to lesser parasite challenges in the first season.

However, the result shows no clear distinction between the effects of the two major lambing seasons (lambing into the wet season and into the dry season). Lambs born in the third season (Dry'93), which is supposed to be a replication of the first (Dry'92), had a much lower (P <0.05) growth rate between birth and weaning compared to Wet'93, and even Dry'92, lambs. As Dry'93 lambs were born from the same ewe flock as Dry'92, the reason for their relatively poor performance could most probably be environmental stresses.

Where extensive grazing is used to rear small ruminants like in most tropical and sub-tropical countries, one way of reducing the impact of seasonal forage shortage is a careful management plan. This could be in the form of planning the mating period so that ewes could drop their lambs during the time of the year when there is a relatively better provision of feed. The other alternative could be reducing the number of non productive animals if that is culturally accepted.

Seasonal fluctuation in feed availability causes animals to pass through weight gain/weight loss phases (Velez et al. 1993, Ehoche et al. 1992). In another study, Wilson (1987) has reported that very little is known about factors influencing weight of small ruminants in sub-Saharan Africa. However, since his work involves only Malian sheep, which seem to be not affected by fluctuations in seasonal feed availability, this might not be true for other tropical or sub-tropical breeds.

As there are several assumptions regarding factors affecting growth of grazing animals in tropical countries, growth potential of animals in such environments could be better estimated by keeping the animals to be studied in pens (Vercoe and Frisch, 1987). The authors also assume that since growth potential is associated with low resistance to environmental stresses, it will be of paramount importance to first determine the nature of the relationship between the two. This might help to enhance the development or identification of breeds that might be tolerant or even resistant to environmental stresses and which could also be economically productive.


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Pre-weaning average daily weight gain and weaning weight of animals are known to be strongly influenced by the mothering ability of the dam as young animals before weaning are more dependant on the dam's milk yield rather than foraging. In this respect it seems that Menz and Horro ewes seem to have no significant difference as their lambs had relatively similar pre-weaning growth rates (Tables 14 and 15).

Results from other studies (Laes-Fettback and Peters, 1995, Rastogi et al. 1993) show that the pre-weaning daily weight gain and body weight of the offspring to be significantly influenced by breed and mothering ability. However, careful considerations have to be made in implementing comparative breed evaluation particularly when breeds are exposed to new ecosystems for which they might have difficulties to adapt and acquire tolerance if new disease challenges occur. The relative poor performance of Horro sheep, compared to what is reported elsewhere (Solomon Abegeaz, 1998; Yohannes Gojjam et al., 1998) could be seen in this perspective. It can not be excluded that the Horro ewes were under severe biotic stress at the experiment station since a number of ecological factors differ from their original habitat.

In a sheep production system where the main objective is lamb meat production, post weaning growth rate of lambs is just as important as the pre-weaning growth rate. It is also in this stage that animals are subjected to various environmental stresses starting with the so called weaning shock to seasonal variation in feed availability. This is particularly evident in the dry tropics where growth curve is expected to be highly irregular due to weight gain/weight loss phases depending on the availability of forage both in terms of quantity and quality. In such situation it might be advantageous, as Gatenby (1986) suggested, to keep small size breeds which could grow as fast or even better than larger breeds.

4.4.3 Lamb survival rate

Both Menz and Horro lambs have differed significantly in survival rate from birth to various stages of growth except the period within two weeks of birth as shown in Table 16. High proportion (P <0.05) of Menz lambs born have survived to 30 days of age compared to Horro lambs (95.5 ± 0.02 % vs. 91.2±0.02 %, respectively). As the lambs grow, the difference in survival rate between the two breeds was even more pronounced (P <0.001). The survival rates of lambs of those born to 90 (weaning age), 180, 270 and 365 days of age were 89.4, 81.3, 71.5, 62.4 % for Menz and 75.7, 50.6, 39.0, 37.3 % for Horro lambs, respectively.


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As sheep production is directly influenced by the number of lambs born and reared from a flock at a given time, it is highly important to identify the causes of lamb losses and take the appropriate measure to reduce it. There will be none or very little advantage in increasing the productivity of the existing ewe flock or introducing prolific breeds without taking the appropriate measures needed to minimise both prenatal and postnatal lamb mortality. Mukasa-Mugerwa and Lahlu-Kassi (1995) have reported that high lamb losses nullify the efforts made to improve the productivity of ewe flock. In another study, Gatenby (1986) has reported that prenatal lamb losses could be greatly reduced by improving management practices.

As shown in Figure 8, the survival rate of Horro lambs drastically decreased after 90 days of age (weaning) and only about 50 % of Horro lambs have survived to 180 days of age. This could be a reflection of environmental effects rather than inherent breed differences in survival rate as the Horro has been brought from a different ecosystem with different humidity, temperature and above all a different disease challenge.

Effects of sex, birth type and dam parity on survival rate are consistent with results from other studies where it was reported that males, single born lambs and lambs born from multiparous ewes had a better survival rate compared to females, multiple born lambs and lambs born from ewes of first parity respectively (Gatenby et al.1997, Armbruster et al. 1991, Notter et al. 1991). As shown in Table 16, twin lambs had a significantly low (P <0.001) pre-weaning and post weaning survival rate. The survival rate of single born lambs to weaning and to 180 days of age was 91.4±0.01 % and 82.6±0.02 % while the corresponding figure for twins was 71.2 ± 0.04 % and 48.4 ± 0.04 %, respectively.

Lambs born to ewes of second parity had a significantly better pre-weaning survival rate of about 90 % compared to about 75 % for those born to first time lambers (Table 16). This is could well be a reflection of a better mothering ability of the relatively older ewes compared to the first time lambers. The low post weaning survival of lambs born to ewes of first parity compared to those born from second parity ewes could be due to the combined effects of weaning shock and other environmental stresses like poor pasture quality and disease challenges.


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Fitzhugh and Bradford (1983) have reported a reduction of lamb mortality from 23 % to 11 % by improving ewe nutrition during the gestation period. If proper management considerations are not taken, poor nutritional and physiological status of ewes during gestation period results in the birth of weak lambs with low birth weights. As indicated by Fitzhugh and Bradford (1983), ewes in such circumstances will have poor milk yield to feed their lambs leading to a high lamb mortality, particularly within the first two weeks of birth. The relationship between birth weight and mortality has been known for long. Several studies have indicated that birth weight has a quadratic type of relationship with mortality rate whereby lamb mortality tends to increase at extremely high or extremely low birth weight ranges (Mendel et al. 1989, Cooper 1982, Notter and Copenhaver 1980). In another study on goats Laes-Fettback and Peters 1995, have observed that survivability and the pre-weaning growth rate of goat kids are strongly influenced by birth weight.

Apart from low birth weight, causes of early lamb losses occurring within five days after birth could be birth stress, birth injuries, organ malfunctions, starvation or miss-mothering (Bullerdieck, 1996). Planning to make ewes lamb in groups within a narrow time frame will hamper the attention given to both ewes and lambs at lambing thus enhancing management induced miss-mothering and resulting in high neonatal lamb losses (Bullerdieck, 1996).

Table 16 shows that lambs born into the main rainy season and weaned at the end of the wet period (Wet'93) had relatively higher post-weaning survival rates compared to the other two groups (Dry'92 and Dry'93). One possible reason could be that this group was weaned at the end of the rainy season when there is still relatively adequate forage. On the other hand, group one and group 3 lambs were weaned in the dry season and their relative poor performance could be attributed to this. The extremely low post weaning survival of lambs born into the Dry'93 season compared to those born into the previous dry season (Dry'92) indicates that the former probably had a higher parasitic and disease challenges.

As the summary of breed performances (Table 6) in various areas indicate, the type and level of management followed greatly influences the survival of lambs, most importantly during the prenatal growth stage.

Linear body measurements and their relation to changes in body weight, body conformation and body composition

Qualitative body measurements will be more useful whenever it is difficult or impossible to take quantitative measurements. Besides, qualitative measurements could also be used as indicators of changes in body conformation of animals over a given life span (El-Feel et al. 1990). As shown in Tables 18 and 19, male Horro and Menz lambs were significantly different in wither height at 9 and 12 months of age (p <0.01 and p <0.001, respectively) when Horro lambs were taller at withers than the Menz. Although not significantly different (p >0.05), male Menz lambs had a wider heart girth measurements at all stages compared to the Horro. This partially explains the physical differences of the two breeds where Menz sheep are deep bodied with rather short body and short legs indicating that the Menz is a compact breed probably with medium growth capacity. On the other hand, the Horro are tall and long bodied sheep with rather long legs and medium chest circumference probably with a relatively higher growth capacity.

Deviation of the linear body measurements from the overall LS Means as shown in Figures 9, and 10 indicate that as the lambs grow, their differences in wither height, body length and particularly the differences in tail length seem to get wider.

Linear body measurements could also indicate the changes in body proportion (Arthur and Ahunu, 1989). According to Arthur and Ahunu (1989), body size, as measured by weight, does not tell much regarding differences and fluctuations in body proportion caused by weight loss and gut fill.

Correlation coefficients among the various linear body measurements and live body weight of Menz and Horro lambs at 6, 9 and 12 months of age were strong and positive as shown in Tables 20, 22 and 24, respectively. Relationship between live body weight and heart girth has long been used to estimate the former from measurements of the latter. If there exists a positive and significant relationship between weight and linear body measurements like heart girth, wither height, etc., it could be possible to identify a relatively smaller number of factors which could be used to describe the relationship by doing principal component analysis of the body measurements considered (Arthur and Ahunu, 1989). According to Brown et al. (1973), such techniques could also be used to compare animals of different shapes and sizes.


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4.4.4 Fattening performance, feed intake and weight gain

Since the supply of animal feed in the tropics is not constant in terms of both quantity and quality, particularly in arid and semiarid regions, one observes seasonal fluctuation in growth rate of animals in theses regions (Gatenby, 1986). This is particularly true in Sub-Saharan Africa where the main source of animal feed is grazing on natural pasture. To make use of whatever resource is available more economically, it will be advantageous to identify those breeds of animals which are more efficient meat producers (Terrill and Maijala, 1991) or animals which have high performance in feed conversion efficiency to produce saleable products (Parker at al. 1991).

Although Horro lambs were heavier at the end of the 123 days fattening period and also had a heavier slaughter weight than the Menz, Menz lambs had a relatively a better dressing % though not significantly different (P >0.05). This could be an indication showing that Menz are relatively early maturing sheep compared to Horro. As shown in Table 27, the relatively higher carcass moisture loss for Horro lamb carcasses (4.2 %) compared to that for the Menz (3.8 %) indicates that Menz lamb carcasses have a better fat cover than the Horro.

During the feeding experiment, Horro lambs consumed more (p <0.01) total dry matter daily compared to Menz lambs which were 879 ± 12.27 g vs. 802 ± 9.35 g respectively (Table 29). Several authors (van Arendonk et al. 1991, Barlow et al. 1988, Wagner et al. 1986) have reported the existence of breeds or genotypes differences in feed intake. The difference in feed intake between breeds is also reflected in the gut content. As reported by Ruvuna et al. (1992), gut content constitutes about 14-18 % of live weight. This is also conformed in the present study where the observed gut content as proportion of the slaughter weight was 15.2 ± 0.50 % for Horro and 13.2 ± 0.45 % for Menz (Table 24), the differences between the two being significant (P <0.01).

Although Horro lambs seem to have a high dry matter intake per kg W0.75, (67.8g for Horro lambs and 65.6 g for the Menz), though not significantly different (P >0.05), the faecal dry matter estimate for Horro lambs was also significantly higher (p <0.01) than that for Menz lambs (Table 29). It is therefore assumed that Horro lambs might have relatively poor feed retention ability than Menz lambs. This is also reflected in the digestibility estimate of feed for the two breeds whereby Menz lambs seem to have a better digestibility estimate (p <0.01) than the Horro (Table 29).


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In some other studies (Khandaker et al. 1998, Dulphy and Demarquilly, 1994, Wagner et al. 1986), it was reported that the daily feed intake of animals is influenced by the digestion rate of the digestible materials of the feed and the rate of passage of the indigestible part. In another study (Zervas et al. 1997), it was stated that dry matter intake by lambs was influenced partly by the nature, energy and nutrient density of the available feed. Dulphy and Demarquilly (1994) have also reported that voluntary feed intake of ruminants is determined by the ingestibility of the feed and the intake capacity of the animal. However the information regarding to the extent of the variation between breeds in this trait is very limited.

Feed intake is also closely correlated with the quantity of pasture available per head per day and the quality of the forage selected in terms of digestibility (Said and Tolera,1993, Black, 1990). In another study Mehrez et al. 1977 have reported that feed intake could be reduced if rumen ammonia concentration is limiting the feed fermentation rate in the rumen. It is not the type and physical characteristics of feed that influence its intake rate but also the animal's age, size, weight and physiological status and the prevailing climatic conditions (Arnold and Birrel, 1977).

In a study on some pure and crossbred sheep in Morocco (Kabbali et al. 1992), a better feed efficiency was observed in those animals which have gone through a weight loss and weight gain (compensatory growth) phase. The relatively high availability of green feed in tropical regions during wet seasons is thought to enhance body fat deposition. According to Ørskov (1998), ruminants are capable of adapting to seasonal fluctuations in forage availability in terms of both quantity and quality and conserve energy from the lush period in the form of body fat. The author has suggested that fat deposition generated by high quality pasture intake could even be an efficient form of conserving forage to be mobilised to sustain growth, lactation or maintenance requirements. Such ability of sheep to retain and then mobilise body reserves will be of paramount importance particularly in arid and semiarid environments for their productivity and survival (Frutos et al. 1997).

4.4.5 Relative weight of carcass and non-carcass components and dressing percentage

The higher, though not significantly different (P >0.05), dressing % for Menz lambs (49.1 ± 0.57 %) compared to Horro (48.0 ± 0.64 %), could indicate that Menz lambs have advanced relatively nearer to slaughter maturity than the Horro. The value of carcasses is mostly determined by the lean (muscle) : bone ratio (Anous, 1991).


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Proportion of muscle, fat and bone change as animals grow whereby the growth of bone reaches its peak first followed by muscle and adipose tissues respectively (Orr, 1982). This has also been conformed by Afonso and Thompson (1996) and Taylor et al. (1989). In both cases it was stated that relative to empty body weight, bone tissue matured early followed by muscle (lean) and fat tissues. There was no significant (P >0.05) difference observed between Menz and Horro lamb carcasses in dissectible lean and fat tissues (Table 27). However, Horro lambs had higher (P <0.01) estimated total bone weight compared to that of the Menz. When only the carcass components of the dissected left half carcasses are considered, there were no significant differences in proportions of carcass components between the two breeds (Table 28). The lean : fat : bone ratio observed in this study (3.1 : 1 for Menz and 3.3 : 1 for Horro lamb carcasses is within the range reported by several authors (Table 8) for various tropical and temperate breeds.

Since the management under which the various breeds were maintained and the age at which the animals were slaughtered vary considerably, it will not be appropriate to make direct comparison. However, the carcass composition of Menz and Horro lambs as observed in this study seems to be more or less in line with what is reported particularly for tropical breeds (Table 8). As reported by Anous (1991) and Taylor et al. (1989) muscle (lean) : bone ratio is the most critical determinant of carcass value. Since lean is the most important economic component of carcass in any meat production enterprise, the higher its ratio the better. The lean : bone ratio observed (Table 29) in this study for Menz and Horro lamb carcasses (2.8 : 1 and 2.6 : 1, respectively) for the dissected half carcasses was higher than that reported by Enyew Negussie (1999) which is 2.5 : 1 for Menz and 2.2 : 1 for Horro , (P <0.0001). The lean : bone ratios observed in this study for the two breeds were also significantly different (P <0.05), indicating that carcasses from Menz lambs tend to have a higher lean : bone ratio compared to Horro. One possible explanation for the differences in lean : bone ratio in the two studies could be that Menz and Horro lambs in the present study were slaughtered at a relatively older age (about 17 months) while those studied by Enyew Negussie (1999) were slaughtered at about one year of age and without any prior fattening.

There is evidence (Ruvuna et al. 1992) that proportion of lean and fat increase with age while the proportion of bone decrease. A similar result was obtained in an earlier study by Berg and Walters (1983) where it was reported that the ratio of fat to muscle and that of muscle to bone increased with age. This means that as animals mature they tend to deposit more fat than muscle. The slightly higher, though not significantly, fat to lean ratio for Menz lamb carcasses (0.34 : 1, respectively) compared to that of the Horro (0.31 : 1, respectively) could be an indication showing that Menz sheep are earlier maturing than Horro. However, according to Taylor et al. (1989) it is indicated that there might be no significant breed differences in lean (muscle), fat and bone distribution as affected by age.


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Moisture loss in carcasses observed in this study (3.8 ± 0.17 % for Menz and 4.2 ± 0.19 %, P >0.05) is higher than that reported for castrated goat carcasses (1.6-1.9 %) by Ruvuna et al. (1992). A slightly lower (2 %) moisture loss or shrinkage of lamb carcasses has been also reported by Thompson et al. (1987) after a 24 hour storage.

Kempster et al. (1981) have reported a moisture loss of 2.27 % in pig carcasses after a 24 hours storage time. It is suggested that such information will help to account for the weight loss of hot carcasses between the point of slaughter and after a limited storage time. Therefore, the loss of carcass weight at storage for carcasses with higher fat cover could be less than carcasses with lower fat cover.

In another study (Farid, 1991), it was concluded that the relative merit of different sheep breeds for meat production is determined by a higher proportion of lean and low proportion of fat and bone in the carcasses. While this is very true for markets in developed countries, animals with a higher degree of fat cover, regardless of size and weight, fetch a higher premium in most tropical countries (Thatcher and Gaunt, 1992, Terril and Maijala, 1991, Lee 1986). This is particularly true in Ethiopia where during festivities, lambs and withers with high fat cover are priced highly.

On the other hand the characteristics of a superior carcass in developed countries are high proportion of muscle (lean), low proportion of bone and an optimal level of fat cover (Taylor et al. 1989). The fact that the lean proportions of carcass is strongly influenced by breed, sex and stage of maturity or mature size of the animal is well documented (Taylor et al. 1989). Based on the preliminary result in this study, Menz and Horro lambs seem to differ in carcass lean and bone composition. It might be, therefore, possible to compare the two breeds at similar stages of maturity to establish the extent of breed influence on body composition.

Lean and fat are not mutually exclusive traits. In fact Berg and Walters (1983) have reported that a higher fat proportion is associated with a lower proportion of muscle and vice versa (see Table 8). According to Berg and Walters (1983), the proportion of muscle to live weight could be a useful index to select meat producing animals for higher carcass yield. In this study, Horro lambs had a higher proportion of lean to empty body weight (38.6 %) compared to Menz lambs (35.9 %). In another study Walstra and de Greef (1995) have stated that the proportion of lean in carcasses could be also influenced by carcass weight, dissection and lean mass measuring methods and procedures.


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4.4.6 Fat deposition characteristics

Body composition in terms of both dissectible components (muscle, fat and bone) and chemical composition such as chemical fat, protein, ash and water change as animals grow from birth to maturity (Enyew Negussie, 1999, Snowder et al. 1994).

Carcass composition could be used as a tool to characterise breeds for possible identification of potential genetic resource for lean lamb production and also to identify management alternatives to suit different breeds (Snowder et al. 1994). Since breed is known to influence not only carcass composition and quality but also carcass conformation as well, differences in carcass merits between breeds is likely to govern the choice and development of breeds for specific production objectives. Apart from breed, carcass composition is also known to be influenced by sex (Cantón et al. 1992).

The major non genetic factor influencing carcass composition is nutrition. Several authors working on various breeds and species under various management and environmental conditions have observed that nutritional level and feeding regime have affected carcass yield and quality, fat tissue development and composition (Iason and Mantecon 1993, Cantón et al. 1992, Cronjé and Weiter 1990, Gatenby 1986).

The fact that breeds differ in dissectible carcass composition has been cited from various sources by Enyew Negussie (1999) where it was reported that breeds do not only differ in carcass components (muscle, fat bone) but also in their distribution. In this study no significant differences (P >0.05) was observed between Menz and Horro sheep carcasses in the estimated whole carcass composition of lean and fat after the 123 days of fattening. However, the two breeds have differed significantly (P <0.01) in the estimated total bone composition of whole carcasses (Table 30).

The whole carcass composition estimate was based on the observed dissectible half carcass composition. Whole carcass composition estimates of 58.0 %, 19.5 %, 20.4 % and 2.1 % lean or muscle, fat, bone and sundry in Menz and 57.9 %, 18.0 %, 21.5 % and 2.6 % in Horro, respectively were not significantly different (P >0.05). However, the figures show that Menz lamb carcasses tended to contain more fat (P >0.05) than carcasses of Horro lambs. The carcass proportion found in this study was not very much different from that reported by Gruszecki et al. (1994) for Polish lowland sheep and its crosses slaughtered between 38 and 40 kg (61-63 % lean, 17-20 % fat and 19-22 % bone). In another study (Streitz et al. 1994) a carcass composition of 58.2 % lean and 23.6 % fat was reported for mutton type lambs of diverse genetic background which had above 30 kg live weight at slaughter.


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Taylor et al. (1989) have reported that larger breeds have higher proportions of carcass fat compared to smaller sized breeds. The authors have also observed a carcass composition of 58.3 % lean, 24.3 % fat and 17.4 % bone for seven British sheep breeds. A similar observation was also made by Teixeira and Delfa (1994) who reported a carcass composition of 55.5 % and 55.7 % muscle, 23.8 % and 24.1 % fat and 16.0 % and 15.7 % bone for Suffolk and Merino sheep carcasses, respectively. In contrast, El Karim and Owen (1987) have reported a carcass composition of 58-59 % lean, 14-16 % fat and 18-20 % bone for one year old Egyptian sheep weighing between 25 and 34 kg. The carcass composition observed in this study for the dissected part is in line with that reported by El Karim and Owen (1987) for one year old Egyptian sheep breeds which were slaughtered within the same body weight ranges as that for Menz and Horro lambs in the present study.

Although it is reported (Gaili, 1979, Gatenby, 1986) that tropical sheep tend to deposit more intramuscular and internal fat and less subcutaneous fat compared to temperate mutton breeds, there is evidence (Amegee, 1981 cited by Gatenby, 1986) that tropical and temperate breeds also differ in size and distribution of fat deposited in the body but not in their carcass composition.

4.4.7 Fat depot distribution in Menz and Horro lambs

It has been known for long that breeds and species differ in fat depot partitioning. According to Frutos et al. (1997) and Kempster (1981), sheep breeds developed for fat lamb production deposit more subcutaneous fat than those sheep breeds which are kept in areas where adaptability and maternal performance play a role in influencing productivity.

Fat depot distribution characteristic of the two breeds was measured directly by physical separation of dissectible fat from carcass and non-carcass components as well as indirectly by chemical analysis through ether extract. Tables 33 shows fat depot estimates for whole carcass components based on sample ether extract of the dissected part.

The result in this study shows that the two breeds differ significantly (P <0.05) in total ether extract estimate (3059.5 ± 95.20 g for carcasses from Menz lambs and 2718.70 ± 106.60 g for Horro lamb carcasses). The higher (P <0.01) ether extract estimate on dry matter basis for lean from Menz lamb carcasses (22.4 ± 0.89 %) indicates a higher proportion of intra- and inter-muscular fat compared to that of the Horro (18.1 ± 1.00 %). This indicates that carcasses from Menz sheep are also qualitatively better than those from the Horro as marbling is a sign of qualitative measure. However, Menz and Horro lambs did not differ significantly (P >0.05) either in their fat deposition characteristics or fat depot distribution (Tables 33). In both breeds, the biggest proportion of fat depot was the sum of subcutaneous fat and the separable intermuscular fat.


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The relatively high fat proportion in Menz lamb carcasses is also an indication that it is closer to maturity compared to the Horro. Since the Menz are shorter but relatively wider sheep than the Horro, they have a relatively better conformation. On the other hand, Horro sheep are relatively larger but have more bone and less flesh compared to the Menz and are likely to take longer time to reach slaughter maturity with acceptable carcass fat cover.

The next highest fat depot concentration in both breeds was the tail and around the rump area. Horro had slightly higher but not significantly different (P >0.05) proportion of rump and tail fat compared to Menz (30.8 % vs 29 %). The third and fourth highest concentration of fat for both Menz and Horro lambs was observed to be as intramuscular fat and Gastro-Intestinal-Tract (GIT) fat, respectively (Table 33). The least proportion of fat depot for both breeds was around the urogenital area. However, in all cases both breeds were not significantly different (P >0.05), though Menz lambs tended to have more fat depot in most parts except the tail and rump region. This is in agreement with the results obtained by Enyew Negussie (1999) in a study on the same breeds where it was observed that generally Menz lambs tended to have more body fat compared to Horro slaughtered at about the same age and stages of growth.

The carcass composition of the dissected left half carcasses in the present study (Table 28 and Figure 11) show a relatively higher proportion of lean than that interpolated for whole carcasses (Table 27). Though not significantly different (P >0.05), carcasses from Horro lambs tended to have higher proportion of lean (muscle) and bone than Menz lamb carcasses (Table 28). Due to the exclusion of tail fat from the dissected part, the proportion of fat in the left half of carcasses seems to be smaller than that estimated for whole carcasses.

The fact that fat is the most variable body tissue has been well documented (Negussie, 1999, Berg and Walters, 1993). Fat deposition is strongly influenced by genetic factors such as size and maturity and also by non genetic factors such as age or stage of maturity and by nutrition. Fat reserves or deposits influence meat quality and could also determine the survival of animals, particularly those in the tropics during periods of acute or prolonged feed shortages. In a study by Cantón et al. (1992) it was reported that nutrition influences carcass yield and quality, fat deposition and composition while breed effect was observed to be greatest in influencing carcass conformation as well as carcass composition. The authors have also indicated that hair sheep deposit more non-carcass fat internally (mesenteric, kidney knob and channel, et.) than wool sheep which in turn have a higher subcutaneous fat depot. This is also conformed in this study where Menz lambs, which are coarse wool bearing sheep, had relatively higher proportion of subcutaneous and intermuscular fat though not significantly different (P >0.05) compared to the Horro which are hair sheep. According to Kempster (1981), the fat depot distribution is also related to adaptability where he observed that animals kept under harsher hill environment tended to have higher internal fat depot.


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In the present study, Menz lambs which are adapted to a harsher highland environment of Shewa region in Ethiopia tended to have relatively a higher amount of mesenteric and renal fat depots though not significantly different (P >0.05) than that of the Horro which originate from warmer and humid western highlands of the country.

Another factor known to influence carcass composition is the degree of maturity. Friggens et al. (1994) and Iason et al. (1992) have stated that maturity is an important predictor of carcass composition, particularly for some European breeds. In both studies it was observed that large breeds of sheep attain their maturity at a relatively older ages than smaller ones. It is, therefore, recommended (Iason et al. 1992) that such different groups should be compared at a similar proportion of mature live weight to avoid or minimise the differences in carcass composition arising from differences in maturity stage. A study by McCutcheon et al. (1993) supports such a recommendation where it was observed that carcasses of similar body weight showed similar proportions of water, protein and fat.

In contrast to what Negussie (1999) observed in his study on Menz and Horro lambs, the present study showed no significant differences in either fat deposition or fat distribution between the two breeds. He has also observed that Horro lambs had deposited relatively more internal fat than the Menz. However, this was not realised in the present study. In fact Menz lambs tended to have deposited more carcass and non-carcass fat as indicated in both the ether extract estimate for whole carcasses and various fat depots as shown in the dissected left half carcass composition (Table 32).

The relatively higher (P <0.01) ether extract of lean for Menz (22.4 %) compared to that of the Horro (18.1 %) indicates that Menz lamb carcasses have more inter- and intramuscular fat compared to that of the Horro (Table 33). As indicated by Frutos et al. (1997), individual breeds have a distinctly different fat distribution within the body. This result also indicates that Menz and Horro lambs seem to differ in body fat distribution. However, a more detailed investigation will be required to draw any conclusive results.

No matter in which way sheep deposit fat, their ability to retain and mobilise body reserves, particularly in arid and semiarid areas of the tropics where feed resource is a limiting factor, it will be of paramount importance to determine their productivity or even their survival. For such reasons, it will be useful to be able to determine body composition of animals particularly those maintained under extensive systems using the most simplest available methods as slaughtering will be expensive. One such method could be using leaner body measurements to estimate body composition. An attempt has been made to estimate tail fat weight using live tail volume measurements (Tables 34, 35 and 36).


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The linear regression analysis (Table 36) show that in both breeds, total body fat could be fairly accurately estimated from tail weight and tail volume measurements. Since Horro is the larger of the two and since it has a relatively larger tail this might be an indication of the breeds characteristics in depositing body fat. Menz is also a fat tailed sheep but the size of the tail is relatively smaller than that of the Horro. However, further detailed investigation has to be made to reach a conclusive result since the data used for the current analysis is very limited as to whether tail measurements could be reliably used to estimate total body fat.

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