|Awgichew, Kassahun: Comparative performance evaluation of Horro and Menz sheep of Ethiopia under grazing and intensive feeding conditions |
Keywords: Sheep, breed, characterisation, lamb, bodyweight, growth rate, survival rate, linear body measurements, carcass performance, fat deposition, body fat distribution, Ether extract
This study has been carried out at the former International Livestock Centre for Africa (ILCA), that is now the International Livestock Research Institute (ILRI) experiment station at Debre Birhan, Ethiopia.
This research is part of an ILCA (now ILRI) Pan-African research programme designed to investigate and characterise genetic resistance to endoparasites in some indigenous small ruminants in sub-Saharan Africa. The present study was, therefore, undertaken in an attempt to generate information that may contribute towards the understanding of the relative performance of two highland sheep (Horro and Menz) of Ethiopia under station management conditions.
Ewes were randomly divided into two groups to have dry season (October/November) and wet season (June/July) lambings. A total of 984 lambs (396 Horro and 588 Menz) were born over the three lambing periods (Dry'92, Wet'93 and Dry'93) covered by this study. However, due to differences in parity between ewes of the two breeds, where there were some Menz ewes which had lambed three or more times earlier, lambs born from such ewes were excluded from this study. Therefore, only 856 lambs born from first and second parity ewes of both breeds were included. Ewes and lambs were herded together until weaning at the age of about 90 days. Weaned female and male lambs were separated but were exposed to the same grazing paddocks in a rotational grazing system.
In addition to grazing, hay was offered ad libitum while concentrate was group fed at the rate of about 200 g per day providing 10-12.5 MJ ME/kg dry matter.
All flocks were routinely checked for any health problems and treated accordingly. Flocks were also drenched with FasinexR (triclabendazole) against Fasciola towards the end of the rainy season and in the middle of the dry season.
111Male lambs born in the first lambing season of the program (Group one) were put into a fattening experiment at the age of about 12 months. During the fattening experiment, lambs were individually fed in metabolic crates. Hay was provided at the rate of 1500 g per day throughout. On the other hand concentrate supplementation was done in stages where lambs were given 300 g per day for the first two weeks including the two week adaptation period. The concentrate level was then raised to 400 g per day and this level was maintained until the end of the fattening experiment.
Horro lambs were significantly heavier (P <0.001) at birth than Menz lambs (2.43 ± 0.03 kg vs 2.17 ± 0.03 kg, respectively). Apart from breed, the other main effects which have influenced birth weight significantly (P <0.001) are sex, type of birth, dam parity and season of birth. Lambs born in the dry season from ewes mated at the beginning of the wet season tended to be heavier at birth than those born from ewes mated in the dry season. This is assumed to be linked to the availability of relatively better pasture in terms of both quality and quantity during the ewe's gestation period.
While there was no significant difference in weaning weight between Menz and Horro lambs (8.03 ± 0.12 kg vs 8.21 ± 0.13 kg, respectively), sex, birth type, dam parity and season of birth have all significantly (P <0.001) influenced weaning weight. Sex, birth type and season of birth remained to be significant sources of variation in body weight of male lambs of both breeds until one year of age.
The two breeds did not differ significantly in average daily weight gain between birth and weaning (90 days). Birth type, dam parity and season of birth have significantly (P < 0.01) influenced pre-weaning average daily weight gain (ADG). Single born male lambs gained 114.62 ± 2.58 g and 82.42 ± 1.85 g daily between birth and 30, birth and 90 days of age, respectively. The corresponding figures for twin born male lambs are 71.71 ± 4.53 g and 55.75 ± 3.34 g, respectively.
112Lambs from second parity ewes had a higher rate of weight gain between birth and 30 days of age and between birth and weaning (90 days) compared to lambs born from ewes that have lambed for the first time, indicating a strong maternal influence of second parity ewes probably through higher milk production compared to the first time lambers. Lamb survival within two weeks of birth was strongly influenced by birth type, dam parity, and season of birth but not by breed and sex. More than 97 % of single born lambs survived to 15 days of age compared to 91 % for twins (P < 0.001). Likewise more (97 %) lambs born to second parity ewes survived to 15 days after birth as opposed to about 92 % for lambs born from ewes of first parity (P <0.001). The survival rate between birth and weaning (90 days) for Menz lambs (89 %) was significantly (P < 0.001) higher than that for the Horro (76 %). Menz lambs had also a much better post-weaning survival rate from birth to 180, 270 and 365 days of age (81, 71 and 62 %, respectively) compared to Horro (51, 39 and 37 %, respectively). This shows that Horro lambs might have adaptation problems as they are introduced from a different region of the country.
Horro and Menz lambs did not differ significantly in heart girth measurement. However Horro lambs were taller (P < 0.001) at withers at one year of age compared to Menz (61.91 ± 0.62 cm vs 59.89 ± 0.44 cm). The greatest difference observed between the two breeds is in tail length at all stages. Although both breeds are characterised as fat tailed sheep, Horro sheep have longer tail while Menz have a shorter and relatively wider tail.
A strong and significant (P < 0.001) correlation between body weight and the linear body measurements considered in this study was observed at all stages of growth. From what is observed in this study, body weight at one year of age for both breeds could be fairly accurately estimated from heart girth (r = 0.90 for Menz and r = 0.86 for Horro).
At the end of a 123 days fattening period, Horro lambs were significantly heavier (P < 0.05) than Menz lambs (34.7 ± 0.63 kg vs 32.7 ± 0.57 kg). While no significant difference (P > 0.05) was observed in rate of weight gain during the fattening period (45.5 ± 2.90 g for Menz and 47.3 ± 3.81 g for Horro). Horro lambs had a significantly higher (P <0.01) daily dry matter intake compared to the Menz (879.6 ± 12.27 g vs 802.2 ± 9.35 g respectively). However, the dry matter intake of both breeds based on metabolic body weight (kg W0.75), 67.8 ± 1.95 g for Horro lambs and 65.6 ± 1.72 g for Menz, was not significantly different (P > 0.05). Horro lambs had a significantly higher (P < 0.01) proportion of the full Gastro-Intestinal-Tract than Menz lambs (22.6 ± 0.53 % vs 20.1 ± 0.47 %, respectively). The two breeds have also differed significantly in the GIT contents calculated as percent of the fasted slaughter weight compared (15.2 ± 0.52 % for Horro and 13.3 ± 0.46 % for Menz). Nevertheless, despite their higher dry matter intake, the apparent digestibility estimate for Horro was significantly lower (P < 0.01) than that for Menz lambs (51.6 ± 0.01 % vs 54.0 ± 0.01 % respectively).
113Horro and Menz lambs were not significantly different (P > 0.05) in both hot and cold carcass weights (14.2 ± 0.26 kg for Horro and 14.8 ± 0.29 kg for the Menz, and 13.6 ± 0.26 kg for Horro and 14.2 ± 0.29 kg for the Menz, respectively). However, Menz lambs tended to have a better but not significantly different (P > 0.05) dressing % than the Horro (49 % vs 48.0 %). Horro lambs had a higher but not significantly different (P > 0.05) total dissectible lean estimate than Menz (8.91 ± 0.22 kg vs 8.55 ± 0.19 kg respectively).
On the other hand, Menz lambs tended to have slightly more but not significantly different (P > 0.05) dissectible body fat estimate compared to Horro (2.88 ± 0.11 kg vs 2.77 ± 0.12 kg respectively). The two breeds have differed significantly P <0.01) in total carcass bone estimate (3.31 ± 0.08 kg for Horro and 2.99 ± 0.07 kg for Menz) indicating that the Horro has a potential to put more weight than the Menz.
Fat deposition was estimated directly (by dissection) and indirectly (through ether extraction). The two breeds have fairly similar body fat distribution. However, lean from Menz lamb carcasses had significantly higher (P < 0.01) ether extract estimate on dry matter bases compared to that of the Horro (22.4 ± 0.89 % vs 18.1 ± 1.00 % respectively). This is also reflected in the total carcass lean ether extract estimate where the estimate for Menz lamb was significantly higher (P < 0.05) than that of the Horro (505 ± 25.86 g vs 411.00 ± 28.95 g, respectively). This is probably an indication showing that lean from Menz carcasses has more inter- and intramuscular fat than lean from Horro carcasses. Menz lambs also tended to have a better (P < 0.05) lean : bone ratio compared to Horro lambs (2.9 : 1 vs 2.7 :1, respectively). Considering the dressing percentage values, the higher proportion of intramuscular fat as indicated by a higher ether extract estimate of the lean part and a relatively higher lean : bone ratio, Menz lambs seem to be a relatively better meat breed compared to the Horro under the given experimental conditions. However more detailed studies need to be carried out for a conclusive result.
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