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7  Summary

The purpose of the experiments was to assess the pre- and post-weaning productive performance of Cameroon and crossbred (C1 and C2) lambs at stall ambient temperature and at alternating ambient temperature in the climate chamber. During post-weaning growth, the effect of different feeding levels on growth was assessed at stall ambient temperature and in the climate chamber, both the growth performance and physiological reaction at high (31°C/50%RH) ambient temperature during the day and low (15° C/70%RH) at night were assessed between the Cameroon lambs and crossbred lambs. In addition to this, the milk yield performance of the Cameroon and C1 ewes was measured and compared using the suckling method.

The crossbred lambs were obtained by crossing between Cameroon sheep and German breeds of sheep (i. e. Texel, Blauköpfiges Fleischschaf, Rauwolliges Pommersches Landschaf, Coburger Fuchsschaf, Braunes Bergschaf, Merino Landschaf, Weißes Ostfriesisches Milchschaf and Braunes Ostfriesisches Milchschaf). The following categories of animals were used in the pre-weaning growth experiment: 67 (9 Cameroon, 31 C1, 27 C2) suckling Cameroon and crossbred male and female lambs in 1994 and 60 (11 Cameroon, 21 C1 and 28 C2) suckling Cameroon and crossbred male and female lambs in 1995. The following categories of animals were used in the post-weaning growth experiments: 30 (10 Cameroon, 10 C1 and 10 C2) weaned male and female lambs in 1995 and 10 (5 Cameroon and 5 C2) weaned male and female lambs reared at 31°C/50%RH vs. 15°C/70%RH in 1996. For the milk yield performance experiment, the following genotypes were used in 1995: 17 (8 Cameroon and 9 C1) ewes.

Numerically, about 46% of the C1 crossbred lambs were produced by crossbreeding between the Cameroon and the Texel; and 47% of the C2 crossbred lambs were produced by breeding the C1 (Cameroon x Weißes Ostfriesisches Milchschaf) with another C1 (Cameroon x Braunes Ostfriesisches Milchschaf).

Parameters used included live body weight, milk yield, feed intake, water intake, rectal temperature, breathing rate and carcass evaluation.

All experiments were conducted at the Animal Research Station of the Faculty of Agriculture and Horticulture of the Humboldt University Berlin at Dahlem, Berlin.

The results of the experiments can be summarised as follows:

7.1 Comparative pre-weaning growth performance of lambs of different genotypes

  1. Recorded birth weight (p 0.001) and estimated Average Daily Gain from birtth to 90days of age (p 0.001) of the C1 and C2 crossbred lambs was significantly higher than that of the Cameroon lambs.
  2. Recorded birth weight of the C1 crossbred lambs was significantly (p 0.001) higher than that of the C2 crossbred lambs although the estimated pre-weaning Average Daily Gain of the latter from birth to 90 days of age was significantly (p 0.05) higher.
  3. Estimated Average Daily Gain remained constant for the Cameroon lambs from 0 - 30, 30 - 60 and 60 - 90 days of age. For the C1 and C2 lambs, ADG showed highest values from 0 - 30 days of age and lower values later.

7.2 Milk yield performance of Cameroon and C1 ewes using the suckling method

  1. The milk yield performance of the C1 ewes was highly significantly (p 0.001) higher than that of the Cameroon ewes.
  2. The milk yield performance of the C1 ewes was highest in early lactation but declined gradually with advance in the stage of lactation. Contrary to this, the performance of the Cameroon fell sharply after the third week of lactation.


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7.3  Comparative post-weaning growth performance of lambs of different genotypes

7.3.1 Influence of different feeding levels on performance

  1. A significant (p 0.05) difference in live body weight of lambs subjected to High-Low and Low-High feeding only occurred during the 12th week in favour of the latter treatment. The end-weight of the C1 and C2 crossbred lambs was significantly (p 0.001) higher than that of the Cameroon lambs. Although the difference between the C1 and C2 crossbred lambs was not significant (p < 0.05), the latter had heavier end-weight than the former.
  2. Average daily gain was significantly higher (p 0.001) for the Low-High feeding treatment than for the High-Low over the whole experimental period. The C1 and C2 crossbred lambs exhibited significantly (p 0.001) higher ADG than the Cameroon lambs over the whole experimental period. The difference between the C1 and C2 crossbred lambs was not significant although the former had higher gain than the latter. During the first six (1 - 6) weeks of the experiment, the C2 achieved higher ADG than the C1 although the difference between them was not significant. However, the C1 achieved significantly (p 0.01) higher ADG than the C2 during the last six (7 - 12) weeks of the experiment. Average daily gain seen on weekly basis showed a completely different pattern of reaction attributable to treatment.
  3. Intake of metabolisable energy over the whole experimental period did not differ significantly between High-Low and Low-High feeding. Intake of energy above maintenance level was, however, significantly higher for the Low-High feeding treatment than for the High-Low one. This is explained by the significant (p 0.001) difference during the High phase of feeding (7 - 12 weeks) of the Low-High feeding treatment. Intake of energy above maintenance level did not differ significantly between the Cameroon, C1 and C2 crossbred lambs. The Cameroon, however, recorded the highest value, followed by the C2 crossbred lambs and lastly the C1 crossbred lambs.
  4. Intake of wheat straw by lambs subjected to High-Low and Low-High feeding was not significantly different over the whole experimental period. For each treatment, significant intake of wheat straw was associated by the Low phase of feeding. The difference between the three genotypes was significant in the order given: The C1 and C2 crossbred lambs consumed significantly more (p 0.001) than the Cameroon lambs due to heavier live weight but the difference between and the C1 and C2 crossbred lambs was not significant although the latter consumed more. Higher relative intake of wheat straw (as % of DM intake) by the C1 and C2 crossbred lambs compared with that of the Cameroon was associated with the High phase of feeding.

7.3.2 Reaction to high ambient temperature during the day and of alternating feeding levels

  1. There was no significant difference in ADG between the Cameroon and C2 crossbred lambs over the whole experimental period even if the latter recorded a higher value. The C2 crossbred lambs, however, recorded significantly (p 0.05) higher ADG than the Cameroon lambs during the second High phase of feeding (9 - 12 weeks). Male lambs also recorded significantly (p 0.05) higher ADG than female ones during the second High phase of feeding (9 - 12 weeks) and over the whole experimental period.
  2. Intake of metabolisable energy (p 0.01) and of concentrated feed (p 0.05) was significantly higher for the C2 crossbred lambs than for the Cameroon lambs because of heavier live weight and significantly (p 0.01) higher for the males than for the females over the whole experimental period. However, intake of energy above of maintenance level was significantly (p 0.01) higher for the Cameroon lambs than for the C2 crossbred lambs during the first High phase of feeding (1 - 4 weeks) as well as over the whole experimental period (p 0.05). Intake of energy above of maintenance level was significantly (p 0.05) higher for the males than for the females during the second High phase of feeding (9 - 12 weeks).
  3. Intake of wheat straw was significantly (p 0.05) higher for the C2 crossbred lambs than for the Cameroon lambs during the first High phase of feeding (1 - 4 weeks).[page 93↓]
  4. High ambient temperature during the day and High-Low-High feeding could not be seen, in physiological terms, to constitute a limiting factor in the rearing of pure Cameroon and C2 crossbred lambs.
  5. Irrespective of genotype, rectal temperature measured at 1200 hrs with 31°C/50%RH ambient temperature was lower than that measured at 2000 hrs with 15°C/70%RH ambient temperature except during 5 - 8 weeks in the case of the C2 crosses. Rectal temperature and breathing rate per minute recorded in the females was always higher than that recorded in the males. Lower rectal temperature recorded in the males than in the females has been associated with significant intake of energy (see above). Breathing rate per minute recorded in the C2 crossbred lambs was for the most part higher than that recorded in the Cameroon. Compared with the first High phase of feeding (1 – 4 weeks), the Low phase of feeding (5 - 8 weeks) followed by the second High phase of feeding (9 - 12 weeks) increased the significant difference in rectal temperature measured at 1200 hrs with 31°C/50%RH ambient temperature - between the Cameroon lambs and the C2 crossbred lambs and between male and female lambs. It also increased the significant difference in rectal temperature measured at 2000 hrs with 15°C/70%RH ambient temperature between the Cameroon lambs and the C2 crossbred lambs and between male and female lambs.
  6. Significant differences in rectal temperature between the Cameroon lambs and the C2 crossbred lambs measured at 1200 hrs with 31°C/50%RH ambient temperature and at 2000 hrs with 15°C/70%RH ambient temperature were compensated for: lower rectal temperature recorded in the Cameroon lambs and higher recorded in the C2 crossbred lambs at 1200 hrs with 31°C/50% than at 2000 hrs with 15°C/70%RH ambient temperature, respectively. However, significant differences in rectal temperature measured at 1200 hrs with 31°C/50%RH ambient temperature and at 2000 hrs with 15°C/70%RH ambient temperature between male and female lambs were not compensated for.
  7. Compared with the first High phase of feeding (1 – 4 weeks), the Low phase of feeding (5 - 8 weeks) increased the significant difference in breathing rate per minute measured at 1200 hrs with 31°C/50%RH ambient temperature, between the Cameroon lambs and the C2 crossbred lambs. Again compared with the first High phase of feeding (1 – 4 weeks), both the Low phase of feeding (5 - 8 weeks) and the second High phase of feeding (9 - 12 weeks) increased the significant difference in breathing rate per minute between males and females.

7.4 Carcass evaluation

7.4.1 Influence of different feeding levels on performance

  1. Significant increase in ADG as a result of Low-High feeding was due to significant increase in weight of the digestive organs. Low-High feeding also resulted in slight but not significant increase in the weight of the carcass and muscle, fat (except middle) and bones (except for foreleg, middle and neck) of the seven selected valuable parts.
  2. The C2 crossbred lambs produced a much heavier Right Half than either the C1 crossbred lambs or the Cameroon. In terms of the relative weight of muscle to carcass part, the C1 and C2 crosses achieved significantly higher values for most parts (foreleg, back, and hindleg) than did the Cameroon. For breast and neck, relative weight of the C2 was significantly higher than that of both the Cameroon and C1 lambs.
  3. The weight of the coat of the crossbred lambs was significantly (p 0.001) heavier than that of the Cameroon lambs. The weight of the coat was not significantly different between the C1 and the C2 but that of the former was slightly heavier.
  4. The effect of treatment on the relative weight of total fat, kidney and mesenteric fat was not significant. However, the effect of genotype (p 0.05) and sex (p 0.01) on the same was significant. The Cameroon lambs had significantly higher values than both the C1 and C2 crossbred lambs. The difference between the C1 and C2 crossbred lambs failed to be significant at p 0.05 although the latter had higher values than the former. Female lambs had significantly higher values than male lambs.


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7.4.2  Reaction to high ambient temperature during the day and of alternating feeding levels

  1. The C2 recorded significantly higher carcass values than the Cameroon lambs for almost all traits. Relative weight of muscle to carcass part of the C2 was highly significantly (p 0.001) for hindleg and thinning. Thus compared to the influence of different feeding levels under stall ambient temperature conditions mentioned above, high ambient temperature affected the C2 lambs by limiting the growth of muscle of most valuable carcass parts (except the in the case of hindleg and neck) when compared with the Cameroon lambs in both cases.
  2. At an ambient temperature of 31°C/50%RH during the day and 15°C/70%RH at night, the Cameroon lambs recorded a significantly higher value for relative weight of total (p 0.01), kidney (p 0.001) and mesenteric (p 0.001) fat than the C2 crossbred lambs. A reverse trend in deposition of relative weight of mesenteric fat was observed compared to the trend in the previous experiment such that the males gained more than the females and although the difference was not significant in relative terms, it was significant (p 0.05) in absolute terms. The Cameroon and the males form the category of animals that recorded significantly lower rectal temperature and breathing rate during the day. Lower rectal temperature and breathing rate was therefore associated with increased deposition of mesenteric fat and this fact may constitute a mechanism of thermoregulation following long periods of exposure to high ambient temperature.


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