|Awgichew, Kassahun: Comparative performance evaluation of Horro and Menz sheep of Ethiopia under grazing and intensive feeding conditions |
Chapter 5. Conclusion and recommendations of this study
The area around Debre Birhan, where the present study has been undertaken, is known to have a long dry season and a short but intensive rainy season with a small and occasionally erratic wet period in between. The long dry season is characterised by shortage of adequate pasture in terms of both quantity and quality. This in turn affects the performance of livestock reared resulting in body weight losses unless the animals are supplemented if that is affordable.
On the other hand, although the provision of pasture during the wet season is much better than during the dry season, the grazing area will be mostly limited to high grounds due to water logging in the bottomland. This will lead to a high concentration of animals in a limited grazing area resulting in high parasite and disease challenges. In such circumstances, animals adapted to the area are expected to perform better than those which are brought from a different environment.
If, however, different breeds are studied under station management conditions where the effects of external environment could be minimised, it is assumed that differences in performance could be due to the inherent breed differences in the variables tested.
With such assumptions in mind and the results obtained in the present study, the following conclusions could be drawn:
- Horro lambs were heavier at birth and at 30 days of age compared to the Menz (2.4 kg and 5.2 kg for Horro and 2.1 kg and 4.7 kg for Menz, respectively). Sex, birth type, and dam parity have also influenced lamb birth weight. Lambs born at the end of the rainy season tended to be heavier at birth compared to those born at the beginning of the rainy season. This could be due to the provision of qualitatively better forage for the ewes during the wet season which covers the later part of the gestation period.
- Pre-weaning and post-weaning growth performances of both Horro and Menz lambs are in line with what is reported in the literature for tropical breeds. Both breeds had relatively similar rate of pre-weaning weight gain (birth to 90 days of age), 69.4 and 68.1 g for all groups and 70.9 and 67 g for male lambs, respectively). However, to draw a credible conclusion regarding the growth performance of Horro and Menz sheep with the objective of comparative breed evaluation, further studies will have to be carried out in Western highland region of Ethiopia, where the Horro sheep originates and around Debre Birhan which is near to the origin of the Menz sheep. This will allow to see whether there is a significant genetic environment interaction effect influencing growth and rate of weight gain performances of both breeds.
- Survival of lambs within two weeks of birth observed in this study is higher than those reported by others for the same period (96 % for Menz and 94 % for Horro. This is probably a reflection of improved management practices. More Menz lambs (89 %) have survived to weaning (90 days of age) compared to Horro (76 %). There was a drastic decrease in Horro lamb survival after weaning while that of Menz lambs was relatively high. This is probably due to a high disease challenge indicating that Menz lambs, which are relatively adapted to the area, have tolerated the challenge better than the Horro. Lambs born in the wet season tended to have a higher survival rate probably due to a better pasture availability than those born in the dry season. Further investigation is needed to find out whether there exists a possible genotype x environment interaction effect on survival rate of lambs of the two breeds.
- Linear body measurements are significantly and positively correlated to body weight in both breeds. It is observed that body weight could be fairly accurately estimated from heart girth ( r = 0.90 for Menz and r = 0.86 for Horro) and from other linear body measurements for both breeds.
- Male Horro and Menz lambs born in the first dry season of the study period had significantly different final weights and slaughter weights after a four month fattening period where Horro lambs were heavier (P <0.05) than the Menz. Horro lambs also had a higher (P <0.01) daily dry matter intake, larger and heavier gastrointestinal tract, and a higher proportion of GIT content. On the other hand Menz lambs had a lower daily faecal dry matter output and higher digestibility estimate compared to the Horro. The two breeds did not differ significantly in empty body weight (23.0 kg for the Menz and 24.0 kg for the Horro). The fact that Horro lambs had a higher daily dry matter intake compared to the Menz (880 g vs 800 g, respectively) and the higher daily faecal dry matter output (Table 29) indicates that Horro lambs have a low dry matter retention time in the rumen than Menz lambs. This seems to indicate that the Menz is probably more efficient in converting feed to meat because despite their higher dry matter intake, Horro lambs did not differ significantly from the Menz in average daily weight gain during the fattening period. It is necessary to do a study on solid and probably liquid out flow rate to estimate the minimum retention time of dry matter and liquid in the digestive system of both breeds to get conclusive results.
- Horro and Menz lambs did not differ significantly (P >0.05) in all major carcass and non-carcass components. However, Horro lambs had a heavier (P <0.01) total bone estimate than Menz lambs. The two breeds did not differ significantly (P >0.05) in separable carcass composition of the left dissected side. However, carcasses from Menz lambs had a better (P <0.05) lean : bone ratio (2.9 : 1) than that of the Horro (2.7 : 1). Nevertheless, further studies under varying management and environmental conditions should be carried out to see if Menz and Horro sheep do differ in the economically important carcass traits.
- In general there was no marked difference between Menz and Horro lambs regarding fat depot characteristics observed in this study based on the ether extract estimate except the EE estimate for lean (22.4 ± 0.89 for Menz and 18.1 ± 1.00 for Horro). The largest proportion of fat depot in both breeds was the sum of subcutaneous fat and inter-muscular fat followed by tail/rump fat. However there were no significant (P >0.05) breed differences. The high (P <0.01) ether extract estimate of lean component of carcass on dry matter bases indicates that the lean part of Menz lamb carcasses have possibly more inter- and intramuscular fat compared to carcasses of Horro lambs after the 123 days of fattening period. The combined tail and rump fat weight could be fairly accurately estimated for both breeds from live tail volume measurements (r = 0.78 for Horro and r = 0.66 for Menz). However due to the smallness of the sample size care should be taken in the interpretation of the present result as what observed in this study is not a strong indicator. To reach a definitive conclusion, further studies in this line should be undertaken, particularly to see if tail dimension measurements (length, volume, etc.) could be related to fat deposition characteristics of the breeds. Furthermore, detailed studies should be undertaken to identify whether the two breeds are significantly different in their fat deposition characteristics and mobilisation of body reserves.
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