GENETIC AND ENVIRONMENTAL FACTORS INFLUENCING PRE-WEANING MORTALITY OF NIGERIAN SHEEP AND THEIR CROSSES
*Iyiola-Tunji1, A.O., Akpa2, G.N., Nwagu3, B.I., Adeyinka3, I.A., Osuhor3, C.U.,
Ojo2, O.A. and Lawal4, T.T.
1National Agricultural Extension and Research Liaison Services, Ahmadu Bello University, Zaria.
2Department of Animal Science, Ahmadu Bello University, Zaria.
3National Animal Production Research Institute, Ahmadu Bello University, Zaria.
4Animal Physiology Laboratory, Department of Animal Science, University of lbadan, lbadan.
*Corresponding author: tunjiyiola@yahoo.com; tunjiyiola@naerls.gov.ng
Abstract
Several factors could be responsible for pronounced mortality rate in sheep production. This study aimed at establishing the possible effect of genotype of lambs and some environmental factors on pre-weaning mortality rate of Nigerian sheep breeds and their crosses. The sheep breeds used were Balami, Ouda and Yankasa which were subjected to diallel crossing. The pure breed lambs were 51 Yankasa (YK X YK), 12 Uda (UD X UD) and 5 Balami (BAL X BAL) while the crosses were 8 Yankasa X Uda (YK X UD), 6 Yankasa X Balami (YK X BAL), 14 Uda X Yankasa, 4 Uda X Balami (UD X BAL), 10 Balami X Yankasa (BAL X YK) and 4 Balami X Uda. A total of 114 lambs were used. Mortality was recorded as at when it occurred. Weaning of lambs was done at 90 days after birth. Effect of genotype and environmental factors on birth weight of lambs was analyzed through analysis of variance and t-test of General Linear Model procedure of SAS. Chi-square procedure was used to test the occurrence of mortality in relation to the factors considered. Correlation procedure of SAS was also used to obtain correlated relationships among birth weight of lambs, type of birth and mortality status in the study. Three crosses (BL X UD, UD X BL, YK X BL) and pure Balami (BL X BL) recorded the biggest birth weight while pure Yankasa (YK X YK) had the smallest weight. Effect of genotype of lambs on mortality status was not significant (P>0.05). The correlated relationship between birth weight and mortality status was positive, moderate and significant (0.30; P<0.05). Correlation coefficient between birth weight and type of birth was however, negative, low and significant (-0.25; P<0.05). Type of birth affected mortality status of sheep (P<0.05). About 70% of lambs born as single survived up to weaning while only 40% of twin-born lambs survived to weaning. Sex and season of birth had no significant effect on mortality status of sheep. Mortality of lambs is not as a result of its genotype. Management practices that will encourage high survival rate of twin-born lambs should be put in place. Genetic resources of between and within breed of Nigerian sheep should be exploited for improved lamb crop to weaning and beyond.
