BIRTH WEIGHT AND LITTER BIRTH WEIGHT IN YANKASA SHEEP: ENVIRONMENTAL FACTORS AND HERITABILITY ESTIMATES

Résumé

A study was conducted to examine the influence of five environmental factors on birthweight (BWT) and litter birth weight (LBWT) and to obtain heritability estimates for both traits in Yankasa sheep. Records of 2490 lambs sired by 133 rams and 1225 lambs sired postnatally by 120 rams from 1983-1993 at Shika were  analysed for BWT and LBWT, respectively. The Yankasa flock was semi-intensively l managed in an accelerated lambing programme. Least-squares means were 2.48±0.03 kg and 3.57±0.03 kg for BWT and  LBWT, respectively. All five environmental LBWT in factors considered (parity, sex, type of birth, Yankasa sheep High season and year of birth) were highly significant (P<0.001) for both traits. Lambs from multiparous ewes had higher body weights than  lambs from primiparous ewes. Likewise,  rainy-season-born lambs were heavier than dry-season-born lambs. Ram lambs were consistently heavier than ewe lambs for both traits, their superiority also being reflected in higher LBWT for mixed sexes. Single born lambs. were, superior to single  lambs for LBWT. Heritability estimates by paternal half sib analysis, after appropriately adjusting data for the fixed effects,were 0.410, 0.8 and 0.12±0.07 for BWT and LBWT,  ; respectively. These results indicate that high  genetic response is expected from selection for  BWT, while low response is expected for LBWT.  Adjustment for environmental effects is necessary to enhance the accuracy of selection for superior individuals in terms of gene expression for these traits.