Phenotypic and genetic relationships between lamb and ewe traits for the Sabi sheep of Zimbabwe

Abstract

Genetic and phenotypic correlations were estimated between lamb and ewe traits in a flock of Sabi sheep reared at the Matopos Research Station. Direct additive estimates of heritability were: 0.28 ? 0.04; 0.17 ? 0.00; 0.25 ? 0.01; 0.39 ? 0.01; 0.59 ? 0.01; 0.50 ? 0.01; 0.68 ? .03; 0.12 ? 0.003; 0.25 ? 0.01; 0.11 ? 0.00; 0.12 ? 0.00; for birth weight, weaning weight (120 days), 12 month weight, 18 month weight, ewe mating weight, post partum weight, ewe weight at weaning of lamb, total weight of lamb weaned, slaughter weight, hot and cold carcass weights respectively. Genetic correlations between birth weight and other weights to 18 months were high (0.75-0.85), whilst the relationship between weaning, 12 month and 18 month weight was close to unity. The genetic correlation between birth weight and ewe weights (mating, post-partum and dam weight at weaning of lamb) were moderate viz. 0.51 ? 0.08, 0.40 ? 0.09, 0.49 ? 0.07 respectively and were close to unity at 18 months of age viz. 0.96 ? 0.02, 0.92 ? 0.03, and 0.84 ? 0.03 respectively. Total weight of lamb weaned was moderately correlated to birth weight (rg = 0.46 ? 0.15) but tended to be highly correlated with 18 month weight (0.92 ? 0.10) and ewe weights (0.75 ? 0.09-0.91 ? 0.07). The genetic correlation between birth weight and slaughter and carcass weight was moderate and was high at 18 months. The heritability estimates from a univariate logit transformed analysis for fertility, prolificacy and lamb survival were 0.08 ? 0.04, 0.22 ? 0.03, and 0.01 ? 0.02 respectively. The genetic correlation between fertility and lamb weight and ewe weights was low (-0.08 ? 0.004, to 0.06 ? 0.02) and some estimates had large standard errors. The genetic correlation between prolificacy and birth weight was close to zero. The genetic correlations between prolificacy and weaning weight, 12 month weight, 18 month weight, ewe mating, post-partum and ewe weight at weaning were 0.07 ? 0.02; 0.12 ? 0.00; 0.07 ? 0.02; 0.22 ? 0.00; 0.13 ? 0.00; 0.24 ? 0.00 respectively, and that between fertility and prolificacy was negative (-0.17 ? 0.07). Genetic correlations between lamb survival and birth weight, weaning weight, 12 month weight, 18 month weight and total weight of lamb weaned were 0.18 ? 0.00, 0.26 ? 0.00, 0.15 ? 0.00, 0.15 ? 0.00, 0.13 ? 0.00 respectively. Selection for birth weight and total weight of lamb weaned have possible uses in a selection index for the Sabi flock. South African Journal of Animal Science, Vol 31, Issue 3, Oct – Dec (2001) pp.215-222

Key Words

Fat-tailed hair sheep, Production, Reproductive traits, Lamb survival, Correlations