Genetic parameter estimation for pre-weaning growth traits in Jordan Awassi sheep

Aim: The aim of this study was to estimate the heritability, genetic and phenotypic correlations, and the genetic trends for pre-weaning growth traits including the birth weight (BWT), weaning weight (WWT), pre-weaning daily gain (PWDG), and weaning age (WA) in Awassi lambs. Materials and Methods: A total of 5131 Awassi lambs from two Jordanian sheep breeding stations were used. A multitrait animal model and restricted maximum likelihood methods were used to estimate the covariances between the studied traits. Results: The mean +/- standard deviation of BWT, WWT, PWDG, and WA was 4.48 +/- 0.8 kg, 17.13 +/- 0.7 kg, 0.2 +/- 0.07 g, and 65.5 +/- 0.7 days, respectively. Heritability estimates were 0.30 +/- 0.04 for BWT, 0.19 +/- 0.04 for WWT and PWDG, and 0.2 +/- 0.04 for WA. Positive genetic correlations were obtained between BWT and other traits, while negative correlations were obtained between WWT, PWDG, and WA (-0.50 +/- 0.12) and between WWT and WA (-0.67 +/- 0.14). The positive phenotypic correlation was obtained between WA and PWDG (0.63 +/- 0.01). The highest additive genetic variance was obtained for WA (34.58),while the lowest was estimated for PWDG (6.22E-04). The highest phenotypic variance was obtained for WA (175.5), while the lowest value obtained was for BWT (0.54). Maternal additive variance ranged between 0.13 and 0.03. The genetic trends were around zero for all studied traits. Conclusion: Selection should be conducted using animals with high estimated breeding values through controlled breeding.