Variance components and estimates of genetic parameters for early growth traits in Horro sheep

Abstract

Variance components and genetic parameters were estimated for growth traits: birth weight (BWT), weaning weight (WWT), six-month weight (6MWT) and yearling weight (YWT) in indigenous Ethiopian Horro lambs using the Average Information REML (AIREML). Four different models: Sire model (Model 1), Direct animal model (Model 2), Direct and Maternal animal model (Model 3) and Direct-Maternal animal model including the covariance between direct and maternal effect (Model 4) were used. Bivariate analysis by Model 2 was used to estimate genetic correlation between traits. Estimates of direct heritability obtained from models 1 to 4, respectively, were for BWT 0.25, 0.27, 0.18 and 0.32, for WWT 0.16, 0.26, 0.1, and 0.14, for 6MWT 0.18, 0.26, and 0.16 and for YWT 0.30, 0.28, 0.23 and 0.31. Maternal heritability estimates of 0.12 and 0.23 for BWT; 0.19 and 0.24 for WWT; 0.09 and 0.09 for 6MWT and 0.08 and 0.14 for YWT were obtained from Models 3 and 4, respectively. The correlation between direct and maternal additive genetic effects for BWT, WWT, 6MWT and YWT was -0.64, -0.42, 0.002 and -0.46, respectively. On the other hand, the genetic correlation between BWT and the rest of the growth traits (BWT, WWT, 6MWT, and YWT) were 0.45, 0.33 and 0.31, respectively while correlations between WWT and 6MWT, WWT and YWT and 6MWT and YWT were 0.98, 0.84 and 0.87, respectively. The medium to high direct and maternal heritability estimates obtained for BWT and YWT indicate that in Horro sheep faster genetic improvement through selection is possible for these traits and it should consider both h² estimates. However, since the direct-maternal genetic covariances were found to be negative, caution should be made in making selection decisions. The high genetic correlation among early growth traits imply that genetic improvement in any one of the traits could be made through indirect selection for correlated traits.