Statistical models for genetic evaluation of some first kidding and lifetime traits of the Egyptian Zaraibi goats

Abstract

The aim of the present study was to define the best fitting model for genetic evaluation of the Egyptian Zaraibi goats using three statistical models. Models differed based on the inclusion or exclusion of maternal additive genetic effects and the direct-maternal genetic covariance (σam). The models used were; Model 1 (without maternal effects); Model 2 (with maternal effects where σam = 0) and Model 3 (as in Model 2, but σam ≠ 0). The evaluated traits were; litter size at birth (LSB, kid), litter size at weaning (LSW, kid), litter weight at birth (LWB, kg), litter weight at weaning (LWW, kg), first lactation milk yield (FLMY, kg), first lactation length (FLL, day), total milk yield in productive life (TMY, kg) and total lactation length in productive life (TLL, day). Data represented some first lactation and longevity traits. A total of 2270 first kidding records produced from 600 does that were sired by 95 bucks. Statistical analyses were done using VCE-6 software. Model selection was built on the value of Akaike information criterion (AIC). Direct heritabilities were higher than maternal heritabilities in all models, and varied between 0.09 to 0.21, 0.05 to 0.22, 0.11 to 0.24 and 0.05 to 0.20 for LSB, LSW, LWB and LWW, respectively. Direct heritability for yield and lifetime traits were low to moderate and varied from 0.16 to 0.18, 0.07 to 0.34, 0.15 to 0.16 and 0.08 to 0.18 for FLMY, FLL, TMY and TLL, respectively. Maternal heritabilities ranged from 0.02 to 0.30 from models 2 and 3. Direct-maternal genetic correlations were low to moderate, negative for most of studied traits and ranged from −0.01 to −0.38. The inclusion of both direct and maternal effects in addition to the covariances between them in statistical models is recommended for the best genetic improvement of Egyptian Zaraibi goats.