Estimates of genetic parameters for direct and maternal effects on birth weight of local sheep in United Arab Emirates

Genetic parameters for birth weight were estimated for two sets of purebred and crossbred lambs in United Arab Emirates, using animal model methods. Data were analyzed by restricted maximum likelihood (REML). Five different animal models were fitted. Model 1 considered the animal as the only random effect. Models 2 and 3 included in addition to the additive direct effect of the animal, the additive maternal and the permanent maternal environmental effects, respectively. Model 4 fitted both the additive maternal and permanent environmental effects. Model 5 was the same as model 4, except that a covariance between the direct and the maternal additive effects was included. Estimates of direct heritability were substantially higher when maternal effects were ignored. Introducing the additive maternal effect to model 2 reduced the estimate of additive heritability by 28 and 14% of δp² for the purebred and crossbred lambs, respectively. Estimates of additive direct and additive maternal heritabilities with model 4 were 0.10 and 0.33, and 0.45 and 0.10 for purebred and crossbred lambs, respectively. The correlation between direct and maternal genetic effects for the combined (purebred + crossbred lambs) data set was large and negative. These results indicate that in addition to additive direct effect, additive maternal effect for birth weight was important.