Variances of direct and maternal genetic effects for milk yield and age at first calving in a herd of Friesian cattle in Egypt

Abstract. A total of 2095 lactation records of Holstein Friesian cattle kept at Dalla Farm in Egypt during the period from 1988 to 1992 were used in this study. Those data were used to estimate variances from direct and maternal genetic effects. The data was analyzed by using Multiple Traits Derivative Free Restricted Maximum Likelihood (MTDFREML) according to BOLDMAN et al. (1995) using repeatability Animal Model. Two models were used: Model 1 includes month of calving, year of calving, parity as fixed effects, days open and days dry as covariates and direct genetic, maternal genetic, covariance between direct and maternal genetic, permanent environmental and residual as random effects; Model 2 is similar to Model 1, but excluding additive maternal and covariance between additive direct and maternal effects.

Estimates of heritability for 305 day milk yield (305 dMY) were 0.22 and 0.23, for Model 1 and Model 2, respectively. Heritability estimates for age at first calving (AFC) were 0.77 and 0.82 for Model 1 and model 2, respectively. The removal of additive maternal genetic effects and covariance between direct and maternal genetic effects from the model increased estimates for heritability of additive genetic effects by 0.01 and 0.05 for 305 dMY and AFC, respectively. Then, the additive maternal genetic effect and covariance between direct and maternal genetic effects do not seem to make important contributions to the phenotypic variance for milk yield and age at first calving, and these effects are probably not important for genetic evaluations.