Estimation of covariance functions for growth trait from birth to 180 days of age in Iranian Baluchi sheep

Weights of Iranian Baluchi sheep, from birth to 180 d of age, recorded every month, were analyzed using Random Regression Models. Independent variables were Legendre polynomials of age at recording. Up to four sets of random regression coefficients were fitted for animals' direct and maternal additive genetic and permanent environmental effects. Changes in measurements of error variances by age were modeled through a variance function. Orders of polynomial fit from three to five were considered and resulted in up to 36 parameters to be estimated. Direct heritability estimates increased after birth and tended to be the highest at ages at which maternal effect estimations tended to be the lowest. Maternal heritability estimations decreased fast after birth to about 30 of age and decreased slowly after that. Estimations of direct and maternal additive genetic correlation between weights of birth with other ages were moderate and between other ages were high.