Genetic parameter estimates of growth traits in Kurdi sheep, using random regression model

Genetic parameters of body weight using random regression model were estimated using 22881 live body weight test day records collected on 6599 lambs during 1990 to 2007 at the rearing and Kurdi sheep breeding station in Shirvan. The model was included fixed effects (year of birth، sex of lamb، birth type of lamb and age of dam) and random effects direct additive genetic، maternal additive genetic، permanent environmental and residual. Random regression models were fitted with order 2 to 6 for direct additive genetic، maternal additive genetic and permanent environmental effects. Results indicated that the 6th order was more appropriate than others. The values of direct heritability with this model for lamb body weight at birth، 2، 3، 4، 5، 6، 7، 8، 9، 10، 11 and 12 months of age were estimated as 0. 06، 0. 27، 0. 31، 0. 35، 0. 35، 0. 33، 0. 30، 0. 28، 0. 27، 0. 28، 0. 29 and 0. 28 respectively. The values of maternal heritability with this model were estimated as 0. 24، 0. 03، 0. 06، 0. 09، 0. 10، 0. 12، 0. 13، 0. 12، 0. 11، 0. 10، 0. 10 and 0. 08 respectively. The proportion of permanent environmental variance to phenotypic variance was increased from 0. 05 for birth weight to 0. 69 for body weight at 2 months of age، up to 5 months of age reduced and then increased with increasing age of lamb. Direct and maternal genetic correlations between body weights at different ages were positive and ranged from 0. 16 to 0. 99 and 0. 25 to 1. 00، respectively، at closer ages were higher and decreased with increasing intervals age. In general the results obtained in this study suggested that lamb body weight were influenced by different factors (direct and maternal additive genetic and permanent environment)، and due to various estimated heritability for lamb body weight from birth to 12 months of age، it could be concluded that some different genes might be affect lamb body weight at birth to 12 months of age.