Abstract
Abstract. In the present study the growth data of Mehraban sheep were used to estimate direct and maternal additive genetic effects together with direct and maternal permanent environmental effects on body weight from birth to 270 days of age using random regression models. The fixed effects of the model were age of dam, type of birth and contemporary groups. Animal, dam, animal and maternal permanent environmental effects were considered as random effects. The models were fitted to the data using Legendre polynomials for age of lambs. Changes in residual (measurement error) variance with age were modeled by a variance function. Direct heritability estimates for the later ages with the least records tended to be overestimated, particularly heritability beyond 180 days. Maternal heritability estimates increased after birth to a maximum around 120 days of age and decreased thereafter. The results showed that covariance between weights of lambs for a considerable range of ages can be modelled properly using random regression.
Highlights
Lamb and mutton are traditional sources of protein in Iran and the consumption levels are high in comparison with cattle and goats (YAZDI et al, 1997)
The sheep population in Iran is mainly composed of fat-tailed carpet-wool native breeds
The Mehraban breed is one of the common native breeds of Iran adapted to mountainous areas in western parts of the country
Summary
Lamb and mutton are traditional sources of protein in Iran and the consumption levels are high in comparison with cattle and goats (YAZDI et al, 1997). GHAFOURI KESBI et al.: Estimation of direct and maternal effects on body weight in Mehraban sheep The aim of the present investigation was to estimate genetic parameters due to direct and maternal effects for body weight from birth to 270 days of age using RRM.
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