Genetic parameters and factors influencing survival to twenty-four hours after birth in Danish meat sheep breeds
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In this study, influential factors and (co) variance components for survival to 24 h after birth were determined and estimated for Texel, Shropshire, and Oxford Down, the most common sheep breeds in Denmark. Data from 1992 to 2006 containing 138,813 survival records were extracted from the sheep recording database at the Danish Agricultural Advisory Service. Estimation of (co) variance components was carried out using univariate animal models, applying logistic link functions. The logistic functions were also used for estimation of fixed effects. Both direct and maternal additive genetic effects, as well as common litter effects, were included in the models. The mean survival to 24 h after birth was 92.5, 91.7, and 88.5% for Texel, Shropshire, and Oxford Down, respectively. There was a curvilinear relationship between survival to 24 h after birth and birth weight, with survival less for light and heavy lambs. Male lambs, as well as lambs from ewes in the first parity or with difficult lambing, had the least survival to 24 h after birth. Survival to 24 h after birth was greater in twin-born Texel and Shropshire lambs compared with singletons and vice versa in Oxford Down. Estimates of direct heritability were in the range from 0.05 to 0.07. Maternal heritability estimates were slightly greater (0.06 and 0.07) than direct heritabilities in Texel and Shropshire and less (0.04) in Oxford Down. The estimated genetic correlations between direct and maternal effects for survival to 24 h after birth were negative, which will make breeding for this trait more difficult. However, on the basis of estimated genetic parameters, it can be concluded that it is possible to improve survival to 24 h after birth in meat sheep breeds by accounting for both direct and maternal genetic effects in breeding programs.