737
Estimation of genetic parameters for age at last calving as a measure of Cow Survival in a Population of Nellore Beef cattle in Brazil
Longevity was measured by the variable age of cow at last calving. The date of the last calving occurred in the farm was used as a reference moment. If the difference between the age of cow at last calving and this moment was greater than a predetermined criterion, the cow was considered to disposal. Otherwise, it could remain in the herd. A Weibull proportional hazards model was used to estimate heritabilities for age of cow at last calving considering three values of the criterion: 16, 26 and 36 months. The heritability estimates obtained for age of cow at last calving considering criteria values of 16, 26 and 36 months, respectively: 0.1020, 0.1002 and 0.0871. The phenotypic variance was explained mostly by the non-additive genetic and environmental effects. Selection response for this trait would be low.
Keywords: Heritability, Survival analysis, Weibull model
