Productive life of Charolais cows was measured with two discrete traits, number of calvings registered either 48 months or 96 months after first calving and with two continuous traits, lengths of productive life with records censored at the same two time endpoints. Productive life of 75 435 cows bred by 2,865 sires was studied in 265 French herds having at least 100 first calving records between 1990 to 2004. Survival analyses consisted in describing the survival traits with a Weibull or a discrete "grouped data" proportional hazard models. Results showed that as long as the discrete nature of number of calvings is accounted for in the hazard model, the discrete and continuous measures of length of productive life at a specific time endpoint were two expressions of the same biological trait with only a slightly larger genetic variability estimate for the discrete trait and an effective heritability estimate about 0.17.

F. Phocas, Vincent Ducrocq

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 03.13, 2006
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