Animal Science Abstract
Factors influencing length of productive life and replacement rates in the Bruna dels Pirineus beef breed
J. Tarrés1, P. Puig2, V. Ducrocq3 and J. Piedrafita1,A
ACorresponding author. E-mail: jesus.piedrafita@uab.es
1Departament de Ciència Animal i dels Aliments, Grup de Recerca en Remugants,2Departament de Matemàtiques, Servei d'Estadística,
3Station de Génétique Quantitative et Appliquée, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas, France
Abstract
An analysis of the length of productive life in the Bruna dels Pirineus beef breed was performed with a non-parametric approach giving an average value of 9 years of productive life, and a corresponding replacement rate of 11%. Using a proportional hazards model stratified by herd, the influence of calf birth weight and weight gain until weaning, calving difficulty, calving interval and age at first calving on length of productive life were studied. Two models were explored : the first one included time-dependent variables taking the current value of the covariate at each calving date, while the second one also comprised time-dependent interactions between the value of the covariate of the current calving and its mean value during the last (up to) three previous calvings. Results from the first model showed that the risk of culling increases with very high ages at first calving, increasing calving difficulties, very large calf birth weights, very small weight gains until weaning and very long calving intervals. Furthermore, results from the second model showed that these increases also depend upon a sequence of values for the same covariate in previous calvings. Finally, these higher risks of culling implied lower survival functions that increased replacement rates but only slightly decreased average performances.
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