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Genetic evaluation of calving ease in Parda de Montaña beef breed based on linear and threshold models

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Authors: X. Cortés-Lacruz, R. Revilla, I. Casasús, A. Sanz, J. Ferrer, P. Banzo y D. Villalba
Issue: 113-2 (158-175)
Topic: Animal Production
Keywords: beef cattle, heritability, threshold model, maternal effects

The main objective of this work was to study the genetic and environmental components of calving ease in the Parda de Montaña beef breed. The calving ease score used to record field data was discussed conducting surveys to farmers. The number of calving ease records used in the study was 5,738. The estimation of variance components and genetic evaluation was performed using a bi-trait model (calving ease and birth weight) using four different models, explaining calving ease as normal or a threshold model, and including or not maternal effects. The proportion of unassisted calving was 70.3%, followed by calvings attended without difficulty (24.9%), attended with difficulty (3.1%), caesarean births (0.9%) and finally, by births with veterinary assistance (0.8%). Frequency of difficult calvings and caesareans was two-fold and four-fold higher, respectively, in first-calving cows than in the rest. Cows with first parity before two years also had twice more difficult calvings and caesareans than cows with first parity after two years and a half. The heritability of calving ease trait obtained from the threshold model was higher than that obtained by the normal model, but both models had similar estimated breeding values (Spearman correlation 0.95). The current system of encoding calving ease used in the selection scheme can be simplified and improved.

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