enetic analysis of calf survival at different preweaning ages in beef cattle

The aim of this paper is to assess the suitability of including calf survival traits in the breeding objective of beef cattle improvement programs. To do so, we analysed the genetic parameters affecting calf survival during the perinatal period (PS), between the perinatal period and weaning (LM) and at weaning (WS) using Asturiana de los Valles breed field data. Up to 36 125 calf survival records were used in the analysis. Heritabilities estimated for the direct effect ranged from 0.033 to 0.084 for PS, from 0.011 to 0.112 for LM and from 0.039 to 0.142 for WS. Our results suggest that LM is not affected by a maternal genetic component, whereas its effect is slight and similar in magnitude for both PS and WS. In general, the analysed traits are affected by a slight maternal permanent environmental effect ranging from 1 to 2%. PS and WS seem to be consistently determined by the same genes, presenting genetic correlations between the respective direct or maternal genetic effects of 0.95 and 1.0. Genetic correlation between the direct effects affecting PS and LM was 0.745. Current analyses show that WS has a higher genetic variability than would justify the inclusion of calf survival at weaning in the beef cattle breeding objective.  2003 Elsevier B.V. All rights reserved.