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Abstract
The preweaning calf survival (SW) is one of the main economic bottlenecks of beef cattle rearing systems, however there is still few quantitative studies approaching this issue. Being a binary trait, genetic parameters for SW can be estimated considering continuous or categorical data under frequentist and Bayesian methods providing support for the selection and mating of animals in breeding programs. Therefore, the objectives in this study were to obtain and compare the variance component estimates for preweaning calf survival of calves in single-trait analyses and their correlations with a continuous trait in two-trait analyses. An amount of 25 218 data of the categorical trait of calf survival until weaning (SW) and the continuous trait of weaning weight (WW) were collected between the years of 2000 and 2012 in six herds of Nellore cattle. Methods III of Henderson, Maximum Restricted Likelihood (REML), Bayesian Inference and Generalized Linear Mixed Model (GLMM) were tested. Variance components obtained in one-trait analyses were similar to those obtained in two-trait analyses. Estimates of heritability (h2) obtained with different models for SW ranged from 0.0206 to 0.2644. The comparison between different estimation methods in single or two-trait analysis models allows the conclusion that the most appropriate method for SW analysis was the Bayesian estimation under an animal model and assuming linear distribution for phenotypes of SW trait.
Highlights
Preweaning calf mortality is one of the main economic bottlenecks of beef cattle rearing systems (Bourdon & Golden, 2000)
Besides being little studied in zebu breeds, such as the Nellore cattle, there is no definite consensus regarding the best methodology or combinations of methodologies to be adopted in the genetic analysis of preweaning calf survival
Variance components estimated by Generalized Linear Mixed Model (GLMM) were obtained assuming a threshold distribution for the data and using ASREML program (Gilmour et al, 2015) with the link functions Probit and Logit
Summary
Preweaning calf mortality is one of the main economic bottlenecks of beef cattle rearing systems (Bourdon & Golden, 2000). For Nellore cattle, the most important and populous zebu cattle in Brazil, losses of 6% (Corrêa et al, 2000) and 7.99% (Schmidek et al, 2013) until weaning were reported for calves in extensive breeding. The trait called preweaning calf survival represents the mortality of calves at this stage of life (until to the weaning). It has a binomial distribution, assuming the phenotypes 0 or 1 for calves that died before weaning, and 1 or 2 for calves that were alive at weaning. Besides being little studied in zebu breeds, such as the Nellore cattle, there is no definite consensus regarding the best methodology or combinations of methodologies to be adopted in the genetic analysis of preweaning calf survival. The aim in this study was to estimate variance components for categorical survival until weaning trait of Nellore calves by using alternative models in single-trait analyses and their correlations with a continuous trait in two-trait analyses
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