An alternative definition of stayability was compared to an usual one. The usual definition in this study classifies the cows with at least three calvings at age of 76 months as success, setting them a value 1, and the ones with less than three calvings at this age as failure, setting them a value 0. The alternative definition sets the cows the values 0, 1, 2, or 3, according to the number of calvings: less than three, three, four, or five calves at age of 76 months, respectively. Heritability estimates and EPDs (Expected Progeny Differences) of stayability were obtained using the information of 4,180 bulls with daughters in the database of the genetic breeding program of the Nellore cattle (PMGRN-USP). Both maternal grandsire single trait linear model and bayesian analysis were part of the MTGSAM_threshold (Multiple-Trait Gibbs Sampler for Animal Models) software. The implementation considered a length of Gibbs chain of 225 thousand, a period of burn-in of 25 thousand and a thinning interval at each 1 thousand runs. The correlation between both ranks was calculated by SAS (Statistical Analysis System). The heritability estimates were 0.07 to the usual definition of the trait versus 0.08 to the alternative one. The rank correlation was 87.5%, with considerable change on bull classifications. According to the estimates of sire variance and heritability and variations on EPDs, it can be concluded that the alternative definition of stayability has greater capacity to detect genetic variation under a linear model.
bayesian; beef cattle; linear model; Nelore; stayability
