THRESHOLD SIRE MODELS FOR ESTIMATING GENETIC PARAMETERS FOR STAYABILITY IN BEEF COWS

Stayability is the ability of a beef cow to remain in production to a specified age. In this study, the interest was in determining the genetic relationship between stayability to an early age with stayability to a later age. A nested threshold sire model for stayability was used here to estimate the genetic relationship between stayability to different ages. Genetic correlations were estimated among six different stayability traits using records from 1,868 Hereford cows. The model included period and year of birth as fixed factors and sire as a random factor. The numerator relationship matrix accounted for all known relationships among sires. Penalized quasilikelihood estimates were obtained using a probit link function. Estimates of heritability on the original scale were small and ranged from 0.09 to 0.17. Estimates of genetic correlations were low to moderate and variable in sign. Results indicate that selection for stayability to an early age would have a limited impact on stayability to later ages