Productive Lifespan of Bull Progeny Groups: Failure Time Analysis

Abstract

For genetic parameters herd lives of 587,013 Holstein cows recorded in Dairy Herd Improvement were analyzed by paternal half-sister analysis and Cox regression models. Length of life was duration in days between birth and failure or censoring. Failure was defined in two ways; first was death or sale for beef as determined from codes of condition affecting record, and second was failure defined by the first criterion or disappearance of a cow from a herd while the herd was on test. Censoring occurred when a cow did not fail. Failures were 227,091 by first and 449,325 by second definitions. Heritabilities for hypothetical transformation of uncensored herd life were .13 and .06 for first and second definitions of failure. Herd life seemed to have positive genetic relationships with yields in first lactations and stayability for both definitions of failure. However, herd life by first definition had closer relation with yield. Herd life from second definition had closer relation with stayability. Neither measure of herd life had any genetic relationship with overall measure of type. Herd life from second definition had no clear genetic trend. Herd life from first definition had only a marginal positive trelad.