Productive Lifespan of Bull Progeny Groups: Failure Time Analysis

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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 2 ways: 1st was death or sale for beef as determined from codes of condition affecting record, and 2nd 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 1st and 449,325 by 2nd definitions. Heritabilities for hypothetical transformation of uncensored herd life were 0.13 and 0.06 for 1st and 2nd definitions of failure. Herd life seemed to have positive genetic relationships with yields in 1st lactations and stability for both definitions of failure. Herd life by first definition had closer relation with yield. Herd life from 2nd definition had close relation with stability. Neither measure of herd life had any genetic relation with overall measure of type. Herd type from 2nd definition had no clear genetic trend. Herd life from 1st definition had only a marginal positive trend.