Genetic and Phenotypic Parameters of Longevity in Australian Dairy Cattle

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Abstract
A new method of evaluating cows for longevity based on survival scores (Si) is presented. Survival is defined as Si = 1 if the cow survives from i to i + 1 yr after first calving, or Si = 0 if the cow does not. Herd Improvement records on 253,000 AI-bred cows were used to calculate survival scores, and the genetic and phenotypic parameters of the these scores were examined. Survival was constant at .85 to .86 until S4 after which it declined. Average productive life was 5.8 to 6.6 yr, which is consistent with other Australian estimates. Heritability of survival was low (.004 to .088) especially for S1 and S2. Genetic correlations among survival scores was highest in early years (up to S4), and first lactation milk and fat yields were more highly correlated with early than with late survival. Survival scores were also genetically correlated with temperament, particularly for S0 and S1. For routine sire evaluation, survival scores could be used in a multitrait or a repeatability model. However, given the high longevity of Australian cows and the low heritability, improvement in longevity might be more easily achieved by nongenetic means.