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Genetic and Phenotypic Parameters of Longevity in Australian Dairy Cattle

Livestock Improvement Unit, Victorian Department of Agriculture and Rural Affairs, East Melbourne, Victoria 3002, Australia

ABSTRACT

A new method of evaluating cows for longevity based on survival scores (S_i is presented. Survival is defined as S_i = 1 if the cow survives from i to i + 1 yr after first calving, or S_i = 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 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.

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