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1 Dairy Production Department, Teagasc, Moorepark Production Research Centre, Fermoy, Co. Cork, Ireland
2 Livestock Improvement, and
3 Animal Evaluation Unit, Private Bag 3016, Hamilton, New Zealand
Corresponding author: D. P. Berry; e-mail: dberry{at}moorepark.teagasc.ie.
A proportional hazards model was used to investigate the phenotypic effect of traits other than production (TOP) on true and functional longevity across purebred and crossbred Holstein-Friesian and Jersey dairy cattle in registered and commercial herds in New Zealand. The hazard function was described as the product of a baseline hazard function and the time-independent effects of age at first calving, heterosis, proportion of breed, period of last calving relative to herdmates, and TOP; a time-dependent effect of herd-year was also included. The influence of TOP on functional longevity was assessed by adjusting true longevity for the time-independent effects of production values as well as the time-dependent effects of deviation of milk, fat, and protein yield within contemporary group. All analyses were stratified by breed, and separate analyses were carried out for registered or commercial herds. All TOP were significantly related to true and functional longevity. Obvious differences existed in the relative influence of individual TOP on longevity in registered or commercial herds. Of the individual TOP describing the physical characteristics of the cow, the udder-related TOP exhibited the largest influence on functional longevity. Farmer opinion explained the largest proportion of variation in true and functional longevity among cows. In commercial herds, the risk of culling in cows with very low farmer opinion was 1.5 to 2.0 times that in cows with average or high farmer opinion.
Key Words: survival analysis • longevity • New Zealand • dairy
Abbreviation key: AIC = Akaike’s information criterion, TOP = traits other than production
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