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* Facultad de Ciencias Agrarias, Universidad Nacional del Litoral, P. Kreder 2805, Esperanza 3080, Argentina
Universidade de Passo Fundo, Faculdade de Agronomia e Medicina Vetorinaria, Barrio São Jose, Brazil
Department of Animal Science, McGill University, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada
Corresponding author: R. I. Cue; e-mail: Roger.Cue{at}McGill.ca.
Survival analysis was used to study the effects of composite and descriptive linear type traits on functional herd life of Quebec Holsteins. Functional herd life was defined as the length of life from first calving to death, culling, or censoring, and was adjusted for 305-d milk production. The dataset contained information from 331,105 cows from Quebec province calving for the first time between 1981 and 1995; 58% of the records had type information. Weibull models were fitted to analyze the data. The hazard function was described as the product of a baseline hazard function and the time-independent effects of age at first calving and type, and the time-dependent effects of year of calving, stage of lactation x lactation number, annual change in herd size, 305-d milk production, and herd-year (random). Analyses were done one at a time for each type trait. The strongest relationships between survival and composite type traits were found for final score, mammary system, and feet and legs. Among the linear type traits, the highest impact on functional herd life was found for traits related to the udder.
Key Words: functional herd life • Holstein • survival analysis • type trait
Abbreviation key: FHL = functional herd life, LPL = length of productive life, RCR = relative culling rate, PATLQ = Programme d’Analyse des Troupeaux Laitiers du Quebec
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