TAILIEUCHUNG - Báo cáo sinh học: " Survival analysis of longevity in dairy cattle on a lactation basis"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học thế giới đề tài: Survival analysis of longevity in dairy cattle on a lactation basis | 305 Genet Sei. Evol. 35 2003 305-318 INRA EDP Sciences 2003 DOI gse 2003010 Original article Survival anaÍYSÌs of longevity in dairY cattle on a lactation basis Anki Roxstroma Vincent Ducrocqb Erling Strandberga a Department of Animal Breeding and Genetics PO Box 7023 Swedish University of Agricultural Sciences 750 07 Uppsala Sweden b Station de génétique quantitative et appliquée Institut national de la recherche agronomique 78352 Jouy-en-Josas Cedex France Received 4 July 2001 accepted 5 November 2002 Abstract - An analysis of longevity in dairy cattle on a lactation basis is proposed. The approach allowed each lactation to have its own baseline hazard function which gives a better description of the hazard than traditional analyses of the whole length of life. As a consequence the overall fit of the model to the data was improved and fewer time-dependent variables were needed. Longevity on a lactation basis was defined from one calving to the next instead of from the first calving to culling. However no new information was added and it was still the overall risk of being culled that was modelled. It is shown that no cow effect is needed in the lactation basis model because a censored record is not complete a cow can appear as uncensored only once and a cow cannot be censored after having been culled. Different subdivisions of the stage of lactation effect were tested and the first ten days of lactation were shown to correspond to an increased risk of being culled. There were no major differences in sire variance between the longevity analysed on a lactation basis and longevity based on the entire length of life. dairy cows culling frailty models failure time analysis heritability 1. introduction In many of the current genetic evaluation models for longevity the length of productive life in dairy cattle that are based on survival analysis a lactation by stage of lactation lactsta effect is included as the time-dependent covariate in France Germany the .

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