02398naa a2200205 a 450000100080000000500110000800800410001910000160006024501390007626000090021552017950022465000170201965000140203665300230205065300210207370000180209470000170211270000160212977300470214520642182023-01-30       2016    bl uuuu     u00u1 u    #d1 aKERN, E. L.  aSurvival analysis of productive life in Brazilian holstein using a piecewise Weibull proportional hazard model.h[electronic resource]  c2016  aAbstract The objectives of this study were to assess the most important factors that influence productive life (PL) of Brazilian Holstein cows and to estimate genetic parameters for PL using a piecewise Weibull proportional hazard model. Records of PL from first calving to last recording (culling) of 132,922 cows coming from 945 herds were used. They had to have their first calving occurring between 1989 and 2013 and they were daughters of 6,804 sires. The model included the time-dependent effects of region within year, class of milk production within herd-year, class of milk production within lactation number, class of fat and protein contents within herd and (variation in) herd size as well as the time-independent fixed effect of age at first calving, the random effects of herd-year, sire and maternal grand sire. All fixed effects had a significant effect on PL (Po0.001). The relative risk (RR) for within herd class of milk yield varied from 3.16 for the worst 20% class to 0.41 for the best 20% class. RR also increased as protein and fat decreased, but to a lesser extent compared to milk yield. Significant effects on PL were found for regionyear, with large yearly changes in some cases. RR increased with age at first calving and with herd size but lower risks were observed when herd size was increasing or decreasing, compared to stable herds. The Weibull shape parameters (and therefore RR) increased with lactation number and with stage of lactation. The sire genetic variance estimate was 0.03070.002 which corresponds to an equivalent heritability estimate of 6.1% accounting for censoring. A positive genetic trend of PL was observed. These results may contribute to the development of a routine genetic evaluation necessary to improve PL of Brazilian Holsteins.  adairy cattle  alongevity  aEnvironment effect  aGenetic analysis1 aCOBUCI, J. A.1 aCOSTA, C. N.1 aDUCROCQ, V.  tLivestock Sciencegv. 185, p. 89-96, 2016.