Assessment of the Impact of Somatic Cell Count on Functional Longevity in Holstein and Jersey Cattle Using Survival Analysis Methodology

摘要: Survival analysis in a Weibull proportional hazards model was used to evaluate the impact of somatic cell count (SCC) on involuntary culling rate US Holstein and Jersey cows with first calvings from 1990 2000. The full data set, consisting records 978,043 250,835 cows, divided into subsets (5 for Holsteins 3 Jerseys) based herd average lactation SCC values. Functional longevity (also known as life or length productive life) defined days calving until censoring, after correcting milk production. Our included time-dependent effects herd-year-season, parity by stage interaction, within-herd-year quintile ranking mature equivalent production, (rounded nearest 50,000 cells/mL), well time-independent effect age at calving. Parameters distribution, variance components herd-year-season effects, were estimated within each group herds. Mean failure censoring times decreased increased, nonlinear relationship observed between all groups. risk > 700,000 cells/mL 3.4, 2.7, 2.3 greater, respectively, than that 200,000 250,000 herds low, medium, high SCC. Likewise, 4.0, 2.9, 2.2 These trends may reflect more stringent few mastitis problems. In addition, <100,000 had slightly higher 100,000 both breeds, particularly SCC, where exposure pathogens likely.