Genetic Change for Clinical Mastitis in Norwegian Cattle: a Threshold Model Analysis

摘要: Records of clinical mastitis on 1.6 million first-lactation daughters 2,411 Norwegian Cattle sires that were progeny tested from 1978 through 1998 analyzed with a threshold model. The main objective was to infer genetic change for the disease in population. A Bayesian approach via Gibbs sampling used. model underlying liability had age at first calving, month x year herd 3-year-period, and sire cow as explanatory variables. Posterior mean (SD) heritability 0.066 (0.003). Genetic evaluations (posterior means) both observable scales computed. Annual bulls born 1973 1993 assessed. linear regression effect birth posterior -0.00018 (0.0004), suggesting nearly constant level mastitis. However, an analysis means by birth-year indicated approximately population 1976 1990 (-0.02%/yr), improvement thereafter (-0.27%/yr). This reflects more emphasis selection recent years. Corresponding results obtained standard -0.01% -0.23% per year, respectively (regression predicted transmitting ability daughters). seems be slightly understated model, assuming holds true.