Optimal combination of traits to estimate the breeding value of herd life using multiple trait model

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Optimal combination of traits was investigated to estimate the breeding value (BV) of herd life using multiple trait model. Data were first lactation records of milk, somatic cell score (SCS) and 9 type traits (feet and legs, chest width, angularity, rump angle, foot angle, rear udder height, udder support, udder depth, front teat placement) from 75,091 cows born between 2001 and 2002 with their pedigree records. Herd life was defined as censored records from birth to 84 months at age of cow. Various fixed effects were considered for herd life (herd-year, calving age), milk and SCS (herd-year, calving month, calving age) and type traits (herd-classifier-classified day, age at classification, lactation stage) in the statistical models. When 9 traits model was used, the highest reliability of the estimated BV for herd-life was obtained from a combination of herd life, milk, SCS, feet and legs, chest width, angularity, udder support, udder depth and front teat placement.