Genetic and environmental components of semen production traits of arti cial insemination Holstein bulls

A multiple trait procedure allowed joint estimation of model effects and variance and covariance components of semen production of Holstein bulls in artificial insemination. Procedural advantages included rapid iteration and positive definite estimates of covariance matrix. Data consisted of 149,339 semen production records for total sperm, volume, and concentration of ejaculate on 2,351 bulls collected in three bull studs from July 1969 through November 1982. Models defined to describe the biology of semen production included effects for ejaculates, age of bull, ambient temperature, week day by bull barn, scheduling, month by year, colorimeter by calibration period, and bulls. Environmental trends but no genetic trends in semen production were detected. Repeatabilities of measures of total sperm, volume, and concentration of all ejaculates were .26, .23, and .37 and for first ejaculates were .31, .23, and .42 over all studs. Heritabilities were .03, .18, and .10 for all ejaculates and .05, .16, and .16 for first ejaculates. Repeatabilities of first ejaculate measures for bulls collected up to 15 mo and again from 60 mo of age were .21, .27, and .19. Genetic correlations between first ejaculate measures on young bulls and milk and milk fat production in daughters ranged from −.06 to .05.