title: Effects of inbreeding on milk and fat production, stayability, and calving interval of registered Ayrshire cattle in the northeastern United States.
abstract: Inbreeding coefficients of 30,794 registered Ayrshire cows were calculated from relationships between sire and maternal male ancestors. Average inbreeding coefficient of all cows was less than 1% and of the 5,202 inbred cows was 5.4%. Fewer than 2% of inbred cows had coefficients greater than 15%. Percent of inbred cows increased from 23% of cows born in 1972 to 43% in 1980. Over the same period average inbreeding coefficient of all cows increased from 1.2 to 2.0%, but average coefficient of inbred cows decreased from 5.6 to 4.7%. Effects of inbreeding on first lactation, 305-day, 2X, mature equivalent milk and fat production (kg), 48-mo stayability (proportion of cows surviving to 48 mo of age), and first calving interval (days) were estimated by a model that included fixed effects for herd-year-seasons, sire-maternal grandsire groups, inbreeding, and random effects for sires and maternal grandsires within groups. Inbreeding was included in the model as a classification (six classes according to inbreeding coefficient: 0, 0+ to 5-%, 5 to 10-%, 10 to 15-%, 15 to 25-%, and 25 to 35-% and one class for cows with indeterminate inbreeding). Estimates of differences between inbreeding classes 0+ to 5-% through 25 to 35-% and the zero inbreeding class indicated that milk and fat production decreased with increased inbreeding. Effects of inbreeding on stayability and calving interval were small. Inbreeding was fitted also as a linear covariate. Regressions of milk, fat, stayability, and calving interval on inbreeding coefficients were -23, -1, -.008, and -.095 per 1% increase of inbreeding coefficient.
mesh_terms: D000818:Animals; D002417:Cattle / Q000235:genetics* / Q000502:physiology; D005260:Female; D007178:Inbreeding; D007774:Lactation; D050356:Lipid Metabolism; D008136:Longevity; D008297:Male; D008892:Milk / Q000378:metabolism*; D008957:Models, Genetic; D010375:Pedigree; D011247:Pregnancy; D012098:Reproduction; D014481:United States; D008055:Lipids
chemical_list: D008055:Lipids