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, sirematernal 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,

Inbreeding of Artificially Bred Dairy Cattle in the Northeastern United States

“…Characteristics of the data sets are in Table 1 Inbreeding was included in the model either as a classification variable [six classes for cows with known inbreeding coefficients (F): F = 0, 0< F< 5%,5 ~< F< 10%,10~< F< 15%,15 < F < 25%, and F /> 25%; and one class for cows with indeterminate inbreeding coefficients] or as a linear covariate. Further details of the model are in (10). Year-seasons and sire groups were defined as in (10) except that Holstein group size was 100 whereas group size for other breeds was 25.…”

“…Further details of the model are in (10). Year-seasons and sire groups were defined as in (10) except that Holstein group size was 100 whereas group size for other breeds was 25. Heritabilities used in the mixed model equations are in Table 2.…”

“…A partial pedigree including sire of cow and up to seven male ancestors of dam of cows was built for each cow. Relationships among males were calculated by the tabular method (8), and the inbreeding coefficient of each cow was estimated as a function of relationships between sire and maternal male ancestors (10). Cow pedigrees were built with only AI bulls to reduce the size of the relationship matrix calculated.…”

“…First lactation, 2 ×, 305-day, mature equivalent (ME) milk and fat records, calving dates, Sci 67:161--170 161 and stayability information were obtained from DRPL files and subjected to edits described in (10). Characteristics of the data sets are in Table 1 Inbreeding was included in the model either as a classification variable [six classes for cows with known inbreeding coefficients (F): F = 0, 0< F< 5%,5 ~< F< 10%,10~< F< 15%,15 < F < 25%, and F /> 25%; and one class for cows with indeterminate inbreeding coefficients] or as a linear covariate.…”

Genotypic covariance matrices and their inverses for models allowing dominance and inbreeding

“…Moreover, inbreeding depression is a manifestation of interactions like dominance and epistasis. Models which include only additive effects and covariates for inbreeding (eg, Hudson and Van Vleck, 1984) are rough approximations.…”