Genetic parameters for production and fertility in spring-calving Irish dairy cattle

The objective of this study was to estimate genetic parameters for milk production and selected fertility traits in Irish dairy cattle. Data were derived from 74 seasonal spring-calving dairy herds with a potential cow population of 6,783 in the 1999 calving season. The average 305-day yields (kg) of milk, fat, and protein, the concentrations (g/kg) of fat and protein were 6572, 245, 222, 37.6 and 33.9, respectively. Calving to first service interval (CFS), calving to conception interval (DO) and first service to conception interval (FSCO) averaged 72, 90, and 17 days, respectively, while pregnancy rate to first service (PRFS) and number of services/cow were 0.48 and 1.78, respectively. The proportion of cows conceiving within the first 21, 42, and 63 days after start of breeding (PR21, PR42, and PR63) were 0.36, 0.57 and 0.72, respectively. (Co)variance components were estimated for the complete data set as well as a separate analysis for pedigree and non-pedigree herds within the data set. Heritability estimates, using the complete data set, for milk production traits ranged from 0.22 (±0.042) for milk yield to 0.70 (±0.049) for milk fat concentration while heritability estimates for fertility traits ranged from zero for PR21 to 0.03 (±0.017) for CFS and SBFS (start of breeding to first service interval). Heritability estimates were numerically greater than zero for all fertility traits in the pedigree herd data set with the exception of PR21. Only two fertility traits had heritability estimates for the non-pedigree herds, namely, CFS (0.03 ± 0.030), SBFS (0.03 ± 0.030); analyses for the other fertility traits failed to converge. Genetic correlations between production and fertility traits were mostly antagonistic, for example, correlations between milk yield and number of services (0.98 ± 0.35) and PRFS (-0.51 ± 0.61). Results indicate that selection for yield alone may lead to a deterioration in fertility and that future selection programmes should include some measures of reproductive performance