Genetic relationship of functional longevity with female fertility and milk production traits in Czech Holsteins

The objectives of this study were to estimate heritabilities of and genetic correlations among longevity, milk production, and female fertility traits of Holstein cows. Fertility traits were days open, interval from parturition to first service, and days between the first and last insemination in the first and second lactation, respectively. Production traits were first lactation milk, fat, and protein yield. Functional longevity was defined as the number of days between the first calving and culling, i.e. the length of the productive life. The linear animal model included fixed effects of month-year of first calving, regression on age at first calving, regression on milk yield (only for longevity), and random effects of herd-year, animal, and residual. Heritability estimates for fertility traits ranged from 0.02 +/- 0.009 to 0.06 +/- 0.004. Heritability of longevity was 0.09. Heritability estimates for production traits ranged from 0.29 +/- 0.009 (fat and protein yield) to 0.34 +/- 0.009 (milk yield). Genetic correlations of longevity with fertility were moderate and favourable, ranging from -0.37 +/- 0.068 to -0.44 +/- 0.055, except the days between the first and last insemination in the second lactation. Genetic correlations of fertility with production traits were moderate to high and unfavourable, ranging from 0.48 +/- 0.042 to 0.65 +/- 0.034. Substantial herd-year correlations were found between fertility traits. Residual correlations were small except for those between production traits (> 0.85) and between days open and days between the first and last insemination (0.87). Month-year of first calving effects for longevity declined between 1994 and 2002, while those for production traits and for fertility increased slightly or remained stable during this period. Between 1991 and 2003, genetic trend for longevity declined and increased for production. Estimated genetic changes for fertility were unfavourable.