Phenotypic and genetic association between fertility and production in dairy cows

Abstract

Relationships between fertility and production in Dutch Friesian cows were studied for Parities 1, 2 and 3. Interval to first insemination (INT), 56-day non-return rate after first insemination, number of inseminations (maximum of 3) and number of days open (DO) were used as measures of fertility. These measures were related to the production of milk, fat, protein, fat- and protein-corrected milk (FPCM), and to the ratio of fat to protein during the first 100 and 305 days of lactation. Breeding receipts from artificial insemination were matched with milk records. Cows were required to have at least one test-day record and one insemination record. A 2-trait restricted maximum likelihood (REML) procedure for an unequal design was used, according to a model that included fixed effects of herd, year, season, age within parity and genetic group of cow and random effects of sire and error. Heritability estimates were between 0.05 and 0.09 for INT and 0.01 and 0.03 for DO. Small positive phenotypic correlations were found between yield traits and DO and INT. No phenotypic relationship was found between 305-day fat to protein ratio and fertility traits. In Partities 2 and 3, the genetic correlation between INT and 100-day yields ranged from -0.08 to 0.33 and 305-day yields from -0.06 to 0.23. Stronger antagonistic relationships were found between DO and 100-day yields (0.21-0.73) and 305-day yields (0.27-0.76). It was concluded that the correlated response in fertility will reduce the profit of selection on milk production by 5% at maximum.