Relationships between Production Traits and Reproductive Performance in Dairy Cattle

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Abstract
The objective of the study was to investigate the interrelationship between different measures of energy status in early lactation (body-weight changes, milk yield, keto-test reaction, energy deficiency) and reproductive performance in the postpartum period. Altogether 281 lactations of 140 cows from the experimental herd of the Swedish University of Agricultural Sciences were studied. The cows were in first to fifth lactation and of the following Swedish dairy cattle breeds: Swedish Red and White (SRB), Swedish Friesian (SLB), reciprocal F1-crosses of the two breeds, and Swedish Jersey (SJB). A Mixed Model Procedure was used to estimate breed and parity effects, and error and between-cow variance components. Phenotypic correlations between live-weight changes and fertility traits were low. Higher peak- and 120-day yields (in kg energy-corrected milk) were associated with longer intervals from parturition to first ovulation, first ovulatory oestrus, regular reproductive functions and conception, a lower conception rate at first AI and accordingly a larger number of AI per service period. Feed consumption traits followed similar patterns, though these correlations were of slightly smaller magnitude. Keto-test reaction was positively but rather weakly correlated to energy deficiency (0.19) and to days to energy balance (0.23). With larger number of weeks with positive keto-test reactions and a larger energy deficiency intervals to first ovulation, first ovulatory oestrus and regular reproductive functions were longer as indicated by estimated correlations (0.11–0.14 and 0.29–0.30, respectively). Conception rates and calving–conception interval were not related to the energy balance to the same extent. The Jersey breed seemed to have a greater ability to mobilize from body reserves compared with the other breeds. At the same time they resumed their reproductive functions earlier after calving.