Association between pre-breeding metabolic profiles and reproductive performance in heifers and lactating dairy cows

Abstract Lactating cows and nulliparous heifers are in distinctive and unique physiological conditions when they are approaching the planned time of breeding, at approximately 60 days in milk and 13–15 months of age, respectively. This study aimed to profile the metabolic milieu in heifers (N = 14) and lactating cows (N = 15) in the weeks leading up to planned time of breeding. All cows were followed for a period of 15 weeks, from 3 weeks pre-calving to 12 weeks post-calving, while heifers were monitored for a period of 4 weeks leading up to the tentative week of breeding (pre-breeding period). For data analysis, we further divided cows into primiparous (N = 8) and multiparous (N = 7) cows owing to the significant difference in their milk yield. Assessment of reproductive performance showed that primiparous and multiparous cows tended to have lower pregnancy rates compared to heifers (P