SEASONAL VARIATION IN SERUM β-CAROTENE AND VITAMIN A AND THEIR ASSOCIATION WITH POSTPARTUM REPRODUCTIVE PERFORMANCE OF HOLSTEIN COWS

Abstract

Two groups of winter-housed cows (eight cows per group) that calved in winter/spring (Group 1) and summer/fall (Group 2) were used to assess the effect of seasonal variation in serum/3-carotene and vitamin A concentrations on postpartum reproductive performance. The cows maintained adequate levels of serum β-carotene (240 ± 14–339 ± 19 mg dL −1 ) from fall to spring when fed various combinations of hay, silage, haylage and alfalfa pellets. There was an increase (P < 0.05) in serum β-carotene and vitamin A concentrations during summer when the cows were on pasture. Average interval to first ovulation postpartum and services per conception did not differ between the two groups. However, interval for uterine involution, interval to first service and average number of days open were improved in Group 2 cows. Partial correlations were not found between serum β-carotene and vitamin A concentrations during the calving period and any of the reproductive parameters (P > 0.05). Although there was seasonal variation in serum β-carotene and vitamin A concentration, the levels throughout the trial were generally adequate and hence did not affect reproductive performance. Key words: β-carotene, vitamin A, reproductive performance, dairy cows