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

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). Although there was seasonal variation i...