High β-carotene concentration in plasma enhances cyclic progesterone production in nonpregnant Japanese Black cows.

β-Carotene is an essential nutrient in cattle reproduction. The objective of this study was to evaluate the effect of β-carotene supplementation on ovarian activities throughout the estrous cycle in nonpregnant Japanese Black cows. The estrous cycles of eight nonpregnant Japanese Black cows were synchronized using a double synch protocol, and the cows were divided into two groups. The cows in the β-carotene (BC) group received supplementation with 1000 mg/day β-carotene for 46 days including the synchronization period. The cows in the control (C) group did not receive β-carotene supplementation. The results showed that β-carotene supplementation at 1000 mg/day was sufficient to maintain a high plasma β-carotene concentration and increase the plasma retinol concentration and that β-carotene supplementation had no significant effects on the dominant follicle diameter, total number of estrus behaviors, or length of the estrous cycle. In contrast, the areas under the P 4 concentration curves in the BC group were higher than those obtained for the C group. In conclusion, a high plasma β-carotene concentration in Japanese Black cows promotes P 4 production in the luteal phase of the estrous cycle and total P 4 production throughout the estrous cycle without changing the length of the estrous cycle.