Vitamin A supplementation of Holsteins at high concentrations: progesterone and reproductive responses

Five trials involving 168 Holstein cows and 20 heifers were conducted to determine the effect of vitamin A supplementation at high concentrations, 1 or 2 million IU, compared with 100,000 IU/d, on peripheral concentrations of progesterone and on several measures of reproductive performance. Supplemental vitamin A at high concentrations had no effect on circulating concentrations of progesterone in either cyclic or pregnant cows or on most measures of reproductive performance examined in trials. Thus, it was concluded that providing vitamin A at these high concentrations is not warranted.