Abstract
Barn-housed dairy cows showed the highest blood plasma level of vitamin A (BLVA) in April, May, and June when fed abundant green grass, and the lowest BLVA in February. Their annual average BLVA was 310.2±153.7 IU/dl. The correlation between BLVA and carotinoid level was the highest in the green grass feeding season, when the coefficient of correlation was 0.967.
In grazing dairy heifers, both BLVA and carotinoid level increased with the lapse of time in grazing, and began to decrease when the grazing period was over. The highest BLVA was about three times as high as that estimated immediately before this period.
