[Carotene and fluorometrically determined vitamin A levels in the blood plasma of cows in relation to gravidity and type of feeding].

From January to June we determined the concentration of vitamin A and carotene in the blood plasma of 66 high-pregnant cows and cows 23 to 54 days after calving. Seasonal changes and a decrease in the content of both substances before delivery were proved. In field conditions of three farms it was determined that the haylage type of winter feeding was better than the silage type of winter feeding in view of provitamin A supply. The concentration of carotene in blood was always higher with haylage feeding as well as that of vitamin A during the period of high lactation. Regardless of that the level of vitamin A in dairy cows in April and May was lower by almost a quarter compared with feeding fresh green forage in June. The results reveal that the suitable time for assessing the sufficiency of vitamin A supply in cows is the time starting one month after the beginning of lactation. The usability and accuracy of the fluorometric method for determining vitamin A, while respecting the interference caused by phytofluen and beta-carotene, have been proved.