Seasonal Variations in the Blood Plasma Carotene and Vitamin A of Adult Dairy Cattle

Abstract

Summary Monthly blood-plasma carotene and vitamin A determinations on six mature cows each of the Ayrshire, Guernsey, Jersey, and Holstein breeds were made over a 2-year period. Monthly determinations were similarly made on 16 bulls over an 11-month period. The data show wide fluctuations in blood plasma carotene, as might be expected. The different breeds respond similarly to changes in carotene intake but the extent of change in blood-plasma carotene varies greatly with the breed. The blood-plasma vitamin A varies over rather narrow limits in comparison with blood-plasma carotene. The average monthly range, all breeds considered together, was from a low of 18 micrograms per 100 ml. in June to a high of 24 in October. Breed differences in normal blood-plasma vitamin A are indicated. Changes in blood-plasma vitamin A do not closely follow blood-plasma carotene changes but tend to lag behind. For example, maximum blood-plasma vitamin A values were found about one month after maximum blood-plasma carotene values.