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The Rate of Change in the Vitamin A Content of Milk^*

Department of Dairy Husbandry and Research Chemical Laboratory, Purdue University Agricultural Experiment Station, Lafayette, Indiana

ABSTRACT

Studies were made of the rate of change in carotene and vitamin A content of milk fat from two cows following a change from a ration of high vitamin A value to one of law vitamin A value and vice versa. Alfalfa hay was the principal source of vitamin A in the high vitamin A ration while timothy hay was used as the principal source in the low vitamin A ration.

Following the change from a high vitamin A diet to a low vitamin A diet, the milk fat secreted by the cows declined very rapidly in carotene and vitamin A value, reaching an equilibrium level with the ration in about 11 days.

In the repletion period, the carotene content and vitamin A value of the milk fat increased very rapidly to an equilibrium level with the ration ten days after the cows were put on the high vitamin A ration (alfalfa).

It may be concluded that the major effect of a change in the diet upon the vitamin A content of cows' milk can be ascertained by relatively short feeding trials.

^* Published with the approval of the Director of the Purdue University Agricultural Experiment Station.