EFFECT OF VITAMIN A SUPPLEMENTS UPON THE STATE OF VITAMIN A IN BLOOD SERUM OF THE DAIRY COW AND IN BLOOD SERUM AND LIVER OF ITS NEONATAL CALF

It has been observed that when cows received concentrates of natural vitamin A ester during the terminal month of gestation their new-born calves possessed greater blood and liver reserves of vitamin A than did calves from dams receiving a standard ration, either with or without the addition of pasture grasses (1).Conceivably the state of this vitamin in the blood serum of the supplemented cows might be different from that normally present.If the placental membranes exhibited differential permeability to the various states of vitamin A in the blood, the form of vitamin A in the ration of the dam might be expected to affect the vitamin reserves of the fetus.The present investigation was undertaken to study the relationship between the form of vitamin A supplement consumed by the pregnant cow and the state of vitamin A in its blood and in the blood and the liver of the new-born calf. ProceduresFeeding and Management-Sixteen pregnant cows and heifers representing four breeds, Holstein, Ayrshire, Jersey, and Guernsey, were used in this investigation (Table I).Starting 4 weeks previous to expected parturition, they were given daily oral doses of 500,000 I.U. of either the alcoholic or the esterified form of vitamin A, the quantity of supplement being doubled 2 weeks later.These cows were part of a group also used in another study, in which additional details of feeding and management practices have been presented (2).Collection of Xamples-Samples of venous blood were collected at the periods indicated in Table I.Most of the blood samples were collected in the morning, allowed to clot, and centrifuged to obtain serum, which was analyzed immediately.The remaining samples were collected in the afternoon before administering the vitamin supplement.Serum from these samples was stored in the dark at 4" until the following morning, when