Colostrum Milk and its Vitamin A Content

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Abstract
The vitamin A content of the colostrum from barn-fed heifers in the first lactation was more than double the vitamin A content of the colostrum from the same cows in the 2d lactation. A 7-fold variation in colostral vitamin A potency occurred in these cows which had been fed identical rations and maintained under uniform conditions. A marked increase in the blood plasma vitamin A conc. of the newborn calf followed the ingestion of colostrum and tended to reflect the concs. of vitamin A present in the colostrum of their dams. With cows isolated from their calves the vitamin A potency of their colostrum of the 1st and 2d milkings was about the same. However, cows which were allowed to remain with their calves and, in addition, were milked out twice daily showed a decided drop in vitamin A potency between the 1st and 2d milking. The intraven. injn. of 10 I.U. of oxytocin at the time of milking in cows isolated from their calves also produced a similar drop in vitamin A potency between the 1st and the 2d milking. The chief drop in concentration of vitamin A in the change from colostrum to normal milk occurred during the first 3 milkings following parturition, thereafter there was a gradual drop in vitamin A conc. over a period of several days to the conc. found in milk produced in mid-lactation.