VITAMIN A FOR DAIRY CATTLE 

 Table 10. — Vitamin A Potency of Milks. 



Cows receiving the Vitamin A supplement . 

 Cows not receiving the supplement 



It seems clear from these results that the roughage fed during the winter of 

 1937 must have been considerably superior to that fed during the winter of 1936, 

 from the standpoint of carotene (vitamin A) content; also that the supplement 

 was somewhat more effective in raising the vitamin A level of the milk the first 

 year than it was the second. 



In any case it seems apparent that (1) the supplement did increase somewhat 

 the level of vitamin A in the milk, but that (2) the efficiency of the cows in trans- 

 mitting the vitamin A of the supplement or the carotene of the feed to their milk 

 was very low, barely over 2 percent at best, about one third of one percent at 

 worst. This lack of efficiency on the part of cows has been shown by other in- 

 vestigators also, and seems to be characteristic. 



Summary 



The effect on growth, reproduction, and milk production in dairy cattle, of 

 adding to the grain ration a vitamin A supplement in concentrated form, was 

 studied during a period of twenty-two months. 



The entire dairy herd at the State College (young calves and bulls excepted) 

 was included in an extensive feeding trial, one group of cows and heifers receiving 

 the vitamin A supplement, while another group under the same conditions of 

 feeding and management did not receive it. 



Careful records were kept of growth and reproductive function in the heifers 

 and of reproductive function in the cows. Milk records of the cows were available 

 as a matter of routine procedure, also monthly butter fat tests. Vitamin A assays 

 were made of feeds and milk. Reproductive records, milk yields, and fat tests 

 previous to the experiment for those cows previously in the herd, were also avail- 

 able for comparison. 



Results may be summarized as follows: 



1. The supplement was without effect on the growth of heifers past the 

 calf hood stage. 



2. It had a slight, but not significant, favorable effect on reproductive func- 

 tion in cows and heifers. This was reflected chiefly in a higher weight at birth 

 of the calves born to the group of cows receiving the supplement and in a smaller 

 percentage of stillborn calves in that group. All phases of reproducti\e function 

 •considered, the trend, although slight, was in favor of the supplement. 



3. Everything considered, it had a favorable effect on milk production, 

 although for reasons given in the text the extent of this effect cannot be definitely 

 stated. This effect seems to have been brought about through an increased per- 

 sistency in milk flow by those cows receiving the supplement. 



4. The average butterfat content of the milk does not seem to have been 

 affected, either favorably or adversely. 



