VITAiMIN A FOR DAIRY CATTLE 3 



until tht' L-nd of April 1937. Records arc available for nineteen months of con- 

 tinuous feeding of the supplement (October 1, '35 to April 30, '37) and for a 

 total of twenty-two months altogether. Approximately 150 individuals were 

 included, 70 of which were on trial during the entire course of the experiment, 

 either as milking cows or as heifers and later as milkers. 



A double control on the efficacx' of the supplement was established. Approx- 

 imately one half of the heifers and one third of the milking cows were not given the 

 supplement, and in addition the recoids of the older cows, for a period of several 

 \'ears previous to the commencement of the experiment, were available for com- 

 parison with the results secured during the trial. 



The feeding and management^ of the herd was the same as has been followed 

 for years: viz., pasture from about May 1st to about Sept. 30th, and barn feeding 

 from October through April, which included in addition to grain, mixed hay of 

 average cjuality, liberal amounts of corn silage, and a fair allowance of mangels 

 or beet pulp. Grain was fed at about an average ratio of 1:3, except when the 

 cows were on pasture when it was reduced to about 1 :7 or 8. The heifers did 

 not receive an\' mangels or beet pulp and their grain allowance was 4 to 5 pounds 

 per head daily. They did not receive grain while on pasture from May to October 

 of both years. The protein level of the grain was adjusted from time to time as 

 circumstances warranted. 



Table 1. — Average Daily Rations per Cow during the Barn Feeding 



Season of 1935-1936 and 1936-37, together with the Average Carotene 



Content of the Feeds. 



.Average Pounds Average Carotene 



per Cow. Daily per Pound of Feed 



Hay 6.6 2,188 gamma of carotene* 



Rowen 3.0 1,588 do. 



Corn silage 33 8 2,063 do. 



Roots 10.3 None 



Beet pulp 1.7 None 



/- • ,, ^ ; With supplement 3,120** U.S. P. units of Vitamin A 



(^Without supplement. None 



*One gamma of pure beta carotene is equal to 1.6 U. S. P. units of Vitamin A. 

 **By actural assay. The amount on the basis of guaranteed potency ot the supplement was 

 2.835 U. S. P. units per pound. Evidently a reasonable margin of safety was allowed. It is also 

 evident that in this particular lot of grain, at least, there was a minimum of destruction of the 

 vitamin in storage. 



The vitamin A concentrate which part of the herd received was incorporated 

 into the grain mixture at the rate of 0.25 percent (5 lbs. per ton). Except for this 

 addition the grain mixtures were identical at any given time. The supplement 

 used was a fortified cod liver oil. It was mixed first with wheat middlings to make 

 what is known as a "premix," which was then blended with the rest of the feed 

 to give the desired amount of the supplement per ton. Such a procedure is nec- 

 essary wherever such small amounts of a substance are used, in order to insure 

 its uniform distribution throughout the mixture. 



-Acknowledgement is made of the painstaking attention to detail, especially in the keeping of 

 records, of the herdsmen, Thomas Muir and William Smith. 



