VITAMIN A FOR DAIRY CATTLE 



Table 



Length of Lactation and Gestation Periods during and 



PREVIOUS TO the EXPERIMENT. 



Average Length 

 of Lactation 



(Days) 



Average Length of Time 



in Calf during 



Lactation (Days) 



Group Group not Group Group not 



Receiving Receiving Receiving Receiving 



Vitamin A Vitamin A Vitamin A Vitamin A 



Supplement Supplement Supplement Supplement 



Records of all cows during 

 the experiment 



Records during the experi- 

 ment of cows in the herd 

 previously 



Records of group 2 previ- 

 ous to the experiment . . 



Records during the experi- 

 ment of cows not in the 

 herd previously 



299 



305 



322 



290 



286 



285 

 329 



285 



200 



200 

 216 



194 



161 



170 



227 



150 



Effect on the Fat Content of the Milk 



Regular monthly herd tests for butterfat have made it possible to study the 

 influence of the vitamin A supplement in this respect also. Because of the lack 

 of uniformity in breed make-up of the groups, already referred to in the section 

 on milk production, the only way that possible effect on fat test can be studied 

 is to compare by breed sub-groups the records before and during the experiment 

 of those cows previously in the herd. This comparison is summarized in Table 9. 



The results in Table 9 show that for all breeds, regardless of the group in which 

 the cows were placed, there was a lowering of the average fat percentage during 

 the course of the experiment. The drop in test is not appreciable except in two 

 cases — the Shorthorn and Jersey sub-groups which did not receive the vitamin A 

 supplement. These two fell off enough so that the average for the whole no- 

 supplement group dropped more than twice as much as the average for the group 

 receiving the supplement. 



The differences on the whole are so small that it has not been deemed worth 

 while to analyze them statistically. It is believed that they cannot be of any 

 significance, and it seems safe to conclude that the vitamin supplement did not 

 affect the fat content of the milk. Attempting to explain the general lowering of 

 fat percentage probably would be futile. Some authorities might attribute it to 

 increasing age, but none of these cows were past their prime when the trial w'as 

 completed. It is well known that age has little if any effect on fat test until a 

 cow gets well along in years. (See Eckles: Dairy Cattle and Milk Production. 

 Revised Edition 1931, pages 425-6). 



