8 MASS. EXPERIMENT STATION BULLETIN 357 



Wherever possible, statistical analyses have been made of the foregoing data. 

 The results show that taken individually none of the differences between the 

 groups are significant. However, when the evidence is considered as a whole, 

 the trend although slight is in favor of the group which received the vitamin A 

 supplement. Twenty comparisons of various phases of reproductive function 

 are available for the duration of the experiment and have been summarized in 

 the foregoing tables. Of these, eleven favor the group receiving the supplement, 

 six favor the other group, and three are evenly divided. 



So far as growth and reproduction are concerned, the effect of the supplement 

 seems to be reflected principally in a higher birth weight of the calves and in a 

 smaller percentage of stillborn calves. 



Effect on Milk Production 



The influence of the vitamin A supplement on milk production has also been 

 noted. Records are available for 72 complete lactation periods during the ex- 

 periment. About half of the cows were in the herd previously and their records 

 for 56 complete lactation periods previous to the commencement of the experi- 

 ment are available for comparison with those secured later. The results are sum- 

 marized in Table 6. 



Table 6. — Effect of the Vit.'Mviin A Supplement on Milk Production 



Average Daily Production 



per Cow, in Pounds 



(Corrected*) 



1. Records of all cows during the experiment .... 35.43 30.95 



2. Records during the experiment of cows in the 



herd previously 34.84 28.35 



3. Recordsof Group 2 previous to the experiment . 32.94 32.21 



4. Records during the experiment of cows not in 



the herd previously 35.41 36.11 



♦All milk production records have been corrected individually to the usual standard basis; i. e.,. 

 to twice-a-day milking, 4 percent fat, 305-day lactation; also for age and for length of pregnancy 

 during lactation. Only the corrected values for average daily production are given in the table. 



The apparent effect on milk production as indicated by these results is de- 

 cidedly favorable to the vitamin A supplement. There is, however, no good 

 reaSon to believe that the supplement would cause such large differences in pro- 

 duction, and when the records are carefully analyzed it is found that most of the 

 effect is only apparent. None of the differences are significant, being due to 

 unavoidable irregularities in the make-up of the groups with respect to breed. 

 Since a satisfactory correction for breed differences cannot be applied, the only 



