10 MASS. EXPERIMENT STATION BULLETIN 357 



the supplement. Average production pre\ ious to the experiment for three of the 

 five breeds represented was greater in the group that later did not receive the 

 supplement than it was in the group which received it, although not significantly 

 so. Table 7 will aid in making clearer these differences and trends. 



2. The average production of individual cows before and during the experi- 

 ment has also been compared, with the following results: 



Group Group 



Receiving not Receiving 



the Supplement the Supplement 



Number of cows showing an increase in production 

 during the experiment over their previous pro- 

 duction 18 1 



Number of cows showing a decrease in production. 10 8 



Percentage of total number in group showing an 



increase 64 . 3 11.1 



In fairness it must be stated that, had there been a larger number of complete 

 lactation records available for the group not receiving the vitamin supplement, 

 the result might have been less favorable to the other group. Nevertheless straws 

 show which way the wind blows. 



Everything considered, it seems that the vitamin supplement had a favorable 

 effect on milk production. It is to be regretted that, for reasons already given 

 (see page 8), the extent of this effect cannot be definitely stated. 



The question may be raised as to how this favorable effect made itself manifest 

 in increased production. It is believed that it was brought about b\' a raising 

 of the level of persistency in milk flow in those individuals receiving the supple- 

 ment. In support of this contention the average lengths of lactation for the 

 several groups and sub-groups of cows are listed in Table 8. 



The significant feature of these lactation records lies in a comparison of the 

 figures for groups 2 and 3, before and during the experiment. Previous to the 

 experiment, those cows later receiving the supplement had an average lactation 

 period one week shorter than did those which later did not receive the supple- 

 ment; but this relationship was changed during the experiment so that the cows 

 receiving the supplement had an average lactation period twenty days longer 

 than that of the other group. It should be noted that this greater persistency by 

 the cows receiving the supplement was in spite of the fact that these cows averaged 

 thirty days longer in calf during their lactation than did the others; whereas 

 before the experiment they carried a calf, while milking, on an average eleven 

 days less than the other group did. 



The same general relationship was true also for the young cows in group 4; 

 i. e., a greater persistency in milk yield among those receiving the supplement, 

 despite a somewhat longer period in calf while milking. It may be fairly con- 

 tended that possibly those young cows receiving the supplement had a better 

 inheritance foi persistency than those that did not receive it, but the results are 

 presented here nevertheless as showing the same general trend as those for group 

 2, against which, as shown above, such a contention does not hold. 



The data for group 1 are listed only for the sake of completeness. Since they 

 are a composite of those for the other groups, it naturally follows that they would 

 show the same general trend. 



