6 MASS. EXPERIMENT STATION BULLETIN 357 



Discussion 



From Table 2 it will be noted that in most respects tlie reproductive record 

 of the herd as a whole grew worse rather than better during the course of the 

 experiment. The average length of time from calving to first heat increased con- 

 siderably and the incidence of retained placenta was much higher. The only 

 respect in which any considerable improvement was evident was in the average 

 number of services required for conception, which dropped from 2.1 per cow to L6. 

 It is entirely possible that this improvement was due to greater virility in the 

 bulls in service at the time. 



When the data are separated into groups it seems that in some respects the 

 group which received the vitamin A supplement lost less ground than the other 

 group did. The period from calving to first heat was lengthened only four days 

 while for the second group it was lengthened eleven days. There were no calves 

 born dead in the former group while in the latter group there were three. On the 

 other hand, there was a considerably higher incidence of retained placenta in the 

 group receiving vitamin A supplement. Despite the much larger number of cases 

 of milk fever in this group, the ratio "before : during" was not quite as high as 

 in the group which did not receive the vitamin supplement. 



In Table 3 some additional data have been added, records for which had not 

 been kept prior to commencement of the experiment. Also a considerable number 

 of young cows are included here which were not in the herd previously and con- 



Table 4. — Record of Heifers in the Herd during the Experiment. 



Group Receiving 

 Vitamin A 

 Supplement 



Group not Receiving 

 Vitamin .\ 

 Supplement 



Records Number Records Number 



during of during of 



Experiment Records Experiment Records 



Number of individuals. 



Average daily gain in 



weight Pounds 



Regularity of heat peri- 

 ods 



Interval between heats. Days 



Services required for 



conception Number 



Length of gestation. .. . Day? 



Cases of retained pla- 

 centa Number 



Abortions Number 



Calves born dead Number 



Calves died some time 



after birth Number 



