14 



MASS. EXPERIMENT STATION BULLETIN 406 



In addition to this rather conclusive evidence on the inadequacy of the basal 

 ration some further light is thrown by these later results on the main problem of 

 urea utilization. It has been stated earlier in this section that three of the six 

 cows on the control ration received urea continuously in 1940 and 1941 while the 

 other three were on the regular ration. The relative performance of these two 

 sub-groups on the control ration is shown in Figure 3. The rate of milk shrinkage 

 was in general more rapid in those cows previously on urea than in those previously 

 on the regular ration. The sharp upward trend of the curve from the 27th to 

 the 29th week in group C, and from the 19th to the 20th week in group D, is due 

 to the influence of the alfalfa silage. Group D was about two months behind 

 the other in lactation, which accounts for the effect of the silage showing some- 

 what earlier in that particular graph. It should be noted here also that the addi- 

 tion of urea to the control ration for certain of the cows soon after the feeding 

 of alfalfa silage had been discontinued, did not result in any such positive re- 

 sponse as was noted with the silage. Possibly such a response was too much to 

 hope for at this stage of lactation (the 28th week), but the fact remains that it 

 was not in evidence. 



\ 



cotts f Kim g^Oup t -.rcoulak ^atjon in 1549**1 

 coirs FROu erxKiP c-urca /mt/o/v tn 1940 j. 41 



»£€/( IN LACTATION 



Figure 3. Weekly Shrinkage in Milk Flow on the Control Ration — Season of 1942. 

 For comparison the six cows were divided into two groups on the basis of the ration fed durin)? 

 the two years of the experiment. 



DISCUSSION 



In consideration of the fact that the control ration was demonstrated to be 

 inadequate for milk production, it seems clear that the urea must have been 

 utilized to a considerable extent by the cows; otherwise their performance on 

 the urea ration would have been similar to what it was on the control, since the 

 only difference between the two was the presence (or absence) of urea. On the 

 other hand the cumulative weight of small differences consistently in favor of 

 the regular ration, would seem to indicate just as clearly that for maintenance 



