MASS. EXPERIMENT STATION BULLETIN 406 



Table 8. — Milk Production of the "Continuous" Group 



Average Digestible Nutrients 



Number Corrected Percent Required to Produce 100 



of Cow Production of Fat Pounds of 4 Percent Milk 



Days (Pounds per 



Cow Daily) Nitrogen* Total 



(Pounds) (Pounds) 



(a) Comparisons on Six Cows Only in Each Group** 

 Regular Ration 



1939 1.808 42.34 3.33 



1940 1,491 36.13 3.35 



1941 1,744 42.61 3.34 



Urea Ration 



1939 1,879 44.37 3.33 



1940 1.511 38.11 3.39 



1941 1,714 39.06 3.25 



(b) Comparisons on All Eight Cows in Each Group 



Regular Ration 



1940 2,067 37.52 3.35 7.38 62.92 



1941 2,330 42.22 3.32 7.00 62.62 



Urea Ration 



1940 2,075 38.79 3.36 7.00 60.34 



1941 2,345 40.36 3.24 7.44 66.54 



*Expressed as nitrogen rather than as protein, since the nitrogen of urea cannot be reckoned on 

 a protein basis. 



**The 1939 records were made previous to the inauguration of this work, and are included here 

 only for comparison. Although there were eight cows in each group during the entire trial, only 

 six can be used for this comparison because two of the eight were first-calf heifers in 1940 and hence 

 had no records in 1939. Also, because detailed feed consumption records were not kept prior to 

 the beginning of the trials in 1940, no statement can be made in this part of the table regarding 

 nutrients required to produce a given quantity of milk. 



Shrinkage in Milk Flow 



This criterion has been studied from two angles; (a) using the records from the 

 "continuous" groups, the average percentage shrinkages from month to month 

 in both years have been used to construct the graphs shown in Figure 1 ; in these 

 graphs the individual monthly values have been fitted to a straight line by the 

 method of least squares in order to bring out more clearly the trend of the data; 

 (b) using the records from the "double reversal" groups the relative shrinkages 

 in milk flow when the cows were shifted from one ration to another have been 

 summarized in Table 9. 



In the lactation immediately preceding the experiment (Fig. 1, 1939), the 

 cows which later received urea for two years (Group C), maintained their per- 

 sistency of milk flow at a somewhat higher level than did those cows which later 

 received the regular ration (Group D). However, as the feeding trial progressed 

 through 1940 and 1941 this superiority of Group C was progressively lessened, 

 until at the end of the 1941 lactation the difTerence in favor of Group C was 

 about one fourth of what it had been two years previously'. Analysis of the 

 data shows that none of the difTerences are significant but, as with actual pro- 

 duction, the trend as the experiment progressed is very evident. 



In the "double reversal" groups (Table 9), the shrinkages when the cows were 

 shifted from the urea ration to the regular ration were consistently somewhat 

 less than when they were shifted from the regular ration to urea. Although the 

 differences probably are not significant, the trend is similar to that noted in the 

 "continuous" groups; out of a total of thirty-two comparisons available, twenty- 

 two were in favor of the regular ration. 



