FEEDING UREA TO DAIRY COWS 7 



Changes in Live Weight 



Weights were taken on two consecutive days each month throughout the 

 trials; the changes have been summarized in Table 6. 



Although all the differences in weight favor the regular ration they are small 

 and statistically not significant. However, of the sixty-four individual weight 

 changes on which the average figures in Table 6 are based, four represented losses 

 in weight, and all four of these losses were in cows in the double reversal groups 

 while thev were on the urea ration. 



Total Milk Production 



In the case of the "double reversal" groups comparisons are possible only 

 between the several periods of the experimental lactations as the cows were 

 alternated from one ration to the other. These data are summarized in Table 7. 

 For the "continuous" groups comparisons are possible not only of their relative 

 performance during the actual trial, but also with their performance previous to 

 the start of the experiment. The data for these groups are therefore presented 

 separately in Table 8. All yields reported have been adjusted for the following 

 variables in the usual manner: 



(a) Fat percentage of the milk. 



(b) Length of lactation (305 days taken as the standard). 



(c) Age of the cow. 



(d) Length of time that next calf was carried during the lactation. 



All of the cows were machine-milked three times a day. Accurate records of 

 feed consumption as well as of milk production were kept at all times. 



Table 7. — Milk Production of the "Double Reversal" Groups 



Average Digestible Nutrients 



Corrected Percent Required to Produce 100 



Production of Fat Pounds of 4 Percent Milk 



(Pounds per 



Cow Daily) Nitrogen* Total 



(Pounds) (Pounds) 



Regular Ration 



First year 41.4 3.28 8.25 69.54 



Second year 43.2 3.26 8.38 66.68 



Urea Ration 



First year 39.7 3.29 8.38 71.14 



Second year 41.1 3.16 8.56 69.80 



The number of cow days was 784 in every case: i. e., 

 Number in group (4) X days in week (7) X length of trial in weeks (28) = 784 



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

 on a protein basis. 



Statistical analysis of the detailed data shows that none of the differences In 

 average milk yield reported in Tables 7 and 8 are significant. It must be admitted, 

 however, that the trend from year to year, not only in average yields but also in 

 efficiency of feed utilization, Is unmistakably in favor of those groups which 

 received the regular ration. It will be observed also that although both groups 

 dropped in production to about the same degree from 1939 to 1940, the subse- 

 quent increase in production from 1940 to 1941 was about seven times greater 

 in_the "regular" group than in the "urea" group. 



