12 MASS. EXPERIMENT STATION BULLETIN 291 



Composition of the Milk 



As already noted on p. 6 the milk of all the cows was analyzed regularly for 

 total solids and fat. A summary of the analyses appears in Table 8. Individuality 

 plays such a large part in determining the average fat and solids test of a group 

 of cows that it would not be fair to claim that any differences between the groups 

 are due entirely to the experimental treatment. In addition, therefore, to the aver- 

 ages for the entire groups during the experiment, which are included largely as a 

 matter of record, Table 8 also contains comparative data which show the average 

 test for a corresponding period previous to the commencement of the experiment 

 of such members of each group as were in the herd at that time and the average 

 test for these same individuals during the course of the experiment. These in- 

 dividuals constitute approximately half of each group. 



Table 8. — Composition of the Milk 



Total Solids Fat 



(per cent) (per cent) 



High Low High Low 



Roughage Roughage Roughage Roughage 



Group Group Group Group 



Entire herd throughout the experiment 11.77 12.33 3.52 3.81 



Cows in herd for a corresponding period 

 previous to the experiment: 



Before the experiment 12.14 11.81 3.71 3.58 



During the experiment 11.70 11.79 3.54 3.62 



Taken at its face value the first group of figures in Table 8 indicates some 

 superiority in fat and total solids in the milk from the low roughage group. Part of 

 this is apparent only, due largely to the presence in that group of a young cow (No. 

 126) that turned out to be an unusually high tester for a Holstein, her milk never 

 testing less than 4 per cent fat and averaging 4.5 per cent over a three-year period. 

 . Asthere wasnot a corresponding high tester in the other group, part of the difference 

 must be charged to this inequality. However, from the second and third sets of 

 figures in the table it seems safe to conclude that part of the difference between the 

 groups in this respect is due to the experimental treatment. While the fat and solids 

 averages for the low roughage group were practically identical for the experimental 

 period and a corresponding period immediately previous to the experiment, this was 

 not the case for the high roughage group. This group showed a shrinkage of 0.44 per 

 cent total solids and 0.17 per cent fat during the experimental period. These figures, 

 representing a large number of individual tests, give evidence that low grain and 

 high roughage feeding may tend to produce milk of slightly lower test as time 

 passes. It does not necessarily follow that the composition of the milk can be sub- 

 stantially changed by any normal system of feeding. 



Reproductive Function 



Two of the cases of retained placenta were in an individual that had had the same 

 trouble twice previous to commencement of the experiment. The case of chronic 

 metritis was also of long standing, having developed prior to the beginning of the 

 experiment. Both cows that aborted reacted negatively to the blood test for infec- 

 tious abortion. 



