18 EXPERIMENT STATION BULLETIN 351 



planned to compare the utilization of rations both with and without ani- 

 mal protein by means of digestion studies. 



K. S. Morrow, H. A. Keener, S. R. Shimer, N. F. Colovos 



Improving the Solids-Not-Fat Content of Milk by Selective Breeding 



During the year three additional sires were proven, making a total 

 of thirteen: eight Holstein, two Jersey, one Guernsey, and two Ayrshire. 

 New lactation records were added for the ten sires proven during the 

 preceding year, and five of the sires were reproven by adding more dam 

 and daughter comparisons. 



Nine sires increased milk production, four decreased milk production; 

 five lowered fat percentage and eight increased the fat test; nine increased 

 the percentage solids-not-fat and four lowered the percntage solids-not- 

 fat. Placing the sires in groups according to fluctuations in the factors, 

 milk production, percentage butterfat, and percentage solids-not-fat 

 (Ex.: + milk, - per cent fat, -f- solids-not-fat; + milk, - per cent 

 solids-not- fat, etc), and averaging the figures the following results were 

 obtained: two sires: + 1975 lbs. milk, - 0.05 per cent fat, + 0.11 per cent 

 solids-not-fat; two sires: + 1174 lbs. milk, - 0.16 per cent fat, - 0.08 per 

 cent solids-not-fat; two sires: -|- 683 lbs. milk, + 0.05 per cent fat, - 0.09 

 per cent solids-not-fat; three sires: -|- 467 lbs. milk, -|- 0.19 per cent fat, 

 -\- 0.21 per cent solids-not-fat; one sire: - 19 lbs. milk, - 0.17 per cent fat, 

 -)- 0.19 per cent solids-not-fat; three sires: - 898 lbs. milk, -)- 0.28 per cent 

 fat and + 0.27 per cent solids-not-fat. 



These results indicate that the three factors, milk production, per- 

 centage butterfat, and percentage of solids-not-fat, may be inherited sep- 

 arately, and that it is impossible to predict the change in solids-not-fat 

 from the change in per cent fat. 



H. C. MooRE, H. A. Keener 



Studies of Bovine Mastitis 



The effectiveness of segregation for the control of streptococcic 

 mastitis has been studied over a five to six-year period in ten experi- 

 mental herds. Samples of milk from all cows in these herds were ex- 

 amined by laboratory tests for mastitis and the infected cows in each herd 

 determined. Tests were then made at intervals of three months to check 

 on the spread and incidence of the infection in each herd. Tmo herds 

 were established as streptococcic mastitis free; segregation of the infected 

 cows was practiced in six herds; and in two herds no attempt was made 

 to segregate the infected from the mastitis free cows. In the segregation 

 procedure, all the mastitis cows were placed at the end of the milking 

 line or on one side of the barn and these animals were always handled and 

 milked last. 



In the two herds that were established as streptococcic mastitis free, 

 no new infections occurred due to .S. a'jralacticie, the organism causing con- 

 tagious mastitis. One of these herds has remained free for a four-year 

 period and the other for a five-year period. While the incidence of mas- 

 titis infection was appreciabh' reduced in the six herds practicing segre- 

 gation, it was not possible to control completely the spread by this meth- 



