June, 1940] AGRICULTURAL RESEARCH IN N. H. 31 



forty-eight of the bovine cultures were isolated from the milk of 

 cows infected with staphylococcal mastitis and 57 from the milk of 

 apparently healthy animals. 



The coagulase test and hemolysis of blood agar and blood broth 

 proved to be the most consistent and reliable reactions for the differ- 

 entiation of bovine staphylococci, and the cultures studied could be 

 classified into three groups (I, II and III) on the basis of these tests. 

 Considerable information regarding the pathogenicity of these or- 

 ganisms could also be obtained from these reactions. Sheep's plasma 

 was as satisfactory as human plasma for the coagulase test. All 

 coagulase-positive cultures hemoh-zed blood broth and none of the 

 coagulase-negative organisms produced hemolysis in this medium. 

 All toxin-producing strains tested formed either alpha and beta or 

 only beta toxin. Evidence of enterotoxin production by bovine 

 staphylococci was obtained. One hundred and twenty-seven of the 

 146 Group I cultures (87 per cent). 22 of the 34 Group II strains (64 

 per cent), and 8 of the 25 Groaip III cultures (35 per cent) were from 

 cows showing evidence of mastitis infection. 



The cultures of staphylococci from human sources gave similar 

 reactions to the bovine staphylococci in all tests employed except in 

 the production of toxin. Ten of the 19 human strains formed only 

 alpha toxin, whereas all of the toxin-producing bovine cultures pro- 

 duced some beta toxin. 



The incidence of staphylococcal mastitis was as high as 45 per cent 

 in certain herds and it appears that the Group I staphylococci are 

 the most pathogenic. Studies on the use of vaccines, toxins and bac- 

 teriophage for the treatment of this infection are in progress. 



(Purncll Fund) 

 Dairy 



Variability in Milk Solids-Not-Fat 



During the past year attention was concentrated on the study of 

 two specific factors in relation to the problem ; namely, the effect of 

 a change of feed on one of the herds and the study of heredity, re- 

 ports H. C. jSIoore. 



Four-year data on the solids-not-fat content of milk from individ- 

 ual cows in about 50 herds scattered over the state and from the 15- 

 day composite samples kept l:)y a local dairy company indicate: (1) 

 that cows of the higher testing breeds produce milk higher in solids- 

 not-fat than those of the lower testing breeds; (2) that the kind of 

 feed is not a cause of cows producing low solids-not-fat milk ; (3) that 

 the solids-not-fat content of the milk varies from year to year ; (4) 

 that the ratio between fat and solids-not-fat varies from year to year ; 

 (5) that inheritance is an important factor in determining the com- 

 ])Osition of the milk given by a herd ; and (6) that cows affected with 

 mastitis produce on an average milk lower in solids-not-fat than 

 cows free from mastitis. (Purnell Fund) 



Dry-Feed Systems of Raising Dairy Calves 



During the past year eight calves from the university herd have 

 completed their six months' feeding period on experimental rations. 



