UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 642 



(Jflf* Contribution from the Bureau of Animal Industry *\| 



Contribution from the Bureau of Animal Industry 

 JOHN R. MOHLER, Chief 



S^h^<^U 



Washington, D. C. 



April 30, 1918 



THE FOUR ESSENTIAL FACTORS IN THE PRODUCTION OF 

 MILK OF LOW BACTERIAL CONTENT. 



By S. Henry Ayers, Lee B. Cook, and Paul W. Clemmek, of the Dairy Division. 1 



CONTENTS. 



Factors influencing the sanitary quality of 

 milk 1 



Objects of the investigation 3 



Description of barn and methods used in the 

 production of the milk 3 



Method of sampling and making the bacterial 

 count 5 



The experimental work 5 



Contamination of milk by unsterilized uten- 

 sils 25 



Contamination of milk by manure and dirt . . . 32 



The three most essential factors in the produc- 

 tion of milk of low baeterial content 38 



A practical demonstration on six farms 39 



Bacterial counts of fresh milk on the average 



farm 43 



The effect of temperature on the growth of 



bacteria in milk 45 



Summary 58 



Conclusions 59 



Literature cited 61 



FACTORS INFLUENCING THE SANITARY QUALITY OF MILK. 



The production of milk of a high sanitary quality involves a 

 knowledge of the influence of numerous factors. Whether these fac- 

 tors are all grouped under one head and considered as a single unit 

 or are grouped into several units, each directly connected with a 

 separate phase of the production of sanitary milk, may not at first 

 thought be of any importance. 



Consideration of that point, however, must lead to the view that 

 to deal intelligently with the factors which influence the sanitary 

 quality of milk they must be grouped in such way as to bring to- 

 gether those which are of importance in connection with a definite 

 phase of production. As an example, the question of abundant light 



x The authors acknowledge their indebtedness to T. E. Woodward, of the Dairy Division ; 

 also to W. R. Hale and W. F. Turner, formerly of this division, who made the work 

 possible through their supervision of the experimental barn. They also extend their 

 thanks to the dairy farmers near Grove City, Pa., and to R. R. Welch, of this division, 

 Who assisted in making a practical demonstration of the work. 

 189§9°— 18— Bull, 642 1 



