214 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



cording to the nature of the various requests, instructions were given 

 to local inspectors, and authorities were advised regarding local milk 

 ordinances, laboratory control work, and follow-up work. 



Monthly circular letters to milk inspectors have been issued as a 

 means of spreading information calculated to improve milk supplies 

 from the sanitary standpoint. Department Circular 276, " Inspection 

 of Milk Supplies," was prepared with a similar purpose. 



At Grove City, Pa., studies were made of the conditions and 

 methods necessary to produce milk of such quality as to make pos- 

 sible the manufacture of Swiss cheese of high quality by the use of 

 both night's and morning's milk delivered once a day instead of twice 

 a day. From observations made it is apparent that milk of satis- 

 factory quality to make good cheese can be produced on an average 

 farm with once-a-day delivery, and that milk coolers and small-top 

 pails are of great help in improving the quality of the milk, but 

 care must be taken in washing and sterilizing them. 



, MILK-PLANT MANAGEMENT, 



Labor costs and requirements in 75 milk plants in 12 cities were 

 studied, and the results were used as the basis of circular letters 

 known as milk-plant letters, which are given a wide circulation 

 among milk-plant operators. 



Studies on the cream line in milk, as affected by different types of 

 machines, pasteurizing and holding temperatures, cooling, and other 

 processes in milk plants were undertaken in cooperation with the 

 Minnesota State board of health, and some interesting facts have 

 been discovered. 



Many plans for milk plants were sent out during the year, and as- 

 sistance was given to visitors and correspondents in planning and 

 rearranging plants. 



EEQUIREMENTS FOE MILK PEODUCTION. 



Further study was made of records previously obtained in investi- 

 gations of requirements for producing milk, and additional facts 

 were collected for use in preparing a paper discussing basic factors 

 in economical milk production. 



A study of the turnover of cows in dairy herds revealed the fact 

 that the average length of time that a cow remains in a milking herd 

 is 4.2 years. Cows other than those condemned because of tuber- 

 culosis remain for 5.7 years. The difference due to tuberculosis is 

 significant. 



Studies were made of the cost and other requirements for raising 

 dairy heifers in Indiana and Vermont, and the results have been 

 prepared for publication. It was found that in Indiana 48.8 per 

 cent and in Vermont 36.5 per cent of the cost of raising a heifer calf 

 to milking age were incurred during the first six months of her life. 



MILKING MACHINES. 



The cleaning and sterilizing of milking machines and the length 

 of life of the rubber parts were subjects of further study. The 

 method of sterilization by heat was found to give uniformly better 

 results in reducing the number of bacteria in both hot and cold 



