58 Maine Agricultural Experiment Station. 1919. 



mental factors play in the production of particular, individual 

 records. It seems perfectly clear that a prerequisite to any- 

 thing approaching a sound hasis for such a judgment is a 

 thorough analytical study, with the hest of biometric tools, of 

 the normal variability of milk and fat production. 



Material 



The present study is based on the records of Ayrshire 

 cattle published in the Reports of the Ayrshire Cattle Milk 

 Records Committee of Scotland, compiled by Speir and Howie. 2 

 Portions of the very valuable records gathered by this Com- 

 mittee have been used by other students of the problems of 

 milk production, notably Wilson, Pearson, and most recently 

 Vigor. 



The reports under consideration include, so far as it is 

 possible to get the information, the following items : 



i. Total milk produced (in gallons). 



2. Average percentage of fat, determined from periodic 

 tests. 



3. Total milk calculated to a 3 per cent fat basis. 



4. Weeks in milk. 



5. Age of cow. 



6. Date of last calving. 



7. Miscellaneous information about the cow, particularly 

 of abnormal circumstances of any sort during the test. 



In the present study all available records from the 1908 

 and 1909 Reports have been used, if they came within the fol- 

 lowing regulations which we established in order to secure 

 critical material for variation study. 



a. The record must be complete in all particulars, (i. e., 



cover items 1 to 6 in the list above). 



b. The record must be based on 32 or more weeks in 



milk. 



c. There must be nothing of an abnormal or unusual na- 



ture about the cow or the lactation, so far as dis- 

 coverable from the records. 



2 It is a great pleasure to acknowledge, with grateful thanks, the 

 kindness of Mr. John Howie of Ayr, Scotland, the Secretary of the 

 Milk Records Committee, in furnishing a set of the Committee's Re- 

 ports for this investigation. 



