Studies in Milk Secretion. 105 



There is slight variation in the average per cent of fat between 

 two, three and four-year olds, and full aged cows. 



The highest per cents of fat usuall}^ follow the shortest period 

 between milkings. The lowest per cents of fat usually follow 

 the longest period between milkings. Where the cows are 

 milked at equal intervals the highest per cent occurs most often 

 at or near the noon hour, and the lowest per cent about equally 

 often at morning and night with a much larger number at mid- 

 night than at noon. 



. The average range of variation during seven days between the 

 highest and lowest per cen'ts of fat for individual animals is 

 greater among four-year olds and full aged cows than among the 

 vouno:er animals. 



Neither the cows which show very great variation during 

 seven days in the per cent of fat nor those which show slight 

 variation are abnormal animals, since their total product of milk 

 and fat is near the average for their class. 



Cows which have been once tested and forced to their greatest 

 capacity for a week rarely reach the same height of production 

 again during the same period of lactation, even though the cir- 

 cumstances be otherwise most favorable, but frequently have 

 made increased records in succeeding periods of lactation. 



There is an increase of only 7.5 per cent of milk and 7.7 per 

 cent in fat of full aged cows over four-year olds, which shows 

 that, on an average, cows have very nearly reached their largest 

 production between the ages of four and five. 



The "Equivalent Record " plan is supported by the records 

 of individual cows which have been tested at various times from 

 two to five years of age, but not by the average records of all 

 the cows of the different ages. 



