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The Correlation between Changes in Age and Milk Production of Dairy Cows under Other than Official Testing Conditions¹

Extension Department, Pennsylvania State College, State College, Pennsylvania

ABSTRACT

1. One thousand six hundred eighty-three yearly records from 475 cows are included in a study of the relation between changes in age and milk production of dairy cows. The records were made in eleven experiment station herds in the United States.
   
2. The Holstein, Jersey, Guernsey and Ayrshire breeds are studied separately.
   
3. Only records made under other than official test conditions are used.
   
4. The age of maximum milk production is found to be eight years for the Holstein, Jersey, and Guernsey breeds and for the Ayrshire, nine years, under the conditions studied.
   
5. The investigation shows that the increase in production is small after six years of age except in the case of Ayrshires which reach maturity one year later than the other three breeds.
   
6. A table is given comparing the percentages of maturity of milk production at the different ages of this investigation with the percentages as shown by records made under other conditions. The chart included the percentages as derived from the advanced register and register of merit requirements of the several breed associations.
   

¹ The material for this article is taken from work preliminary to a thesis by R. S. Clark, for the degree of Master of Science at the University of Minnesota.