Mimeo DH-102
October, 1964
Milk Production Records Make Sense
Willard Dillon, Extension Dairyman
Any characteristic of an animal may be considered as being the sum of environmental effects and hereditary effects. Therefore, we can represent a milk production record as: Environmental Effects plus Hereditary Effects equals Milk Record.
Milk production records, as well as most other economically important characteristics of animals vary greatly because they exist under a wide range of environments and are influenced by many thousands of genes.
It is important to remember that the only part of this equation we can see and measure directly is the actual milk production record. As an example, let us consider a cow with milk records as follows:
Year	Production
	pounds
1960	10,000
1961	12,000
1962	9,000
1963	15,000
1964	14,000
If we add these annual production figures together and divide by five, we find the average record is 12,000 pounds. We know that this cow’s heredity did not change during the years in which she made the records. Since this is true, the variation in these records must result from environmental changes. These environmental changes result from changes in feeding and management. Now, to more easily make use of these records, let us write them as follows:
Year	Average production	Environ. effect	Actual production
	pounds	pounds	pounds
1960	12,000	- 2000	10,000
1961	12,000	0	12,000
1962	12,000	- 3000	9,000
1963	12,000	+ 3000	15,000
1964	12,000	+ 2000	14,000
If we knew that all cows’ average production is 10,000 pounds, we could estimate that the cow we used in this example had received a hereditary effect of 2000 pounds and we could rewrite the records as follows:
Year	Average prod.	Heredity effect	Environ. effect	Actual record
	pounds	pounds	pounds	pounds
1960	10,000	+ 2000	- 2000	10,000
1961	10,000	+ 2000	0	12,000
1962	10,000	+ 2000	- 3000	9,000
1963	10,000	+ 2000	+ 3000	15,000
1964	10,000	+ 2000	+ 2000	14,000
In other words, we can write:
Actual Record = Average of all Records + Hereditary Effect + Environmental Effect.

Each cow’s record has an average part that is common to all records. This is the record that the average cow would make under average environment. It is the point from which we measure favorable (plus) or unfavorable (minus) changes in the hereditary effects and environmental effects.
Dairy Section • Animal Sciences Department
Cooperative Extension Service, PURDUE UNIVERSITY, Lafayette, Indiana