196 Maine Agricultural Experiment Station. 1920. 



function of age since butter-fat is in truth only the multiple 

 between the milk yield and the butter-fat percentage. 



When the calculations are made it is found that the cows 

 commencing their test under 2 years of age are at the greatest 

 handicap. From two years to four years and six months the 

 handicap becomes progressively less. Between four years and 

 six months and five years the handicap is increased by about 1.5 

 pounds of butter-fat. From five years of age the cow's butter- 

 fat production rises rather rapidly to her maximum yield at 

 about eight years and two months. (This maximum for the 

 butter-fat is somewhat earlier than is the maximum for milk due 

 to the slight decline of the butter-fat percentage with age). From 

 the age of maximum butter-fat production there is a marked 

 decline in the butter-fat as the age of the cow advanced. This 

 decline handicaps the aged cow as compared with one at 7 to 8 

 years old. 



This information allows certain conclusions to be drawn 

 relative to the desirable age at which to commence the advanced 

 registry test for the cow. The most favorable period is between 

 the ages six and one-half years and 9 and one-half years. At 

 this time the average advanced registry cow needs about 80 

 pounds less butter-fat than she would need as a two year old to 

 make a record sufficient for her to enter into the advanced reg- 

 istry. Other differences are perhaps as striking. At the five 

 year old age the requirement for that age gives the average ad- 

 vanced registry cow about thirty pounds of butter-fat handicap 

 over the cow commencing her test as a two year old. 



