94 Maine Agricultural Experiment Station. 1919. 



Method of Correcting Records of Milk Production and 



Butter-Fat Percentage at Any Age to the Expected 



Record at Standard Age. 



A knowledge of the function which describes this law al- 

 lows us to calculate what correction should be applied for this 

 mean change in the milk production. The choice of the place 

 to which this correction was to be made was chosen as the maxi- 

 mum production at eight years. The actual maximum mean 

 milk yield comes at 8.12 years as determined by differentiation 

 of the curve given above. These correction factors were de- 

 termined for each three months of age. All the records used 

 in this study have been corrected to their expected production 

 at this constant age of 8 years. The manner in which this cor- 

 rection was made may be stated mathematically as a simple pro- 

 portion. 



Corrected milk at standard age : observed milk at a 

 years :: Mean milk at standard age : mean milk at a years. 



For the animals which have more than one Registry of 

 Merit test, the test which was made nearest eight years of age 

 was used. 



The same general method was used in the correction of 

 the butter-fat percentage records. The theoretical function 

 which describes the relation of age and butter-fat percentage 

 was determined. From this theoretical function, which is a 

 linear one with a slight but consistant decline in the mean but- 

 ter-fat percentage with age, were determined what corrections 

 should be applied to the butter-fat percentage to bring all the 

 records to a constant age basis. The manner in which this cor- 

 rection was used is similar to the proportion shown above for 

 the correction of milk production. The standard age for the 

 butter-fat percentage was taken at two years as this is the age 

 nearest the maximum butter-fat percentage of the cow. 



The butter-fat expected of the cow for these standard ages 

 was determined by multiplying the amount of expected milk by 

 the expected butter- fat percentage. 



All records used for the determination of the transmitting 

 qualities for Jersey sires were based on these expected records 

 at the standard ages. All records referred to in this paper from 



