146 Maine Agricultural Experiment Station. 1920. 



in the monthly egg record of a hen as a measure of her year 

 record. 



The relation of the average butter-fat percentage of one 

 lactation with the butter-fat percentage of five lactations is 

 determined. These correlation coefficients range from +0.784 

 ±.028 to 0.862 ±.018. Such high values indicate that with 

 slight inaccuracy the butter-fat percentage of one lactation 

 predicts the butter-fat percentage of the first five lactations of 

 a cow's life. 



Table 4 furnishes a ready means of determining from the 

 butter-fat percentage of the first lactation what the butter-fat 

 percentage of the first five will be for a Jersey herd of similar 

 butter-fat percentage to the herd here studied. 



In a preceding bulletin the discussion of these data was di- 

 rected toward the analysis of the influence of age on the per- 

 centage of butter- fat produced in a given lactation and the vari- 

 ability of this butter-fat percentage with age. In the present 

 bulletin the phase of the problem dealing with butter-fat per- 

 centage of one lactation in relation to that of another lactation 

 will be considered. 



Little or no analysis based on concrete data has been made 

 on this problem, yet obviously on a knowledge of these relations 

 depend the justification for many of the practices now extant 

 in dairy husbandry as well as laying the foundation for the solu- 

 tion of many problems connected with the secretion of butter- 

 fat percentage itself. The existing information concerning 

 butter- fat secretion is largely empirical. It is commonly said 

 that the great butter-fat producing machines of today are due 

 to these cattle breeders using such methods. In the widest sense 

 this is no doubt true although such a mode of procedure tells us 

 nothing about the biological factors underlying the advance in 

 butter- fat percentage, or the laws by which it is governed. In 

 such cases chance and luck play a very important part in the 

 improvement. It is in the removal of these disturbing factors 

 and making the improvement less haphazard that exact numer- 

 ical analysis find their place. The solution of the problems con- 

 nected with butter-fat production are complex and need to be 

 approached from many angles. This section of the present in- 

 vestigation was undertaken in the hope that some knowledge 



