Butter-Fat Percentage in Jersey Cattle. 147 



of the intra-individual variation with regard to the relative con- 

 centration of this butter-fat from lactation to lactation would 

 throw some definite light on these problems. The homogeneous 

 nature of the material is especially favorable to this problem. 



Naturally the problem resolves itself into a study of the 

 relative strength and precision of action of the inherited com- 

 plex possessed by the cow working in conjunction with and in 

 opposition to the environmental changes. If heredity plays a 

 large part in the production of a cow the position of the cow in 

 the frequency curves discussed in the earlier part of the paper 

 will remain approximately the same from lactation to lactation; 

 if on the other hand heredity of butter-fat production is weak 

 in comparison with the influence of the shifts in environment, 

 the position in our frequenc}^ curves of the cow will change 

 materially from lactation to lactation. The preliminary steps in 

 the analysis of this problem included a study of the mean butter- 

 fat percentage for each age and the standard deviations of this 

 for the different ages. 



The conclusion which may be drawn from this study of the 

 means, standard deviations and coefficients of variation is that 

 no selection of cows for future milkers on the basis of their but- 

 ter-fat percentage in previous lactations has been practiced at 

 any time in the herd's history. This important conclusion re- 

 garding the data reflects back on the conclusion drawn from the 

 studies of the earlier paper* as those conclusions are freed from 

 the one possible criticism that selection of the best producing 

 animals, to be kept for the milkers in later life, by the records 

 made while they were young, has materially influenced the gen- 

 eral applicability of the results of this study to the herd of Jer- 

 sey Cattle as a whole. 



The Correlation of the Butter-Fat Percentage for Eight 



Months' Milk Yield at a Given Age With the Like 



Butter-Fat Percentage at any Other Given Age. 



The homogeneous nature of the records established by the 

 previous analysis, the data may now be used for the correlations 



*Gowen, John W., 1920. The Variation of Butter-Fat Percentage 

 with Age in Jersey Cattle. In Annual Report of the Maine Agricultural 

 Experiment Station for 1920. pp. 132-144. 



