Abstracts. 295 



years. The age to which to predict 'the butter- fat percentage 

 of the other years to arrive at the most nearly accurate result 

 is two years. The correlation coefficients for butter-fat per- 

 centage of a given lactation with the butter-fat percentage of 

 two lactations of which the given lactation is one component 

 range from +0.7048 + . 0343 to ~l-0.9i8idz.0090. 



The correlation coefficients of the butter-fat percentage of 

 one lactation with the butter-fat percentage of the first five lac- 

 tations range from -(-0.784 to -(-0.862. Each regression is 

 shown to be linear by a comparison of the correlation coeffi- 

 cients and correlation ratios. The regression equations for the 

 prediction of the five year butter-fat percentage from the per- 

 centage of any given year are given. 



The difference of the correlation coefficients for one lacta- 

 tion's butter-fat percentage with that of another lactation and 

 for one lactation's butter-fat percentage with the butter-fat per- 

 centage over four lactations has been determined. The differ- 

 ence of these correlation coefficients gives a means of measuring 

 the effect of environmental changes on the butter-fat percentage 

 of one lactation since in the first case the environmental changes 

 of the different lactations as they effect milk production make 

 themselves felt in the correlation coefficients and in the second 

 case the use of the butter-fat percentage for the four lactations 

 give a mean of these environmental effects. The upshot of 

 this comparison showed that environmental changes lower the 

 correlation coefficients from one-seventh to one-eighth of w T hat 

 it would be under the conditions of an average environment. 

 The environmental effect on butter- fat percentage is conse- 

 quently about the same as the environmental effect on milk pro- 

 duction. Since the internal governing action of the cow for 

 milk production has nearly six times the effect on controlling 

 milk production than has the environmental changes, it follows 

 that this internal mechanism (probably hereditary) plays great- 

 er part in determining what these Jerseys' butter-fat percentage 

 will be than does the environment. 



The equations to predict the butter-fat percentage of the 

 first five lactations from the butter-fat percentage of a single 

 lactation are of great importance in culling mediocre cows from 

 the herd. The use of these equations is illustrated. 



