Butter-Fat Percentage in Jersey Cattle. 149 



butter-fat percentage with that of the two years will, of course, 

 be the same (0.5277;+;. 0368) and is repeated in the three year 

 column on the line with the two year age. Such an arrangement 

 facilitates the grasping of the complete picture of the relation 

 between the yield of a given age and that of any other year, as 

 each column represents the correlation coefficients of that year 

 with the other years. 



The largest of these correlation coefficients for the butter- 

 fat percentage of . one lactation in comparison with that of an- 

 other is -f-0.678idz.0310 for the lactation at four years old and at 

 five years old. The lowest correlation coefficient is -f-0.2470 

 zt.0640 for the comparison of the butter-fat percentage of the 

 three year olds with that of the seven year olds. All of these 

 correlations are plus. There was no correlation out of the fifty- 

 six determined which was not significant. Such high' correlations- 

 point to a regulatory mechanism behind the mammary function.; 

 which governs, within certain limits, the concentration of butter- 

 fat which a given cow is able to secrete into her milk from one: 

 lactation to another. In other words the correlations of butter- 

 fat percentage of a given aged cow with that of the other ages; 

 at which this cow may have other lactation records are approxi- 

 mately of the same values throughout. 



The average level of the correlations for butter-fat percent- 

 age of a lactation of a given age with those at any other age is 

 of especial interest to the dairyman since the size of the correla- 

 tion is the index by which he may choose the lactation on which; 

 to base the selection of animals to remain in the herd as future 

 milkers. The averages of these correlations have accordingly 

 been made. The highest average correlation coefficient is for the 

 butter-fat percentage of the lactation commencing between the 

 ages two years to three years (0.5696). The next highest average 

 correlation coefficient is for the four year age (0.5520). The 

 "five year ages is third (0.5514), the eight and nine year age is 

 fourth (0.5156). The other ages at lactation follow in the order, 

 six, three, seven, and ten and older years. The differences in 

 these correlations are of only doubtful significance so that no 

 conclusion as to the relative merit of the use of one lactation over 

 that of another as a basis for selection of animals to remain in 

 the herd, can with certainty be made. Further from the theoreti- 

 cal side no conclusion can be drawn from these figures as to any 



