154 Maine Agricultural Experiment Station. 1920. 



Leghorn pullets the correlation of their monthly productions 

 with their annual production ranges from +0.373 ±.030 to 0.695 

 ±.018. The range of the correlations for butter-fat percentage 

 is 0.784=!=. 028 to o.862±.oi8. The mean correlation coefficients 

 stand in the relation 0.556 to .827 or 1 to 1.49. 



Practical Aspects of the Correlations for Butter-Fat 



Percentage of One Lactation With the Butter-Fat 



Percentage of the First Five Lactations. 



As many of these results have a highly practical bearing it 

 may be well to illustrate one of the uses to which they may be 

 put. The question of what animals shall be saved for milk pro- 

 duction and the perpetuation of the herd is a constantly recurr- 

 ing one in dairy practice. The correlations just deduced in 

 Table 3 show that the basis of this selection should be the rec- 

 ords of the previous lactation. Suppose the herd is composed 

 of 1000 cows which have just completed their first lactation. 

 The equation for this curve 



x 



—9.6974 —1 



x 2 5.2895 Tan 1. 981 7 



y= 17.8901 (1 H ) e 



3.9271 



allows the calculation of the distribution of these one thousand 

 cows as shown in the second column of Table 4. From the 

 eight months butter- fat percentage Table 3 gives the equation to 

 determine the expected mean butter-fat percentage for the first 

 five lactations. The equation is 



B t — i.8i9=t.648b 2 



Where B is equal to the butter-fat percentage of the first five 

 lactations and b 2 is the butter-fat percentage for the first lac- 

 tation. 



The data may be tabled for most easy reference by sum- 

 mation of the number of cows from both ends of the distribu- 

 tion and tabling the butter-fat percentage. This has been done 

 for Table 4. 



