126 Maine Agricultural Experiment Station. 1920. 



tions at io years and older with those of the younger years range 

 from -f-0.2144zb.0919 to -j-o. 63362!=. 0925. From this brief 

 resume of the tabled results it is seen that all of the results have 

 the plus sign and have a rather large value for data of this kind. 

 The values of the coefficients are in general higher for the 

 younger ages than they are for the older ages. This is a fortu- 

 nate circumstance from a practical standpoint for the breeder 

 is more desirous of selecting the animal to remain in the herd 

 from their two year records than he is to select his animals at 

 ten years old. The values of the correlations are fortunately 

 such that a gain in accuracy results by predicting from the two 

 year olds as over predictions at later ages. 



From the practical side of culling the poor milkers out of 

 the herd these results are highly satisfactory. The data are 

 equally interesting when considered in their biological aspects. 

 The correlation shows that the cows composing the herd are 

 innately differentiated in their milk producing abilities. The 

 plane of production once established the cow tends to maintain 

 this relative plane from lactation to lactation. The value of the 

 correlation indicates clearly that the mechanism behind this func- 

 tion works quite accurately. 



From this point of view it is of a good deal of interest to 

 compare the only other statistics available for cattle with those 

 derived here. Gavin using his measure of the lactation, the 

 "revised maximum." found the correlation between the milk 

 productions of the various lactations "revised maximum." Table 

 2 is a copy of Gavin's table showing these correlations. 



TABLE 2. 



Lactation r with mas. R. M. 



Probable Error 



First +.394 ±0.031 



Second +.452 ±0.030 



Third +.506 ±0.028 



Fourth +.605 ±0.024 



Fifth +.762 ±0.016 



This table shows in general a lower value for the correla- 

 tions measuring the consistency of milking performance from 

 lactation to lactation than is shown on our data. This may in 

 part be due to the fact that Gavin's material was somewhat 



