BULLETIN 286 



THE VARIATION OF MILK SECRETION WITH AGE 

 IN JERSEY CATTLE.* 



John W. Gowen. 

 SUMMARY 



The yield of milk changes definitely with age. The change 

 is a logarithmic change not as commonly supposed a linear 

 change. 



The variation of milk yield from cow to cow also changes 

 definitely with age. This change is described by a parabolic 

 function. 



The curve for growth is logarithmic. The similarity of 

 the two curves suggests the increase in milk production with 

 age could be accounted for by growth of the mammry gland. 



A large body of exact scientific data on milk production 

 has been accumulated since the time of the establishment of the 

 Advanced Registry system of the Holstein-Friesian Association 

 of America and its later adoption by the associations of the 

 other breeds of dairy cattle. These completed records are unique 

 in several ways, chief among which is the fact that the records 

 of the cows included among them must meet a certain standard 

 of performance. This standard for entry has the effect of cut- 

 ting out certain records of cows of the given breed. Thus the 

 Jersey Registry of Merit say that, "if the test is commenced the 

 day the cow is two years old, or previous to that day, she must 

 produce, within one year from the date the test begins, 250.5 

 pounds butter- fat. For each day the cow is over two years at 

 the beginning of her year's test, the amount of butter-fat she 

 must produce in the year is fixed by adding 0.1 (one-tenth) of 



*This paper is an abstract of a longer paper on "Studies in Milk 

 Secretion V. On the Variations and Correlations of Milk Secretion 

 with Age in Jersey Cattle by the same author published in Genetics, 

 March 1920. All literature citations should be made to this complete 

 paper. 



