186 Maine Agricultural Experiment Station. 1920. 



for the advanced registries were drawn up little information 

 "was available as to what real changes were brought about in the 

 •cow's milk yield or butter-fat yield by the advancing age of the 

 cow. In view of this lack of data the herd associations adopted 

 an arbitrary standard. This standard called for the production 

 by Holstein-Friesian cows of not less than 250.5 pounds of 

 butter-fat for the, 365 day period at two years old and for every 

 day that she exceeds two years of age the requirement in butter- 

 fat shall be increased one-tenth of a pound. This increased re- 

 quirement of one-tenth of a pound of butter-fat daily for each 

 day's increase in age shall continue till the requirement reaches 

 360 pounds at the age of five years after which no further in- 

 crease shall be made. Such a standard is obviously a linear 

 function, that is, the cow's possibilities of butter-fat production 

 must commence at 250.5 pounds as a two year old and must go 

 on increasing one-tenth of a pound each day, one uniform step 

 up each day, until she is 5 years old when th\ cow is supposed 

 to be at her maximum productivity. 



One of the first investigations 1 undertaken as part of the 

 animal husbandry investigations of the Maine Agricultural Ex- 

 periment Station was a study of the relation of age to milk yield 

 and butter-fat percentage. In these first studies it was shown 

 that milk yield does not increase with age linearly as was as- 

 sumed to be the case by the Registry Officials. - The increase of 

 milk yield with age was found to be a logarithmic function. 



Since the time when this law was first determined the es- 

 sential conclusion then drawn has been established for milk 

 yields from a variety of dairy cattle under diverse conditions. 

 The seven day milk yields of Jersey cows have been shown to 

 "have a logarithmic relation to age 2 . The milk yield of Ayrshire 

 cows likewise follows the logarithmic law 3 . A pure bred herd 



1 Pearl, Raymond. 1914. On the Law Relating milk flow to age in 

 dairy cattle. Proc. Soc. Expt. Biol, and Med. Vol XII, pp. 18-19. 



2 Pearl, Raymond and Patterson, S. W. 1917. The Change of Milk 

 Flow with age, as determined from seven day records of Jersey cattle, 

 Annual Report of the Maine Agricultural Experiment Station for 1917, 

 pp. 145-153. 



3 Pearl, Raymond and Miner, John Rice. 1919. Variation of Ayr- 

 shire Cows in the Quantity and Fat Content of their milk. Jour. Agric. 

 Research, vol. XVII, No. 6, pp. 285-322. 



