Studies in Milk Secretion. 187 



of Jersey cows maintained under the condition of a good dairy- 

 farm follows the logarithmic law in their relation of milk yield 

 to age 4 . The registry of merit Jerseys for their 365 day records 

 have also been shown to change in their milk flow logarithmically 

 with age 5 . 



The necessity for a knowledge of these logarithmic func- 

 tions for the different breeds has been well illustrated by the 

 work of this laboratory for without it no comparison of milk 

 records made at different ages can legitimately be made either 

 for the purpose of determining the value of different sires as 

 shown by the milk yield of their daughters or for inheritance 

 studies. Such studies have already been reported in part for 

 the Jersey 6 and Guernsey 7 breeds and also for inheritance studies 

 on crosses of dairy and beef breeds 8 . The purpose of this paper 

 is to determine the relations of milk yield and butter-fat percent- 

 age to age for the 365 day records of another breed, the Hol- 

 stein-Friesian. These studies have given us the knowledge 

 necessary to determine the transmitting ability of Holstein- 

 Friesian sires. These facts will be published in a later paper 

 of this series. 



The Holstein-Friesian association have collected in their 

 advanced registry work a large number of 365 day records. 

 These year records, volumes 18-28, have been used for a study 

 of the constituents of the milk of Holstein-Friesian cows 9 . The 



4 Gowen, John W. 1920. Studies in Milk Secretion. V. On the 

 Variation and Correlation of Milk Secretion with Age. Genetics, vol. 

 5. 111-189. 



6 Pearl, Raymond, Gowen, John W. and Miner, John Rice. 1919. 

 Studies in Milk Secretion VII. Transmitting Qualities of Jersey Sires 

 for Milk Yield, Butter-fat Percentage and Butter-Fat. Annual report of 

 the Maine Agricultural Experiment Station for 1919, pp. 89-204. 



"Loc. cit. 



'Gowen, John W. 1918. Report of Progress on Animal Husbandry 

 Investigations in 1917. Annual Report of the Maine Agricultural Ex- 

 periment Station for 1918, pp. 205-228. 



1919. Report of Progress on Animal Husbandry Investigations in 

 1919. Annual Report of the Maine Agricultural Experiment Station for 

 1919. pp. 249-284. 



8 Gowen, John W. 1918. Studies in Inheritance of Certain Char- 

 acters of Crosses between Dairy and Beef Breeds of Cattle. Jour. Agric. 

 Research, vol. XV, No. 1, p. 1-57. 



9 Gowen, John W. 1919. Variations and Mode of Secretion of Milk 

 Solids, Jour. Agric. Research, Vol. XVI, No. 3, p. 79-102. 



