THE PHYSIOLOGY OF LACTATION 49 



ingly relax the sphincter muscle which holds the milk in the 

 udder. In practice it has proved profitable to permanently as- 

 sign a certain set of cows to one milker so as to accustom them to 

 his touch. This leads to greater milk production and facilitates 

 work. 



The quantity and quality of milk produced by cows varies within 

 wide limits, differing with the breed and the individual. The fat 

 content especially is subject to much variation. The following 

 figures give some results obtained: 



SUMMARY OF RESULTS OF TESTS OF DAIRY COWS AT THE WORLD'S COLUMBIAN 

 EXPOSITION, CHICAGO, 1893 (ALVORD) 



Pounds of Fat in milk, Cheese made, 



Cows in test. milk. pounds. pounds. 



25 Jerseys 13,296.4 601.91 1451.8 1 



25 Guernseys 10,938.6 488.42 1130.6 \ 15 days in May. 



25 Shorthorns. 



June, July, and 

 August. 



Records of cows in California are given by Anderson as follows: 



Cows. Year. Pounds, milk. Pounds, fat. 



Black erade cow / 1906 7,672.5 361.37 



Black grade cow < Q t i2QA 286.27 



Jersey. 



/1906 6,349.6 260.33 



\1907 6,586.9 270.06 



Hayden gives a large number of records from herds in Illinois. 

 Guernsey cows gave between 5000 to over 12,000 pounds of milk, 

 Holstein-Friesians from 10,000 to over 20,000 pounds, Brown 

 Swiss from 6000 to over 11,000 pounds, and Jerseys 12,000 to 

 over 17,000 pounds during one year. The same author gives the 

 following highest records: 



Cows. Pounds, milk. Pounds, fat. 



Jersey.... 17,253.0 952.00 



Holstein-Friesian 20,165.4 660.75 



Guernsey 12,024.5 . 632.34 



Brown Swiss 10,959.8 455.08 



Alvord gives the following figures as estimates of milk yield 

 by several breeds: Ayrshires average 5500 pounds a year, with 

 maximum of 10,000 to 12,000 pound's; Guernseys average 5000 

 pounds, with maximum of 8000 to nearly 13,000 pounds; Hol- 

 stein-Friesians are very productive, yielding frequently 100 pounds 

 a day, with an annual production of 7500 to 8000 pounds, some- 

 times reaching the enormous figure of 20,000 to 30,000 pounds 

 in a year; Jerseys yield an average of 6000 to 7000 pounds a year, 

 while some produce 9000 ,10,000, 12,000, and nearly 17,000 pounds; 

 Red Polls give an average of 5000 to 5500 pounds, and may give 



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