VARIATION' OF FAT IN' MILK 75 



Conditions as to care, feeding, etc.. will i)roduce milk that differs 

 wideh' in this respect. The secretor_\- organs ot the mammary 

 gland are the large contrcjlling factor, and these we cannot 

 change. Even in the same l")reed we hnd animals that differ 

 very wiflelv, as the table below, compiled from complete records 

 by Eckles, will indicate. These are a\'erage AX-arh' tests for the 

 highest and lowest testing animals in each breed. 



2. Breed of Cows. —The different breeds of dair\- cattle haA'e 

 their distincti\'e " breed characteristics," and the most important 

 of these are the quantity of milk they produce and its richness in 

 butter-fat. 



The Channel Island breeds — Jersey and Guernsey — are 

 noted for the high fat-content of their milk; the milking strain 

 of Shorthorns and the Ayrshire breed produce a milk of medium 

 richness, while the Holstein produces a milk somewhat lower in 

 fat content. As to quantity of milk produced the order reverses 

 itself. 



For all the breeds, excei)ting the ^lilking Shorthorn, the 

 table which follows, gdving the average production and composi- 

 ti<jn of the milk of the different breeds, is based upon Bulletin 156 

 of the Bureau of x\nimal Hu,sbandry of the U, S, Department of 

 Agriculture, which summarizes and digests the published reports 

 of all the American experiment stations upon this subject. 



3. Time between Milkings. — Where cows are milked twice a 

 day — the common practice in the United States and Canada — 

 the difference in the per cent of fat in the two milkings is quite 

 marked, if the interA'als are very unequal. On the other hand, if 

 the interA-als are equal, or nearly so, the difference is not great. 



