VARIATION OF FAT IN MILK 



75 



conditions as to care, feeding, etc., will produce milk that differs 

 widely in this respect. The secretory organs of the mammary 

 gland are the large controlling factor, and these we cannot 

 change. Even in the same breed we find animals that differ 

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

 by Eckles, will indicate. These are average yearly tests for the 

 highest and lowest testing animals in each breed. 



2. Breed of Cows. The different breeds of dairy cattle have 

 their distinctive " 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, excepting the Milking Shorthorn, the 

 table which follows, giving the average production and composi- 

 tion of the milk of the different breeds, is based upon Bulletin 156 

 of the Bureau of Animal Husbandry 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 intervals are very unequal. On the other hand, if 

 the intervals are equal, or nearly so, the difference is not great. 



