COMPOSITION OF MILK. 45 



VARIATION OF MILK CONSTITUENTS. 



The fat is the most variable portion of milk. It 

 may vary from two to ten per cent with individual 

 cows. Herd milk will seldom vary more than one- 

 half of one per cent, from day to day. The chief 

 causes of variation in the percentages of fat in cows' 

 milk are : the individuality, breed, frequency of milk- 

 ing, night's or morning's milk, period of lactation, 

 care and comfort of the cow, and to a very slight 

 extent, possibly, the feed of the cow. 



The more frequently cows are milked the higher 

 will be the percentage of fat in their milk. As the 

 period of lactation advances, the milk usually be- 

 comes richer in fat and total solids. The better care 

 the cows receive, and the more comfortable they are 

 made, the more favorable are the conditions for 

 secreting rich milk. Whether cows are " stripped " 

 or not will also make a difference in the fat content 

 of milk. Manipulation of the udder will also increase 

 the percentage of fat in the milk. 



Feed, however, has very little, if any, influence on 

 the percentage of fat in milk. Feed influences the 

 quantity, but not the quality, except in rare cases. 

 The cow governs the richness of the milk, hence rich 

 milk must be got by breeding and selecting the cows, 

 rather than by depending upon feed for this purpose. 



The solids not fat are fairly constant in all samples 

 of milk, tending to increase slightly with, but not in 

 the same proportion as, an increase in the percentage 

 of fat. 



Casein is similar to albumen in chemical composi- 



