416 



ANIMAL BIOCHEMISTRY 



milk, whey, and lower-quality dried skim milk are still used exten- 

 sively in poultry mashes. Whey, as a by-product of cheese making, is 

 also a feeding material, but its consumption has been confined mainly 

 to hogs and poultry. 



Milk is the most nearly complete food known to science. It is the 

 normal secretion of the mammary gland (page 324). Although 

 there are many kinds of milk (Table 16-5), all references here, unless 

 otherwise indicated, will be to cow's milk. 



TABLE 16-5. Per Cent Composition of Milk from Different Species 



Water Casein Albumin Fat Lactose Ash 



Cow's milk varies in composition, particularly in fat, depending on 

 the breed of cow from which the milk is obtained (Table 16-6). Other 

 factors, such as inheritance, individuality, time of milking, and 

 period of lactation, also influence the composition of milk. 



TABLE 16-6. Effect of Breed on Milk Composition 



(Expressed in Per Cent) 



Breed 



Water Protein 



Fat 



Lactose 



Ash 



Total 

 Solids 



Although it is possible to affect the amount of milk produced by 

 underfeeding and overfeeding, it is not possible to produce marked 

 changes in the fat, protein, or sugar content of milk by changes in 

 feeding practice. It is possible, however, within narrow limits, to 



