THE FEED REQUIREMENTS OF FARM ANIMALS 139 



work, can handle but a relatively small amount of roughage. 

 Hence, the greater part of the energy should be furnished 

 in the form of concentrates. 



Horses which have not completed their growth and horses 

 which have a large amount of work to do in a short time, as 

 racing and driving horses, should have larger amounts of 

 protein than those prescribed. 



Requirements for Milk Production. — The average chemi- 

 cal composition of milk is as follows: water, 87.1 per cent; 

 ash, 0.7 per cent ; protein, 3.2 per cent ; fat, 3.9 per cent ; and 

 carbohydrates (milk sugar), 5.1 per cent. As the animal 

 organism does not have the power to construct protein from 

 carbohydrates and fats, the protein of the feed is the sole 

 source of the milk protein. However, the fat of the feed 

 is not the sole source of the milk fat, as cows may produce 

 normal amounts of butter fat on a ration containing only 

 traces of fat. It is probable that the carbohydrates, fats, 

 and any surplus of protein in the feed may all be used for 

 the production of milk sugar and butter fat, although their 

 principal source is the carbohydrates of the feed. 



In formulating a standard for milk production, not only 

 the weight of the cow but the quantity and quality of the 

 milk should be taken into consideration. The requirement 

 for maintenance of course depends upon the size of the cow, 

 while the requirement above maintenance varies with the 

 amount and richness of the milk, i.e. the percentage of fat 

 which it contains. 



The requirements for dairy cattle have been determined 

 more accurately than those of any other class of animals. 

 Among the more recent investigators who have studied the 

 requirements for milk production are Armsby and Van Nor- 



