Principles and Practice of Stock Feeding 9 



3. It furnishes material for the production of heat to maintain the 

 warmth of the body. 



4. It furnishes material for the production of muscular energy. 



5. It is held by some to be a stimulant to milk production. 



Let us consider these somewhat more in detail. 



1. The primary function of protein is that of tissue-building. This 

 tissue may be the flesh of a growing animal, the repaired or, rather, replaced 

 flesh of a mature beast, the wool of a sheep, or the milk of a cow, which in 

 part at least is made from broken down udder tissue. Without protein no 

 flesh, hair, wool, or milk can be made. Animals fed on materials devoid 

 of this nutrient have starved in the midst of plenty. 



2, 3, 4. The three functions of (2) fat formation, (3) heat making, 

 and (4) the production of muscular energy are usually performed by the 

 fat and carbohydrates of the food. If, however, these are insufficient in 

 amount, protein may be consumed in their stead. Such shortage rarely 

 occurs in cattle feeding except when a ration is deficient in all the nutrients, 

 that is to say when animals are being partially starved. Similarly protein 

 may be used instead of fat or carbohydrates if it is fed in excess of what is 

 needed for making tissue or replacing waste. The protein thus used may be 

 that of the food, or that of the body, i. e. flesh. The more is fed, the more 

 is destroyed by the vital processes, if fed in excess of requirements. These 

 three functions, however, may very properly be termed the secondary func- 

 tions of protein, since these offices can be performed more successfully and 

 more cheaply by the carbohydrates ; and, as has been already observed, in 

 ordinary feeding practice they are more commonly thus performed. 



5. It has long been known that, within certain limits, the more 

 highly nitrogenous the ration, the greater its value as a milk maker. Pro- 

 tein, in other words, seems to act somewhat in the manner of a milk stim- 

 ulant. Average milk carries from 3 to 3.5 per cent albuminoids. A cow giv- 

 ing 30 pounds of milk a day yields therein a pound of protein (casein and 

 albumen) . The fat and milk sugar may be formed otherwise, but casein and 

 albumen can only result from protein feeding. The protein content of a 

 ration more than any other one thing governs its effect upon the milk flow. 



Carbohydrates and fat are so similar in their office in feeding that they 

 may be considered in this connection as one. Their functions are five. 

 They furnish material for the following purposes : 



1. The production of heat. 



2. The production of muscular energy. 



3. The formation of body fat. 



4. The protection of the flesh of the body from too rapid breaking 

 down as a result of vital processes. 



5. The carbohydrates are probably a main source of material for the 

 manufacture of milk fat. 



