560 NUTRITION OF FARM ANIMALS 



GRADE NET EFFICIENCY 



10% 39% 



20% 3 I% 



30% 2 7 % 



3. FEED REQUIREMENTS FOR WORK 



As is the case in feeding for other purposes, the working animal 

 needs to be supplied with an adequate amount of energy in 

 available form and with certain specific forms of matter, par- 

 ticularly proteins and ash ingredients. 



The requirements of matter 



667. Functions of protein. As shown in Chapter IX (418), 

 the daily protein requirement of the horse for simple mainte- 

 nance is apparently about the same as that of other farm ani- 

 mals, viz., approximately, 0.6 pound of digestible crude protein 

 per 1000 pounds live weight, although the experimental data 

 are rather scanty. 



It appeared in i of this chapter (641-643) that the energy ex- 

 pended in muscular work is practically derived from the katab- 

 olism of carbohydrates and fats, the protein katabolism being 

 unaffected by work so long as'an ample supply of non-nitrog- 

 enous nutrients is available. One might at first thought be 

 inclined to conclude, therefore, that the simple addition of non- 

 nitrogenous material to a maintenance ration would suffice to 

 enable it to support a corresponding amount of work production 

 and that a maintenance ration of digestible protein would also 

 be a sufficient supply for the working horse. Such a conclu- 

 sion would, however, be premature. It is quite conceivable 

 that in order to maintain the muscle as an efficient instrument 

 for converting chemical energy into mechanical work, a higher 

 plane of protein metabolism may be necessary than is required 

 to support it in nitrogen equilibrium when doing no work, 

 while the possibility, for example, of a favorable influence of 

 an abundant protein supply on the blood circulation and on 

 the nervous system should not be overlooked. In fast work 

 especially, the demand of the animal for oxygen reaches a 

 high level. Since the blood is the vehicle by which oxygen is 

 introduced into the body, an adequate stock of blood, or 



