e04 ANNUAL. REPORT OP THE Off. Doc. 



would be better if we looked at the matter in a different way. 

 A ratio is always a difficult and misleading thing to deal with, and 

 I think that instead of figuring upon the relation of protein to carbo- 

 hydrates, it would be better to figure on the absolute amount of 

 protein required, that is the actual number of pounds. In running 

 a gasoline engine, a certain amount of repair material is required. 

 It does not make so much difference whether much or little gasoline 

 is used, you have to have about so much repair material anyway. 

 Now, this is even more true in the animal. Under any given con- 

 dition the working machinery of the body wears out at about the 

 same rate whether the food supplies a moderate amount or a large 

 amount of fuel material. There is the difference between the ani- 

 mal and the engine, however, that the former can use surplus 

 repair material for fuel. The repairs in the animal body can only 

 be made with protein, but protein can also be used as a source of 

 energy. It, therefore, does not make any particular difference 

 what proportion of protein you have in relation to the fuel material, 

 provided you have enough pounde of protein for repairs. Take 

 the case of a thousand-pound steer standing quiet in the barn; he 

 will need) about half a pound of protein a day to keep his body 

 machinery in repair. Now, provided you give him a ration that 

 contains half a pound of digestible protein, it does not matter so 

 much whether you give him only that half-pound or whether he 

 gets a pound, or two pounds. He must have the half-pound of pro- 

 tein. If you give him a pound, he will have half a pound which he 

 does not need for repair and which he may use as fuel in place of an 

 equivalent amount of carbo-hydrates or fat. The one ration will 

 do as well as the other, so far as protein is concerned. The second 

 one will give him a little bit more fuel material. It is not nec- 

 essary that there should be some exact proportion of protein, say 

 one part to five and a half or six parts of carbo-hydrates, that is 

 it is not necessary in the sense that the animal cannot use the 

 ration unless it is just in that ratio. What is necessary is that 

 an animal shall have enough protein to supply repair material and 

 normal growth. If he has that, it does not matter so much what 

 you add for the fuel material. Ordinarily, of course, the latter is 

 chiefly carbo-hydrates and fat, but any protein in excess of that 

 needed for repair and growth also serves as fuel material. The 

 whole matter of the balanced ration, then, resolves itself into this: 

 that the food must contain at least a certain minimum amount 

 of protein, varying with the purpose of the feeding, and must supply 

 enough fuel material to run the animal and allow a proper excess 

 for the production of fat if that is desired. In practice, however, 

 protein usually costs more than carbo-hydrates and fat and there- 

 fore we try to use a little protein as possible but it is not the ratio 

 of protein to the other materials which we have to consider as much 

 as its absolute amount. 



It has been shown that in a ration low in protein and with a 

 large proportion of carbo-hydrates there will be a little loss of 

 digestibility, and it has been advised on that account that it is 

 well not to have more than eight or ten parts of carbo-hydrates to 

 one of protein; that is, a nutritive ratio, 1:8 to 1:10. In general 

 It is not wise to curtail in protein at the expense of digestibility, 

 yet it is easy to imagine circumstances under which it would be 



