The Nutritive Ratio 291 



For adjusting a maintenance ration to the weight of 

 a steer or horse this method seems to have a plausible 

 basis, but it is evidently less applicable to dairy cows 

 or rapidly growing or fattening animals, for in these 

 cases size is not so largely a controlling factor. 



Again, is there a fixed quantity and proportion of 

 protein from which it is unwise to deviate ? If we 

 are trying to supply the needs of a cow giving twenty - 

 five pounds of milk or of a steer gaining two pounds 

 of body substance daily, there is without question a 

 minimum quantity of food protein absolutely neces- 

 sary in each case, but what these minima are has not 

 yet been closely determined. These necessary quanti- 

 ties are undoubtedly not exactly the same for all 

 individuals, although they are not likely to differ 

 widely between single animals of the same class and 

 productive capacity. It is safe to assert that the pro- 

 tein standards are those which it is practicable to 

 feed and which unquestionably meet the demands of 

 intensive production, but we are not sure that when 

 other conditions are right 10 per cent more or 10 per 

 cent less than the specified quantities would influence 

 efficiency either way; in other words, we have no 

 proof in those cases where 2.5 pounds of protein is 

 the standard for a milch cow that 2.75 pounds would 

 not induce larger production or that 2.25 pounds 

 would not meet all requirements when the carbohy- 

 drates are present in sufficient quantity. 



All this is equivalent to saying that we cannot fix 

 exact nutritive ratios. There is, of course, a min- 

 imum food energy which is essential for sustaining a 



