SCIENTIFIC FARMING AT ROTHAMSTED. 389 



will of course affect the percentage of total dry substance which is the 

 sum of the figures given in the three preceding columns. 



We may now consider the relations of the constituents of the food 

 to the constituents stored up in the increase. In the experiments to 

 determine the amount of food and of its several constituents, con- 

 sumed by an animal of given weight within a given time, and required 

 to produce a given increase in live weight, the foods presented a wide 

 range of variation in composition, and the rations were so planned 

 that the animals had a supply of ad libitum food containing more or 

 less nitrogenous substance, that enabled them practically to fix for 

 themselves the relative proportions of the nitrogenous and non-nitroge- 

 nous constituents consumed. In all of the feeding experiments it 

 was found that the amount of food consumed by a given live weight 

 of the animal, within a given tine, and also the increase in live weight 

 obtained from it, depended more upon the non-nitrogenous constitu- 

 ents, or even on the total dry substance, than upon the nitrogenous 

 constituents, which had been generally assumed to be the true measure 

 of nutritive value. In experiments with animals expending their 

 energies in the form of work, the same demand for the non-nitrogenous 

 constituents of the food was observed as in the case of fattening ani- 

 mals. A certain moderate amount of nitrogenous substances was 

 evidently needed in the food, but any increase beyond this required 

 quantity had no influence upon the returns obtained for food con- 

 sumed, either in the form of muscular force in working animals, or in 

 increase in live weight in those that were fattened, or even on the 

 amount of nitrogen contained in such increase. The nitrogen dis- 

 charged in the urine, in the form of urea, was found to have no rela- 

 tion to the activity of the muscles, but it was directly increased by an 

 increment of nitrogenous materials in the food. The age and habits 

 of the animals themselves, when growing or fattening, seemed, how- 

 ever, to determine, to some extent, the proportions of nitrogenous 

 materials in the stored-up increase. 



The average results show that oxen supplied liberally with food of 

 good quality, containing a moderate proportion of grain or other con- 

 centrated food, would consume at the rate of from twelve to thirteen 

 pounds of dry substance * per week for each hundred pounds of their 

 weight, and that one pound of increase in live weight would be re- 

 turned for it. Sheep, of several different breeds, consumed, on the 

 average, about fifteen or sixteen pounds of dry substance of slightly 

 better food per week for each hundred pounds of live weight, and re- 

 turned about one pound of increase in weight for each nine pounds of 

 dry substance in their food. Pigs, with food composed largely of 



* Cattle-foods differ widely in the amount of contained water ; the average being in 

 hay from ten to fifteen per cent, in grain from eight to fifteen per cent, and in roots from 

 seventy-five to ninety per cent. The strictly "dry substance," excluding this variable 

 element of water contents, is therefore taken as a basis in estimating nutritive values. 



