194 UTILISATION OF FOOD BY THE ANIMAL [chap. 



Deducting this from the fuel value we get 357-3 — 

 178-6 = 178-7 calories as the heat value of 100 grammes 

 of meadow hay. But from this we have to deduct 40 per 

 cent, for internal work spent in digestion, or 71-5 

 calories, leaving only 107-2 calories as the dynamic energy 

 of 100 grammes of meadow hay. Thus the meadow 

 hay, while it possesses more than half (178 compared 

 with 312) the heat value of the cotton cake — i.e. is more 

 than one-half as effective in keeping up the heat of the 

 animal on a maintenance ration — has yet only about 

 one-third of the value of cotton cake (107 as against 303) 

 towards doing work or putting on increased weight. 



Bearing these principles in mind, we may trace 

 certain simple practical consequences. Rough, coarse 

 fodders like hay or straw, poor grass, roots, etc., serve 

 perfectly well for keeping animals in store condition, for 

 though they require a considerable expenditure of energy 

 for their digestion there is enough margin to carry on 

 the internal work of the body and the whole energy is 

 afterwards available as heat, while the animal has only 

 to be kept warm and is neither working nor increasing 

 in weight. Similarly, animals that are at slow work and 

 are never called upon for any great output of energy in 

 proportion to their weight, can be fed upon bulky low- 

 grade fodders which do not develop any great surplus 

 of energy. But when animals are growing rapidly or 

 are performing heavy and rapid work, then comparatively 

 rich and concentrated foods are necessary, foods which 

 develop a large surplus of energy over that which is 

 required for their digestion. A horse standing in the 

 stable may be fed on nothing but hay, just as a horse 

 out at grass needs only a little hay besides the old grass 

 even in severe winters, but as soon as the horse is 

 worked, instead of more hay it must be given corn of 

 some kind ; and a racehorse, on which great calls are 



