150 THE SCIENTIFIC FEEDING OF ANIMALS 



and carbon consumed, although sometimes they are based on the amount of energy 

 conversion. For technical details the reader is referred to Kellner, Die Ernaehrung 

 der Landwirtschaftlichen Nutztiere (The Nutrition of Domestic Animals). 



The energy contained in the nutrients which animals consume is used up in part 

 by the work connected with the process of digestion (mastication, mechanical and 

 secretory functions of the digestive organs, etc.), by processes of decomposition of 

 various kinds, mechanical work connected with absorption, circulation and assimila- 

 tion, and finally converted into heat. The experiments of Rubner have shown to 

 what extent the various nutrients are able to provide this energy. He found, for 

 instance, that a dog, in order to maintain its energy equilibrium, with the surround- 

 ing air at a temperature at 33° C. (91.4° F.), must consume 140.2 calories in tfie 

 form of pure meat, or 114.5 calories in the form of fat, or 106.4 calories in the 

 form of cane sugar, for each 100 calories of heat given off. Thus the net energy 

 value of meat is only 71.3 per cent of its total energy value, that of fat 87.3 per cent 

 and that of cane sugar 94 per cent. The difference is converted into heat and might 

 be looked upon as loss. 



The act of feeding in itself is thus always attended with heat production. The 

 latter process is always materially influenced by the physical character and the 

 chemical composition of the feed. For example, roughage like straw requires more 

 mechanical work in its mastication and its conveyance along the course of the ali- 

 mentary tract than gruel. According to Zuntz and Hagemann, the mechanical work 

 required by the horse to masticate 1 kg. of meadow hay amounts to 167.4 calories, 

 1 kg. of a mixture of oats and chaffed straw (1:6) requires 64.2 calories, 1 kg. 

 of a mixture of corn and chaffed straw (1 :6) 35.7 calories, and 1 kg. green alfalfa 

 30.4 calories. The work required to digest feeding stuffs free or nearly free from 

 crude fiber, like meat, rice and bread, is about 9 per cent of their total energy value. 

 The total energy value of 1 kg. of oats is 2,622 calories, but the available useful or 

 net energy, which remains after deducting the above mentioned losses which occur 

 in the process of digestion, is only 2,121 calories. That of 1 kg. of meadow hay 

 (total 1,580) is only 699; that of 1 kg. of wheat straw (total 705 calories) requires 

 1,165 calories for the work of digestion, etc., or 460 calories more than it actually 

 contains. The amount of heat produced in the digestion of a liberal "production" 

 ration (for fat or milk production) may be so great that the conversion of the 

 available calories into tissue or energy becomes independent of the surrounding 

 temperature (as in ruminants, for example). On the other hand, the amount of 

 heat produced in this manner in swine, which subsist on milk, tubers, root crops and 

 grain, etc., is much less, owing to the nature of the feed consumed. In swine the 

 surrounding temperature exercises a comparatively great influence on the conversion 

 of the food elements into tissue and energy. The effect of the temperature of the 

 surrounding atmosphere is also less in herbivora kept on maintenance rations con- 

 sisting of roughage like hay and straw that require a great amount of mechanical 

 work in their digestion; in other words, feeds that furnish a large amount of 

 thermal energy. But even under such conditions low external temperatures always 

 call for an increased food supply. 



I. Nutrient Requirements 

 1. Assimilation and Utilization 



Digestion and assimilation (or metabolism) of feed are influenced by 

 species, breed, individuality, exercise, etc. 



Feeding stuffs rich in crude fiber are digested and utilized by cattle to 

 better advantage than by any other farm animals. Sheep come next in 

 this respect, followed by horses and swine in the order named. 



In regard to the utilization of crude protein there is no difference be- 

 tween cattle and sheep and only a slight one in favor of the horse. The 

 same is true of the nitrogen-free extract, but there is a more marked 

 difference in the abiHty of the different species of farm animals to digest 

 and utiHze the crude fat. Roughage like wheat chaff or brewers' grains 

 and distillery slops are utilized much less perfectly by swine than by 



