CHAPTER XI 



LAWS OF NUTRITION 



The preceding pages have been devoted to a 

 discussion of the origin of cattle foods, what they are 

 in substance, how their nutrients are made available and 

 how used. So far no attempt has been made to bring 

 together in a concise form what may be called the funda- 

 mental principles or laws of nutrition. It is desirable, how- 

 ever, before passing to the consideration of the practice 

 of cattle-feeding, to summarize the principles on which 

 the science of cattle-feeding is based. 



280. All energy and buUding-material applied to the 

 maintenance and growth of the animal body come from 

 the food, water, and oxygen being included in this term. 

 The animal originates neither energy nor matter. 



281. Only that portion of the food which is digested, 

 i. e., that which is rendered soluble and diffusible by the 

 digestive fluids so that it passes into the blood, is avail- 

 able for any use whatever. 



282. The imutUized food and the wastes pass from the 

 body in several directions. The imdigested part mainly 

 constitutes the solid excrement or feces. The urea and 

 other nitrogenous compounds which are the unoxidized 

 portion of the protein, pass out wholly in the urine. All 

 digested nitrogen not stored is found here. The carbon 

 dioxid is eliminated through the skin and lungs, chiefly 

 the latter, and water is disposed of through the kidneys, 

 skin, and lungs. 



(197) 



