8 



exhaled by the lungs as water and carbonic acid. With its character- 

 istic element — the nitrogen — this is not possible. The nitrogen is 

 transformed into urea, and being of no further use is carried by the 

 blood to the kidneys and excreted as a prominent constituent of the 

 urine*. Experiments have proved that the more protein an animal 

 consumes, the more will be decomposed and changed into heat ; in 

 other words, the quantity of protein consumed, governs the quantity 

 destroyed. At the same time the more protein fed up to a certain 

 point, the greater will be the tendency of the animal to put on flesh 

 or produce milk. Too large an amount of protein cannot be fed, 

 because herbivorous animals are not able to digest and assimilate it ; 

 even if this were possible it would not be economical, the pi*otein 

 being the most costly of the three groups. The animal must have a 

 certain amount of feed to produce heat and energy, and this can be 

 more cheaply secured from the carbohydrates. 



Protein is necessary to replace the wastes of the body, to form 

 flesh, and to enable milk producing animals to give maximum and 

 continuous milk yields. 



Special use of the carbohydrates : The carbohydrates besides 

 being the pi'incipal source of heat and energy, serve as the chief 

 source of fat. 



Special use of the fat : Experiments have proved that fat yields 

 two and one-half times as much heat as the carbohydrates. Animal 

 fat is also formed from the fat of the feed, but as a rule notdirectly ; 

 i. e. the fat molecule is more or less pulled to pieces, and reconstructed. 



The lives of none of our farm animals can be sustained by 

 protein, fat, carbohydrates or ash alone ; and yet protein, 

 carbohydrates and ash of the feed are all absolutely necessary to 

 sustain life and produce growth. Experiments proving the above 

 facts, teach us that for the securing of specific ends, such as the pro- 

 duction of flesh, fat or milk, these several groups of substances as 

 found in our various agricultural plants should not for economical 

 reasons be fed at hap-hazard, but rather in reasonably definite pro- 

 portions, depending upon the end sought 



Digestibility of Feeds : Our observations concerning digestion 

 make it clear that a feed is valuable as a source of nourishment, only 

 so far as its various constituents can be digested and assimilated. 



*The urine or liquid excretion contains from 95 to 98 per cent of water. In 

 solution are urea, potash, small quantities of lime, phosphoric acid, and other 

 more complicated substances. The urineicontains the most valuable half of the 

 total nitrogen, (tor fertilizing purposes) nearly all of the potash, and one-fourth 

 of the phosphoric acid, excreted by the animal daily. 



