12 Wyoming Experiment Station. 



CRUDE PROTEIN. This subdivision includes a number of 

 compounds, all of which contain nitrogen. The white of an 

 egg, casein of milk, and gelatine belong to this class of bodies, 

 and are designated as proteids. The proteids are tissue-making 

 foods, and they serve to build up the muscles, ligaments, etc. 

 As the tissues must be in healthy condition before an animal 

 can lay on fat, it is desirable that a food should contain a suf- 

 ficient supply of digestible protein. It is an interesting fact 

 that the natural foods for young animals contain a high per- 

 centage of protein. This favors a rapid and healthy growth. 

 In case an animal is fed an excess of proteids, they may be used 

 as fuel in the body or be converted into fat, taking the place 

 of the heat and fat-producing foods, i. e., the fats, starches, 

 and sugars, but no other constituent of food can be converted 

 into proteids, nor take their place. As the proteids found in 

 most forage contain approximately 16 per cent of nitrogen, 

 crude protein is estimated by multiplying the amount of nitro- 

 gent present by 6.25.* All of the nitrogen in the form of 

 amide nitrogen (compounds related to ammonia) is thus cal- 

 culated as part of the crude protein. This does not, however, 

 introduce a serious error, as it has been quite clearly proven 

 that a majority of amides found in plants are oxidized in the 

 same way as other food constituents and may serve some of 

 the functions of the proteids. It is an established fact that 

 they cause a saving of the proteids in the animal economy. 



NITROGEN-FREE EXTRACT consists mainly of starches, 

 sugars, and gums. In the animal metabolism it is used as a 

 fuel and to form fats in the body. The percentage of all other 

 constituents is subtracted from 100 per cent, and the remainder 

 is considered nitrogen-free extract. The name is not distinct- 

 ive, but usage has made its meaning quite generally known. 



*The percentage of nitrogen varies in different proteids and in proteids 

 from different sources, and for this reason quite a serious error may be 

 introduced when the factor 6.25 is used to calculate the proteids from the 

 amount of nitrogen found. This factor is, however, in general use. 



