8 Bulletin 81 



protein. Since a pound of fat has from 2.25 to 2.5 times the fuel value of 

 a pound of carbohydrates, it is customary in calculating nutritive ratios to 

 multiply the weight of fat by 2.25, 2.4 or 2.5 and to add the result to the 

 weight of the fiber and extract matter. 



Nutritive ratios are_ termed "narrow," "medium" and " wide." A wide 

 ratio is one affording a relative excess of digestible carbohydrates and fat, 

 a narrow one, comparitively small amounts of these ingredients. Oat straw, 

 for instance, is poor in protein and rich in carbohydrates ; cotton- 

 seed meal, the reverse. The nutritive ratio of the straw is wide, — 1:38.3; of 

 the meal, narrow, — 1:1.0. The method of calculating nutritive ratios is as 

 follows : The amounts of digestible protein, carbohydrates and fat being 

 known by the use of tables of analyses, and digestion coefficients (pages 43- 

 49), the amount of digestible fat multiplied by 2.25 is added to the amount 

 of digestible carbohydrates and the total divided by the amount of digest- 

 ible protein. For example 0.4 pounds fat, 13.5 pounds carbohydrates, 2.3 

 pounds protein ; 0.4x2.25=0.9; 13.5+0.9=14.4 ; 14.4-^2.3=6.3. Nutritive 

 ratio =1:6.3, there being 1 part of digestible protein to every 6.3 parts of 

 digestible carbohydrates and fat. 



Calorie is a term used to express the fuel value or heat value of a mater- 

 ial. A "calorie" is the amount of heat required to raise the temperature 

 of a pound of water about 4° F. 



3. FUNCTIONS OF NUTRIENTS 



Food as a whole may be defined as any material which is capable of 

 forming or of repairing tissue, or of yielding energy. It may perform either 

 or all of these functions and still be food. 



The water content of feeds is a secondary consideration and may be 

 disregarded. 



The ash supplies the mineral portion of the bone and furnishes minute 

 proportions to other tissues. Plentiful amounts are usually present to meet 

 most demands. In exceptional cases, such, for instance, as young animals, 

 hogs exclusively corn fed, laying hens, etc., carbonate of lime (oyster shells, 

 chalk), woodashes, or ground bone form a desirable addition to the ration 

 because of the ash which they contain. 



Protein, as has already been pointed out, differs from the other nutrients 

 in that it is the "flesh former," the machine-maker, the repairer of wear and 

 tear. It may, like the other nutrients, be used as fuel to run the machinery, 

 but this is not a wise or economical use of this most costly nutrient. 



The functions of protein are five fold : 



1. From it are formed flesh, tendons, cartilage, etc., and the nitro- 

 genous part of milk (casein, albumen, etc.) 



2. It forms body fat, and perhaps at times milk fat. 



