S Oct., 1907.] Elements of Animal Pliysiology. 587 



Protein is a very important repair food for out of protein most of 

 the solid matter of living cells is composed. A certain amount of protein 

 must be taken in food to cover the constant loss through wear and tear 

 of the body machinery. Protein in excess of this amount is used by the 

 animal as fuel food and it is always advisable to have such an excess. 

 Not all the protein eaten is digested and absorbed ; this is especially the 

 case when the protein is of vegetable origin, part passing through the 

 •digestive tract and leaving the body with the faeces. Carnivores and 

 omnivores obtain rich supplies of highly digestible protein from the animal 

 substances they eat, but vegetable feeders have more difficulty in obtaining 

 their protein. 



The following table gives the approximate percentages of proteins in 

 Tarious foods : — 



Roots and tubers ... ... ... 1 \ — 2 



Most green fodders ... ... 2 — 3 



Cows' milk ... ... ... 2)\ 



Clovers and alfalfa ... ... 4 — 5 



Hay from mixed grasses ... ... 75 



Hav from mixed grasses and clovers ... 10 



Most grains ... ... ... \o\ — 12% 



Wheat bran ... ... ... 16 



Meat ... ... ... 18 



Cotton seed (whole) ... ... i8i 



Flax seed ... ... ... 22\ 



Beans and peas ... ... ... 21 — 34 



As has been stated the proteins vary as regards their digestibility. The 

 animal proteins are almost wholly digested but the vegetable proteins show 

 marked differences in this respect. The percentage of protein digested 

 is relatively high — 70-88 per cent, in grains, seeds, clovers, legumes, and 

 cereal by-products; medium, 50 to 70, in green fodders, hays and silage; 

 and low. 20 to 45, in straws and potatoes. As a general rule the proteins 

 are less digestible the coarser the fodder. A term frequently employed 

 in animal dietetics is the mitritive ratio which means the ratio of the pro- 

 tein in the food to the remaining digestible organic matter expressed as 

 ■carbohydrate.* Nutritive ratios are described as narrow, i to 5^ and 

 under; medium; and wide, i to 8 and over. It has been found by ex- 

 perience that animals thrive better on a certain daily protein intake. 

 Animals at rest or doing moderate work require i^ to 2 lbs. protein per 

 1,000 lbs. live weight, with severe work, or with growing or fattening 

 animals, or in the case of cows yielding over i6 lbs. of milk -per diem, or 

 ewes suckling lambs, 2% to 3I lbs. per 1,000 lbs. live weight are required. 

 It must be clearly understood that only a fraction of what is absorbed from 

 these amounts is required for bodv repair (in the case of a man less than 

 •one-third of the total daily consumption) the remainder being used for 

 energy supply and for the laying on of fat or flesh. 



2. Fuel Foods. — All vital processes require an expenditure of energy 

 which is derived solely from the food. Moreover the animal's temperature 

 must be kept up, and this, too, must be met by the heat produced from 

 the oxidation of food in the body. The more work an animal does, and 

 the colder its surroundings, the more fuel food is required. The energy 



* Fat can be expressed in terms of carbohydrate by multiplying its percentage 

 by 2.4. 



