MAINTENANCE OF FARM ANIMALS 61 



greatly increases the radiation of heat. Animals with coats wet by cold 

 rain or snow lose additional heat from their bodies, for the cold water 

 which falls on them must be warmed and evaporated by heat generated 

 thru the burning of food. With the well-fed fattening animal, the 

 greater loss of heat thru these causes may not produce any waste of food, 

 for much more heat is being generated in the mastication, digestion, and 

 assimilation of the heavy ration than is normally needed to warm the 

 body. In the case of animals on a maintenance ration, whose chief de- 

 mand is for body fuel, such exposure will necessitate an increased con- 

 sumption of feed to serve as fuel. On the other hand, too high a stable 

 temperature leads to loss of appetite and induces sweating. 



II. REQUIREMENTS FOR PROTEIN 



91. Protein waste from the body. In view of the high cost and relative 

 scarcity of crude protein in feeding stuffs, it is important to know the 

 minimum amount of this nutrient required for maintenance. There is 

 at all times an excretion of nitrogen from the animal body by way of the 

 urine. With a well-nourished animal this excretion is relatively large, 

 the amount depending chiefly upon the quantity of nitrogen supplied in 

 the food. If all food is withheld from such an animal, the nitrogen ex- 

 cretion decreases rapidly at first, until the supply of ammo acids in the 

 blood and tissues, which have not yet been built into body protein, is low- 

 ered to a minimum. The nitrogen waste in the urine then slowly decreases 

 until it reaches a level which remains quite constant so long as heat and 

 energy are furnished by the body fat. When the supply of the latter 

 begins to fail, the muscles and other protein tissues must thereafter not 

 only furnish protein for the repair of the vital body machinery but must 

 also supply the necessary heat and energy ; consequently they waste more 

 rapidly until death follows. 



When animals are fed exclusively on nitrogen-free nutrients, such as 

 the sugars, starches, fats, etc., the waste of fat from the body is materially 

 lessened, and the waste of the nitrogenous tissues of the body, such as 

 the muscles, is somewhat reduced, tho not entirely stopped. On account 

 of this sparing of the body substances, animals forced to live on such 

 diet survive longer than those wholly deprived of food. Yet because of 

 the continuous small waste of protein from the tissues of the body, 

 animals nourished solely on fats and carbohydrates cannot long survive. 



92. Feeding protein alone. We might expect that when protein only 

 is fed to a fasting animal, in an amount corresponding to the quantity 

 lost daily during starvation, it would replace the protein wasted from 

 the tissues, and the animal thus be brought to nitrogen equilibrium ; that 

 is, it would excrete as much, but no more, nitrogen than was contained 

 in the food. However, when protein is fed under such conditions, the 

 amount of nitrogen excreted at once rises, and tho the loss of nitrogen 

 from the tissues is reduced, nitrogen equilibrium is not reached. When 



