FOOD REQUIREMENTS 373 



Rations vary for different species. According to Murray, 

 the food for crrowins^ cattle should contain as follov/s : — 



3. Fattening. — In the full-grown animal there is no growth 

 of muscle tissue ; the process of fattening therefore consists 

 essentially of changing to fat the food absorbed beyond what 

 is utilised by the animal for its maintenance. It is estimated 

 that when the maintenance energy requirements have been 

 met, about 40 to 50 per cent, of the excess energy of the 

 digestible nutrients of the food can be stored in fat. 



Ordinary food-stuffs contain very little fat. Carbohydrates 

 form by far the most important source of the fat deposited 

 during fattening (p. 351). It is doubtful whether proteins 

 can form fat except indirectly by first being changed to 

 carbohydrates (p. 854), and only certain of the amino-acids 

 yield these. On the average about 50 per cent, of protein 

 is convertible to carbohydrates, the deaminised portion of 

 the remainder being catabolised, yielding heat (p. 272). In 

 cold weather proteins may replace carbohydrates in producing 

 heat — an uneconomical process, as protein is the most 

 expensive constituent of the food. In full-grown animals 

 there is no need for the nutritive ratio to be higher for 

 fattening than for maintenance. If the ratio be kept 

 constant, the increased amount of food will supply all the 

 extra protein that the animal can utilise in the process of 

 fattening. In practice, the percentage of protein is often 

 higher, because many of the concentrated foods used con- 

 tain relatively large proportions of this constituent. It is 

 probable that on a diet with a high percentage of protein the 

 return on the protein in fattening is in increased manurial 

 value rather than in increased fat formation. 



As the object in fattening is to get the greatest increase 

 in weight in the shortest time, the animal is fed to the fullest 



