To Feeds and Feeding. 



II. Growth, Maintenance, Fattening. 

 1. Growth. 



94. Flesh formation. — The lean-meat tissues of the animal body- 

 are composed mostly of muscular fibers. Any increase of flesh 

 tissues can be caused solely by an increase in number or by the 

 thickening of these fibers. These fibers increase in number by 

 dividing lengthwise, which process occurs with farm animals only 

 while young and growing. The fibers of the muscles can thicken 

 to a limited extent only, and hence the muscular tissues, or lean 

 meat, of the mature animal cannot be increased beyond a narrow 

 limit. 



According to Rubner,^ the storage of protein tissue by mature 

 animals is accompanied by more rapid breathing, a rise in temper- 

 ature, and more rapid oxidation of the circulating protein. Kell- 

 ner^ states that a full-grown 66-lb. dog may easily store 2 lbs. of 

 fat in his body without the food reciuirements or bodily functions 

 being materially changed. If the same amount of protein, having 

 but one-half the energy value of the fat, is built up into protein 

 body tissue, an extraordinary amount of food and energy must be 

 expended, and marked changes will then be observed in the be- 

 havior of the animal. Nearly all the protein consumed by mature 

 animals which are neither pregnant nor producing wool or milk is 

 burned or broken down in the body, yielding heat and energy, or 

 is partially decomposed and forms fat and glycogen, which may 

 be stored in the body. Mature animals do not store over 10 to 15 

 per ct. of the digested protein as protein tissue, and often none 

 at all. 



The bones are partly and the muscles, ligaments, tendons, nerv- 

 ous system, and viscera of animals almost wholly protein. During 

 youth all these parts of the body steadily increase in size. Thus 

 growing animals store large amounts of protein in their bodies. 

 Weiske'' found that 5-months-old lambs stored over 22 per ct. of all 

 the protein digested from their food, and Soxhlet* found that suck- 

 ing calves used for the formation of flesh 72.6 per ct. of the digested 

 protein of the milk consumed. The large and long-continued stor- 

 age of protein in young animals does not cause changes in the body 

 which lead to increased oxidation, such as occur in mature animals. 



^ Gesetze Energieverbrauch, 1902, p. 305. 



= Ernahr. landw. Nutztiere, 1907, p. 119. 



' Landw. Jahrb., 9, 1880, p. 205. 



* Ber. land. chem. Vers. Stat. Wien, 1878, p. 133. 



