GROWTH AND FATTENING 69 



While the carcass of the steer killed before fattening contained only 

 18.6 per ct. fat, the first 500 lbs. of gain was nearly half, and the last 

 500 lbs. over three-fourths fat. During the first 500 lbs. of gain, 11.9 

 per ct. of the increase was protein, but in the last 500 lbs. of gain only 

 5.2 per ct. was protein. The storage of ash was likewise less as the 

 animal matured. 



How body fat is formed. — Since fattening is chiefly a storage of 

 body fat, in studying the feed requirements of fattening animals it is 

 most important to learn from what substances in the feed this body 

 fat may be formed. By numerous feeding experiments it has been 

 shown that after enough nutrients have been supplied to maintain the 

 body, any excess — no matter whether fat, carbohydrates, or protein — 

 may be transformed into body fat. 



The fat in the food. is not commonly stored in the body without 

 being altered. As a result, even when all are fed the very same feeds, 

 the fat formed by the steer, sheep, and pig will differ considerably in 

 chemical properties. All the digested fat taken into the body beyond 

 that required for maintenance cannot be deposited as body fat, since 

 considerable losses always occur thru the energy used up in digestion 

 and assimilation. The largest part of the fat stored in the body is 

 undoubtedly formed from the carbohydrates of the food, for these are 

 the most abundant nutrients in all common rations. When more pro- 

 tein is furnished than is needed for the repair of the body tissues, the 

 remainder may, after the nitrogen is split off, also be changed into 

 body fat. 



The ration for fattening. — Since the fattening of mature animals, 

 consists mainly in the storage of fat, there is no demand for a large 

 supply of protein for fattening animals. However, it is not advis- 

 able to feed a ration having a wider nutritive ratio than 1 :10 or 1 :12, 

 for, as we have seen in Chapter III, when less protein than this is fed 

 the digestibility of the ration is decreased. Since any excess of pro- 

 tein can be changed into fat, where protein-rich feeds are cheaper 

 than those of a carbonaceous character, it may be profitable to feed 

 rations having a narrow nutritive ratio. For example, in the South, 

 where cottonseed meal is frequently the only concentrate used, fatten- 

 ing steers are often fed rations having nutritive ratios of 1 :4, or even 

 narrower. Animals in thin flesh should at first receive a liberal sup- 

 ply of protein so that their muscular tissues may develop. 



Because young animals make the most economical gains, most of 

 the meat-producing animals in this country are fattened and mar- 

 keted before maturity. Such animals add not only fat but also con- 

 siderable lean meat to their bodies as they fatten, and therefore re- 



