PRINCIPLES OF STOCK FEEDING 



55 



built up by tbe animal body and depos- 

 ited as fat. This was conclusively proven 

 by Lawes and Gilbert in experiments 

 with swine and sheep in which the 

 amount of fat gained in the case of 

 swine was 40 to 80 per cent greater than 

 could have been obtained from the pro- 

 tein and fat contained in the ration. 

 Jordan has also shown that milk fat 

 may be largely derived from the car- 

 bohydrates of the blood. It is thor- 

 oughly well settled at this time that the 

 carbohydrates are a very prominent 

 source of all animal fats. 



Fats then may be derived from the 

 protein in the food, from the fat in the 

 food or from the carbohydrates in the 

 food. It is probable that in fattening 

 animals a very large proportion of the 

 gain in body fat is derived from the 

 carbohydrates. 



When carbohydrates or fat are fed 

 to animals in excess of their daily re- 

 quirements, it is within limit stored 

 in the body as fat. The fat serves as a 

 reserve source of energy and fuel which 

 can be used by the body in time of need 

 or when the food supply is insufficient. 

 Starvation and death do not usually 

 occur until all the stored fat of the body 

 has been used up. 



PRODUCTION OF ENERGY AND 

 HEAT 



Energy may be defined as the capacity 

 to do work. Whether the work consists 

 in drawing a load, digesting the food 

 eaten or in keeping the body warm en- 

 ergy is expended. Not a muscle is moved 

 without the expenditure of energy. The 

 energy of the body is derived entirely 

 from the energy stored up in the food 

 eaten. The energy of the food was de- 

 rived from the sun while the plant was 

 growing in the field. Under the influ- 

 ence of sunlight the carbon of the air 

 was made to unite in the plant with 

 water, producing sugar, starch, fiber, fat, 

 etc. In the building up of these com- 

 pound substances work was expended by 

 the sun. This work was stored up in the 

 newly formed compounds in the form of 

 potential energy, and it is this energy 

 which the body uses in doing work and 

 keeping itself warm. 



Potential energy ra ay be defined as 

 the energy of position. Work must be 

 expended on the hammer of a pile driver 

 to raise it into position. By virtue of 

 its position it is able in falling to do an 

 amount of work in driving the pile 



equal in amount to that done in raising 

 it into position. The energy stored in 

 the hammer when it has reached its 

 position at the top of the pile driver is 

 known as potential energy. Likewise 

 food compounds contain potential en- 

 ergy by virtue of the work expended by 

 the sun in making them. 



When these food compounds are de- 

 composed or broken down in the body by 

 oxidation or cleavage, the potential en- 

 ergy they contained is released and be- 

 comes active or "kinetic" energy (en- 

 ergy of motion). It is this energy which 

 is the source of muscular exertion, elec- 

 tricity, heat, etc, in the animal body. 



Before growth or fattening or m i]k 

 production is possible there must be food 

 sufficient to supply first the energy and 

 heat requirements of the body. Only 

 the food in excess of the requirements 

 for these purposes can be used for 

 growth and production. 



The energy set free by the breaking 

 down in the body of the constituents 

 supplied in the digested food ultimately 

 takes the form of heat. The conversion 

 of the energy of motion as in work into 

 heat is well illustrated by pounding a 

 piece of iron on the blacksmith's anvil. 

 As the hammer strikes the iron the en- 

 ergy of motion of the hammer is sud- 

 denly checked and the iron becomes hot, 

 the energy of motion being converted in- 

 to heat. When work is done by the ani- 

 mal either externally or internally, heat 

 is produced. 



Production of energy_What constit- 

 uents of the food are most concerned in 

 the production of energy in the body? 

 At first it was thought that the protein 

 compounds were the most important 

 factors. Experiments, however, do not 

 show that more of the nitrogenous com- 

 pounds are broken down during work 

 when large amounts of energy are re- 

 quired than during rest. On the other 

 hand there is a marked increase in the 

 carbon excretion due to the breaking 

 down of carbon compounds with each 

 increase in the amount of work done. 

 There appears to be an intimate connec- 

 tion between work and the carbon 

 compounds as the fats and carbohydrates 

 as well probably as the carbon portion of 

 the protein compounds ; while the rela- 

 tion between work and nitrogenous com- 

 pounds is not so obvious. 



Chief function of food — While food 

 serves to build up tissue and keep the 

 body in repair its chief function is to 



