FEEDS AND FEEDING 



average composition of steers slaughtered at various stages, from birth, 

 up to a weight of 1,500 Ibs., in these experiments: 



Average composition of steers at various stages* 



*Not including contents of the digestive tract. 



The table shows that the percentage of water steadily decreases as the 

 animal matures, falling from 71 per ct. in the calves to 43 per ct. in 

 the 1,500-lb. steer. The percentage of fat increases rapidly during the 

 growth and fattening of the animal, increasing from 4.0 per ct. soon 

 after birth to over 37 per ct. in the 1,500-lb. steer. The protein and 

 ash show less change than the water and fat, but decrease percentagely 

 as the animals increase in weight. Haecker states that the storage of 

 protein by the animal, which is rapid in early life, shows a marked 

 slowing up when the animal reaches a weight of about 800 Ibs. On the 

 other hand, the gain in fat is most rapid after the steer reaches a weight 

 of 600 Ibs. 



125. Origin of body fat. The source of the fat which animals store 

 in their bodies has been the subject of much controversy. Modern 

 authorities agree that the body fat of animals may originate either from 

 the fat or carbohydrates of the food. Scientists still disagree some- 

 what upon the possibility of animal fat being formed thru the decom- 

 position of protein, but the preponderance of evidence favors such forma- 

 tion, as is shown later. 



126. Body fat from food fat. Many experiments have conclusively 

 shown that the fat in food which has been acted on by the digestive 

 fluids in the intestines, may be directly stored in the body tissues when 

 supplied in large quantity. 



Hofmann 21 allowed a dog to starve until its weight had decreased from 

 26.5 to 16 kilograms and the supply of fat in its body had practically 

 disappeared, as shown by the increased decomposition of the protein 

 tissues at that time. For 5 days this dog was fed large quantities of 



"Ztschr. Biol., 8, 1872, p. 153. 



