Use of Food by Growing Animal 325 



is fed for fattening, of .21 to .28 of a pound of actual 

 fat. Here, then, is an actual daily increase of dry 

 body substance of .45 to .61 of a pound, which may be 

 equal to one -fifth or more of the total dry substance 

 of the ration. 



More definite information is furnished by the some- 

 what limited studies which have been made of the 

 metabolism of the calf. As long ago as 1878 Soxhlet 

 studied the income and outgo of three young calves 

 fed on whole milk. One pound of milk solids, prac- 

 tically all digestible, produced one pound increase of 

 live weight, which was equivalent to a storage of at 

 least one -third pound of body dry substance, a food 

 efficiency for growth practically ten times that exhib- 

 ited with animals somewhat mature. Nearly 70 per 

 cent of the protein of the food was fixed in the bodies 

 of these calves, and only a small proportion was broken 

 down, conditions quite the reverse of those which per- 

 tain to the use of food by well -grown steers. Seventy- 

 two per cent of the phosphoric acid and 97 per cent 

 of the lime were retained for the purposes of growth. 

 Later experiments with calves fed on rations in whole 

 or in part composed of skim -milk, show a deposit of 

 from 26 to 43 per cent of the protein. These results 

 illustrate the vigor with which a young animal assimi- 

 lates food for growth, and explain the greater profits 

 from feeding young animals as compared with feeding 

 those more or less mature. 



During recent years there has been much discussion 

 and many experiments touching the influence of food 

 upon the development of the animal body. Several 



