82 PRINCIPLES OF FEEDING FARM ANIMALS 



definitely. According to Kellner/ one hundred pounds of 

 digestible protein in the feed above the requirements of the 

 body for repair and growth produces 23.5 pounds of body fat. 



As in the case of mineral matter, a certain amount of pro- 

 tein is absolutely essential not only for the satisfactory 

 development of the animal but for life itself. An animal 

 fed on a protein-free ration will soon starve to death, while 

 an animal receiving an insufficient amount will not make 

 a satisfactory development. 



It has already been stated that certain amino acids are 

 absolutely essential to life, while a certain amino acid is 

 essential only to growth. Thus not only must the ration 

 contain a sufficient amount of protein, but the protein 

 must contain those amino acids which are essential for 

 the maintenance and growth of the body tissues. It has 

 already been shown that the proteins may differ greatly 

 in their content of the different amino acids and, conse- 

 quently, that they may differ in nutritive value. Thus, 

 if a protein like zein of corn which is lacking in essential 

 amino acids is fed, it cannot be used for repair or growth 

 unless the missing amino acids are supplied in some other 

 protein. In an experiment with a man,^ it has been found 

 that the foUo^ving proteins ranked in the order named : 

 meat, milk, rice, potato, bean, bread, and corn. In recent 

 experiments by McCollum with pigs at the Wisconsin 

 Station,^ the following proteins ranked in the order named : 

 skim milk, casein, corn, wheat, oats, linseed meal, wheat 

 embryo. Thus, when feeds are used whose proteins contain 



1 "The Scientific Feeding of Animals," p. 04. 



2 Lusk, " Basis of Nutrition," p. 20. 



3 Jour, of Biol. Chem. XIX, 1914, p. 323. 



