PHYSIOLOGICAL EFFECT ON GROWTH AND REPRO- 

 DUCTION OF RATIONS BALANCED FROM RESTRICTED 

 SOURCES 



By E. B. Hart, E. V. McCollum, and H. Steenbock, of the Department of Agricultural 

 Chemistry, and G. C. Humphrey, of the Department of Animal Husbandry, Wisconsin 

 Agricultural Experiment Station 



Our early work (6)^ on the nutrition of Herbivora with restricted 

 rations demonstrated clearly the inadequacy of the accepted theory as 

 to what constitutes a balanced or complete ration. Up to that time 

 total protein (without reference to quality), energy, and ash materials 

 were considered the essentials of a ration. The latter, however, occu- 

 pied no position in the mathematical expression of the standards devel- 

 oped. The standards have been stated only in terms of total digestible 

 protein and energy. It is, however, probably true that in a practical 

 sense and with the generally accepted knowledge of the quality of feeding 

 materials accumulated from a long and varied experience, such standards 

 have had and will continue to have very great value; but their limita- 

 tions are also made evident by this earlier work and are emphasized by 

 what we have since done. Within the past few years our knowledge 

 (i, 2, 7, 9, ID, 13, 16, 17) of the essentials of a ration have expanded, and 

 to-day we would consider a ration complete and efficient only when it 

 contained protein of adequate quantity and quality, adequate energy, 

 ash materials in proper quantity and proportion, and two factors of 

 unknown constitution (vitamines), designated by this laboratory (11) 

 "fat-soluble A" and "water-soluble B." 



In addition to the above normal factors, there may be introduced 

 with natural foodstuffs the important factor of toxicity (4, 5, 12). This 

 can be wholly absent or so mild in its effects as to be entirely obscured 

 when the other essentials of a ration are at an optimum adjustment; 

 or with fair adjustment it may only reveal its effects when the ration is 

 continued over a very long time and the animal involved in the extra 

 strains of reproduction and milk secretion. This resistance to toxicity 

 is very materially increased through a proper adjustment of the normal 

 factors of nutrition. 



With this recognition of all the normal factors for adequate nutrition 

 there should not arise simultaneously a desire for a mathematical expres- 

 sion of these factors in feeding standards. It is doubtful if this can ever 

 be done, at least for certain of them. For example, the role of the 

 mineral nutrients is so varied, including such widely separated functions 



' Reference is made by number to " Literature cited," p. 197-198. 



Journal of Agricultural Research, Vol. X. No. 4 



Washington, D. C. ^ ^ July 23, 1917 



. (175) KeyNo. Wis.— 7 



