INTRODUCTION 



THE problems of nutrition concern the farmer both directly 

 and indirectly - indirectly because his function in society is to 

 furnish the materials for the nutrition of man ; directly, because 

 an essential part of that function consists in the economical 

 conversion of vegetable into animal products by means of farm 

 animals. Particularly is this true regarding the inedible prod- 

 ucts of the farm. It is a well-recognized fact that only the 

 smaller portion of the solar energy or of the proteins which are 

 stored up in the farmer's crops is directly available for man's 

 use. Even in distinctively food crops, such as wheat, for ex- 

 ample, more than two-thirds of the energy which they contain 

 may be unavailable for human nutrition, while the grasses and 

 legumes, so important in all systems of agriculture, are of no 

 direct value as food for man. The essential function of the 

 animal in a permanent system of agriculture is the conversion 

 of as large a proportion as possible of these inedible products 

 into forms whose matter and energy can be utilized by the 

 human body. It is true that animal products contribute largely 

 to our supply of clothing and also that, as a motor, the work 

 animal plays an important part in agriculture and industry. In 

 both respects, however, substitution is possible to a greater or 

 less extent. Vegetable fibers may to a degree replace animal 

 fibers in our textiles, while inanimate motors seem destined to 

 fill an increasing role in power production in all its aspects. 

 But for the conversion of the by-products of the farm and fac- 

 tory into human food, there is as yet no suggestion of an agency 

 which can take the place of the animal body. 



With the growth of the non-agricultural population it is in- 

 creasingly important that this function of conserving the food 

 supply through the utilization of inedible soil products shall be 

 performed with a maximum of efficiency. This requires, on the 

 one hand, as intimate a knowledge as possible of the funda- 

 mental laws governing the nutrition of farm animals, so that 



