FORBES: MINERAL ELEMENTS IN NUTRITION 437 



We shall now consider the results of mineral metabolism studies 

 with swine. This subject is of especial importance in this con- 

 nection because no other animals are so grievously sinned against 

 in the provision of their mineral requirements. Several fac- 

 tors unite in bringing about this state of affairs. Among these 

 are the extreme rapidity of growth of improved hogs, the great 

 weight of fat carried, the early age at which reproduction and 

 lactation occur, the custom of rearing hogs in comparatively 

 close confinement, and the feeding of too little else than corn. 

 This combination of conditions often results in the crippling of 

 hogs during shipment to market, the breaking down of sows 

 while suckling pigs, and a general abbreviation of the period 

 of usefulness of breeding stock. 



Our studies with swine have been on the specific effects of 

 corn and of supplements to corn, and a comparison of the nu- 

 tritive values of several pure compounds of phosphorus, these 

 studies having been conducted by feeding, slaughter, and car- 

 cass analysis experiments, and by metabolism investigations. 



In these feeding and carcass analysis experiments the specific 

 effects of corn as an only food for growing swine were shown 

 to be, in general, a retarded development of proteid and bony 

 tissues and an over-development of fatty tissue. This results 

 in the production of fine-boned, poorly muscled, undersized, 

 and over-fat animals, which reach their limit of growth pre- 

 maturely and which are characterized by less than normal breed- 

 ing capacity. Impaired fecundity seems to result from dis- 

 couragement of proteid increase generally and from the lessened 

 circulation of blood in the female reproductive organs, this 

 last being caused b}^ pressure of the excessive amounts of internal 

 fat which accumulate about these parts. With hogs fed on 

 corn alone, the bones, muscles, liver, kidneys, lungs, heart, and 

 spleen all compose an abnormally small proportion of the in- 

 crease in weight, and fat composes an abnormally large part of 

 the increase. The bones are lacking both in density, as indi- 

 cated by ash content, and in breaking strength. 



Many of the specific effects of corn as an only food for grow- 

 ing- animals are due to its insufficient content of protein and to 



