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Prevention of Coprophagy in the Rat and the Growth-stimulating Effects of Methionine, Cystine and Penicillin when Added to Diets Containing Unheated Soybeans¹

Graduate School of Nutrition, Cornell University, Ithaca, New York

The growth inhibition caused by feeding unheated soybeans to rats is partially overcome by supplementing the diet with methionine, cystine or penicillin. With conventional rats these supplements were effective when the diet contained either a large quantity (50%) of unheated, solvent-extracted soybean flakes or a small quantity (25%). When coprophagy was prevented completely by the use of fecal collection cups attached to the tail, the beneficial effect of penicillin was abolished at either level of unheated soybean in the diet. The beneficial effect of methionine was abolished by preventing coprophagy when the higher level of soybean flakes was fed, but not with the lower (25%) level. Prevention of coprophagy did not affect cystine-supplementing effects at either level of soybean in the diet. The results are interpreted to mean that a biologically active substance is excreted in the feces as a result of feeding an antibiotic and this substance exerts its beneficial effect only after ingestion of feces and thus cycling the substance to the upper part of the intestinal tract. It was concluded that this substance cannot be cystine, although fecal cystine undoubtedly contributes under these conditions. Cystine utilization is not impaired in the coprophagy-prevented rat, but some alteration in the metabolism of methionine is believed to be caused by the prevention of coprophagy.

Manuscript received 25 August 1964.