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Studies on the Soy and Fish Solubles Growth Factors for Chicks¹

Department of Biochemistry, State University of New York, Upstate Medical Center, Syracuse, New York

1. A 20% casein plus 10% gelatin diet was deficient in methionine for chick growth. When supplemented with a mixture of all the essential amino acids or all the amino acids in 20% soy protein, it was still deficient in two unidentified factors: the "soy" and the "fish solubles" factors. Both factors were required in the diet simultaneously to obtain the best growth response from either.

2. A 20% casein plus 10% gelatin plus 0.6% methionine plus 20% fish solubles diet provided a suitable basal diet for detecting the soy factor. It was adequate in protein, contained an excess of the fish solubles factor, and allowed a maximal growth rate when supplemented with soy protein. The growth stimulation produced by the addition of 20% of soy protein to this diet could not be duplicated by any amino acid or by a mixture of the amino acids in 20% soy protein. Egg yolk, lactalbumin and liver residue were also good sources of the soy factor.

3. A 35% soy protein diet supplemented with 0.75% of methionine and 0.4% of glycine provided a suitable basal diet for detecting the fish solubles factor. This diet contained adequate protein and soy factor, and it allowed a maximal growth rate of chicks when supplemented with 10 or 20% of fish solubles. Fermentation residue, distiller's solubles, and egg yolk were also good sources of the fish solubles factors.

4. Soy protein exerted a protective effect in thyrotoxic chicks. Fish solubles had little protective effect by itself and largely nullified the beneficial effect of soy protein when fed together with the latter.

Manuscript received 18 December 1961.