Studies on the Soy and Fish Solubles Growth Factors for Chicks

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Abstract
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. 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. 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. 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.