The Seasonal Response of Chicks to an Unidentified Growth Factor Found in Forage Juice

IN A recent paper (Kohler and Graham, 1951) evidence was presented which showed that the juice of forage crops contains an unidentified chick growth factor. The growth promoting effect of the juice preparations could be demonstrated when all known vitamins and crude sources of A.P.F. were included in the basal rations. The growth factor is presumably the same as that described by Scott (1951) for turkeys and may be related to the “grass juice factor” for rats and guinea pigs described by Kohler, Elvehjem and Hart (1938). At various times it has been noted that responsiveness of the chicks to the growth factor varied considerably. Indeed, at times we “lost” the response entirely. Chicks used in these studies have been purchased from local hatcheries. During the past several years, assays have been set up at intervals of 1 to 2 weeks. Since positive and negative controls have been included in . . .