Studies on Zinc Deficiency in the Chick

Abstract

During a 14-day experimental period (from 12 to 26 days of age) the growth of chicks fed a semipurified diet containing soybean protein was significantly increased by addition of zinc to the diet. However, added zinc had no effect on the growth of chicks which received a similar diet containing casein and gelatin as the protein sources. Both diets contained approximately 30 p.p.m. of zinc, 4.8 p.p.m. of which was supplied in the mineral mixture. Chicks which received the soybean protein diet with zinc omitted from the mineral mixture exhibited markedly retarded growth, lowered efficiency of feed utilization and shortened and thickened tibiotarsae. Zinc deficiency had no apparent effect on the percentage of ash in the tibiotarsae or on liver or carcass composition. Omission of zinc from the mineral mixture in the casein-gelatin diet also depressed growth, although the growth depression was not as great as that observed with the soybean protein diet. The addition of excess calcium to the soybean protein diet depressed weight gain and feed efficiency. Additional zinc, however, counteracted these effects, suggesting that excess calcium may increase the dietary requirement for zinc. The possible relationship of the above findings to unidentified chick growth factors is discussed.