Effects of Dietary Protein Restriction on Circulating Concentrations of Growth Hormone in Growing Domestic Fowl (Gallus domesticus)

Two- to three-week-old broiler chicks were fed isocaloric purified diets with varying levels of protein (soy protein supplemented with glycine and methionine). The growth rates of the birds were monitored throughout the period of 14 days on the purified diets, while the circulating concentrations of growth hormone (GH) were determined at the end of this period. As expected, decreases in the dietary protein level were associated with concomitant reductions in growth rate. While this decrease in growth rate was observed with chicks fed 12 and 18% protein (compared with 24%), circulating concentrations of GH were observed to be only elevated with severe protein restriction (10% and lower). There was also evidence for some progressive increase in plasma concentrations of GH as dietary protein levels were decreased.