Energy and protein relations in the broiler. 5. Lipogenesis, glucose production and metabolic hormone levels as functions of age and dietary protein levels.

Both a decrease in the dietary carbohydrate level and an increase in the protein level decrease lipogenesis in chicks. Interpreting results of previous experiments can be confounded by alterations in the quantity of carbohydrate because as protein was added to the diets used in these studies, carbohydrate was decreased. In the present study, diets containing 13, 16, 19 or 23% protein and 70% carbohydrate calories were fed to Ross male chicks from 1 to 4 weeks of age to determine the effect of dietary protein level (% crude protein) on growth and intermediary metabolism in 2, 3, and 4-wk old chicks. All treatment groups were limited to that amount of feed consumed by the 23% protein group. There were no significant differences in body weights among the treatment groups at 4 wk of age. An increase in dietary protein (23 vs. 13%) increased (P less than 0.05) in vitro glucose production by liver slices from 4-wk old chicks. In contrast, the same increase in dietary protein decreased (P less than 0.05) in vitro lipogenesis by liver slices from 2, 3, and 4-wk old chicks. The same increase in dietary protein increased (P less than 0.05) both insulin (INS) and thyroxine (T4) and decreased (P less than 0.05) triiodothyronine (T3). Serum T3 and T4 concentrations were less (P less than 0.05) and INS concentrations were greater (P less than 0.05) in 4-wk old chicks compared to 2-wk old chicks.