CARRY-OVER EFFECTS OF DIETARY CRUDE PROTEIN AND TRIIODOTHYRONINE (T-3) IN BROILER-CHICKENS

Indian River male broiler chickens growing from 7 to 30 d of age were fed on diets containing crude protein levels ranging from 120 to 300 g /kg plus 0 or 1 mg triiodothyronine (T-3/kg diet, The purpose of this study was to examine the effects of these treatments on lipogenesis af ter a common diet was fed (180 g crude protein/kg diet from 30 to 56 d of age), Dietary treatment groups were sampled at 30 and 56 d. In vit ro lipogenesis was determined by incubating liver explants for 2 h at 37 degrees in Hanks' salts containing 25 mM-HEPES and 10 mM-[2-C-14]ac etate and then measuring acetate incorporation into total lipid. Growt h and feed consumption from 7 to 30 d increased (P < 0.01) as dietary protein increased from 120 to 210 g/kg diet, Both measurements decreas ed as crude protein increased from 210 to 300 g/kg diet. T-3 decreased (P < 0.01) growth and feed intake during this period. Low-protein (< 180 g/kg) diets increased (P < 0.05) and T-3 decreased lipogenesis in 30-d-old chickens. Although birds given T-3 from 7 to 30 d grew at the greatest rate from 30 to 56 d of age, the final body weight was still less than controls. In vitro lipogenesis at 56 d of age was not affec ted by either of the two dietary treatments, In contrast, the relative size of the abdominal fat pad (g/kg body weight) at 56 d was decrease d by feeding T-3 from 7 to 30 d, Any changes in metabolism elicited by either dietary protein levels or hormone treatments may be specific t o the particular dosing interval and are not sustained when a common d iet is fed during a repletion period.