Dietary protein effects on the broiler's adaptation to triiodothyronine

The purpose of this experiment was to study the effects of dietary protein on metabolic adaptations in birds given triiodothyronine (T-3) at 28 d of a ge. Knowledge about the role of dietary protein in thyroid metabolism is la cking. Male broiler chickens were fed diets containing either 120 or 300 g crude protein/kg from 7 to 28 d. At this time, one-half of each group was g iven that diet supplemented with I mg/ kg TS Birds were sampled at 0, 2, 5, 7, 9 and 12 d following the initiation of the Ts treatments. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and fe ed consumption, hepatic enzyme activities and plasma thyroid hormones and m etabolites. As expected, IVL was greater at 28 d in birds fed the lower lev el of protein. Moreover, when T-3 was added to either diet, IVL decreased b y 50% after 5 d. Plasma IGF-I and T-4 were greater while T-3 and GH were le ss when birds were fed the higher level of crude protein. Plasma T-3 increa sed and T-4 decreased 3 d following the addition of T-3 to diets containing either level of crude protein. Most metabolic changes in response to feedi ng T-3 occurred within 2 to 5 d, suggesting that changes in intermediary me tabolism preceded morphological changes that we have previously seen. In ad dition, dietary protein levels may not affect adaptive responses to T-3.