Submitted to: Poultry Science
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2004
Publication Date: June 1, 2004
Citation: Rosebrough, R.W., Poch, S.M., Russell, B.A., Richards, M.P. 2004. Time course of thyroid hormone replacement and lipogenic enzyme gene expression in broilers [abstract]. Poultry Science. 83 (Suppl. 1):114. Technical Abstract: The purpose of this experiment was to determine the possible relationship between certain indices of lipid metabolism and specific gene expression in chickens fed methimazole to produce a kind of artificial hypothyroidism. Male, broiler chickens growing from 7 to 28 days of age were fed diets containing 18% crude protein and either 0 or 1 g methimazole per kg of diet. At 28 days, these two groups were further subdivided into groups receiving 18% crude protein diets containing either 0 or 1 mg triiodothyronine (T3) per kg. Birds were sampled from at 28, 30 and 33 days. Measurements taken included in vitro lipogenesis (IVL), malic enzyme (ME) activity the expression of the genes for ME, fatty acid synthase (FAS) and acetyl coenzyme carboxylase (ACC). Hypothyroidism decreased IVL and ME at 28 d of age; however, T3 supplementation for 2 d restored both IVL and ME. Paradoxically, continuing T3 replenishment for an additional 3d decreased IVL without affecting ME activity. In contrast, supplemental T3 decreased IVL in euthyroid birds, regardless of the dosing interval, but had no effect on ME activity. Methimazole decreased plasma T3, T4, and uric acid. Although methimazole decreased ME gene expression, there was only a transitory relationship between enzyme activity and gene expression when plasma T3 was replenished with exogenous T3. These data may help to explain some of the apparent reported dichotomies in lipid metabolism elicited by changes in the thyroid state of animals. In addition, most metabolic changes in response to feeding T3 occurred within 2 to 5 d, suggesting that changes in intermediary metabolism preceded morphological changes. In conclusion, the thyroid state of the animal will determine responses to exogenous T3.