Dietary fat and triiodothyronine (T3) interactions in the broiler chicken

Male, Indian River, broiler chickens growing from 7 to 28 d were fed on diets containing 180 g crude protein, 300, 600 or 1200 kcal fat calories and 0 or 1 mg T3/kg diet. Birds were bled and sacrificed at d 28, 29 and 30. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption and hepatic enzyme activities. Plasma metabolites as well as thyroid hormones were also determined. Dietary fat levels did not influence growth or feed intake. In contrast, T3 decreased growth and feed intake by 25% without altering the efficiency of feed utilization. Dietary T3 and additional fat decreased IVL and lipogenic enzyme activities. Dietary T3 increased plasma T3 and decreased plasma T4. Dietary fat energy levels had no effect upon plasma thyroid hormone levels. Although both additional dietary fat and T3 modify broiler lipid metabolism, there was no additional treatment effect when high-fat diets were supplemented with T3. In contrast to previous reports, T3 did not increase any parameter associated with lipid metabolism.