Restricted feed intake influences thyroid hormone production and peripheral deiodination in chickens

Thyroid hormones are of major importance in determining metabolic state both in mammals and in birds. Whether or not feed intake itself has an autoregulatory role in adjusting the setpoint of thyroid hormone activity is yet not well understood. The present work investigates the effects of restricted feed intake on the serum levels and on the peripheral metabolism of thyroid hormones. Also, the sensitivity of the pituitary-thyroid axis was looked at by means of thyrotropin releasing hormone provocation test. Several groups of Hunniahybrid chickens aged 2-6 weeks were used. Restriction was made by providing the experimental animals 70 and 85 percent of the amount of food consumed in the ad libitum fed control group. It was found that feed restriction lowers circulating concentration of triiodothyronine probably by inhibiting the activity of liver deiodinase and also decreases the sensitivity of the pituitary-thyroid axis meaning that both central and peripheral regulatory mechanisms of thyroid economy are affected by feed restriction.