Effect of thyroxine and thiouracil additions to diets containing rapeseed meal, on chick growth and carcass composition

Experiments have been conducted to study the hypothyrotic status of chicks fed rapeseed meal. Protamone supplementation did not correct growth depression due to feeding rapeseed meal although inclusion levels up to 0.1% may have induced a hyperthyrotic condition which in itself leads to a growth depressing effect. Changes in liver and carcass composition were observed when diets containing rapeseed and soybean meal were supplemented with protamone and thiouracil. It is concluded that although birds fed rapeseed meal are abnormal with respect to thyroid metabolism, it is likely that factors other than a simple reduction in serum thyroxine concentration are responsible for the growth depression observed for such birds.