Influence of Thiouracil on Chickens Selected for High and Low Body Weights

ALTHOUGH experiments have been conducted in which lines were selected for specific characteristics little is known about the physiological mechanisms through which the genes are expressed in causing changes in the selected trait. To study differences in growth rates of lines which have been selected in divergent directions for body weight, one might impair the secretion of the thyroid hormones and observe the ensuing effects on growth since these hormones are implicated in growth processes (Pitt-Rivers and Tata, 1959; Kamar, 1961). The present experiment was designed to provide information on the effect of feeding a ration containing thiouracil to male and female chickens from lines which had been subjected to mass selection in opposite directions for body weight. Several characteristics were measured to ascertain physiological differences in these lines and differences in their response to the feeding of a ration containing thiouracil. Differences in blood pressure were of major concern …