Metabolic responses of the rooster after exogenous thyroid hormones

Total sensible heat loss, O2 consumption, and CO2 production were monitored in 20 White Leghorn roosters (1.85 +/- .05 kg body weight) subjected to either saline, or triiodothyronine (20 micrograms/kg; T3), or thyroxine (50 micrograms/kg; T4) administered in a single dose. Treatment occurred after a 26-hr fast and the fast was maintained for the duration of the experiment. Plasma T3 concentrations in birds treated with T3 were higher than controls for an 8-hr period after treatment (P less than .01). Plasma T4 in birds treated with T4 was higher than controls for the 24-hr sampling period (P less than .01). Sensible heat loss, but not O2 consumption or CO2 production, was affected by treatment during the first 10 hr following treatment (P less than .05). Heat loss after T3 and T4 treatments did not differ; however, pooled results of the treated groups were higher than that of control (P less than .05). Heat loss, O2, and Co2 varied with time (P less than .001) during the 10-hr period following treatment or saline. Sensible heat loss was also affected by treatment during the period of 21 to 25-hr posttreatment (P less than .001). During that period, the heat loss after T4 treatment was greater than that after T3 (P less than .005). These data suggest that a single administration of either T3 or T4 can affect total sensible heat loss but not O2 consumption of CO2 production within 10-hr posttreatment in mature roosters.