Some effects of thyroidectomy on growth, heat production and the thermoregulatory ability of the immature fowl ( Gallus domesticus)

Abstract

1. 1.|The effect of thyroidectomy at 12 days of age on weight gain, and on heat production and thermoregulatory ability of 4- to 5-week-old chickens at temperatures within and below the thermo-neutral zone was investigated. 2. 2.|Despit the absence of thyroid tissue, as demonstrated with radioiodine, a small amount of thyroxine was found in the plasma of some thyroidectomized (TX) birds. 3. 3.|Thyroidectomy depressed weight gain; pair-fed controls grew significantly faster than TX birds. 4. 4.|Resting heat production of TX birds at thermoneutrality (30°C) was depressed by 18% ( P < 0.001) and body temperature by 0.4°C ( P < 0.001). 5. 5.|At 12°C heat production of TX birds was similar to that of controls but the body temperature of TX birds was 0.7°C lower ( P < 0.001). 6. 6.|Thyroidectomized birds were unable to regulate body temperature at 5°C even if thyroxine was provided on the day before and at the time of cold-exposure. This inability to thermoregulate was probably due to inadequate insulation and poor nutritional status.