No abstract

No abstract

No abstract

The involvement of the thyroid gland in the response of young chickens to heat stress was studied. Mean survival times when exposed to 50 C were significantly shorter for 3-week-old broiler male chickens injected with 40 micrograms L-thyroxine (T4)/100 g body weight compared to chickens injected with 30, 20, or 0 microgram of T4/100 g body weight. A significant reduction in heat stress survival time was obtained when T4 was injected 12, 18, or 24 hr before heat stress but not 6 hr before. Triiodothyronine (T3) reduced heat stress survival time when administered 12 to 24 hr before the stress but not when given 6 hr before. Chickens made hypothyroid by radiothyroidectomy had significantly longer heat stress survival times than controls. Likewise, chickens fed a diet containing .2% thiouracil 10 days before heat stress at 28 days had significantly longer survival times than control birds.

No abstract