EFFECT OF CGNRH-I ON THE PLASMA THYROID-HORMONES LEVEL IN THE DOMESTIC HEN DURING GROWTH SAND SEXUAL-MATURATION

The effect of chicken GnRH-I on plasma level of thyroid hormones (T-4 and T-3) was investigated in chicken during last phase of sexual matur ation and the initial period of egg-laying. Synthetic cGnRH-I Tvas inj ected at 15 week of pullers age at doses 35 mu g/bird or 20 mu g/bird for 3 or 5 consecutive days, respectively. The injections were carried out at 09:00 hr every day. Blood samples were collected at 16, 18, 20 and 22 week of age, and T-4 and T-3 were measured by RIA methods. Dur ing sexual maturation in chicken a gradual decrease in plasma T-4 and T-3 concentrations was observed during sexual maturation in chickens. Both doses of cGnRH-I advanced the onset of egg-laying by few days, in creased the initial eggs production, and significantly decreased T-4 a nd T-3 plasma levels at 16, 18 and 20, and 16 and 20 week of age, resp ectively. Results obtained demonstrate that cGnRH-I injected at 15 wee k of chicken age nor. only advanced sexual maturation but also affecte d concentration of blood thyroid hormones. It may be concluded that in jections of cGnRH-I to immature chicken modify the activity of the hyp othalamo-pituitary-thyroid axis.