Plasma thyroxine and triiodothyronine levels after synchronization of estrus in the breeding season in ewes

Twenty nonpregnant cycling Tsigai ewes in the breeding season were treated for synchronization of estrus using intravaginal progestagen sponges (medroxyprogesterone-acetate, MAP) followed by an intramuscular injection of 350-400 IU of pregnant mare serum gonadotrophin (PMSG). A control group of ewes was formed from 20 animals in the natural estrous cycle. Hormonal status was investigated by determination of plasma triiodothyronine (T-3) and thyroxine (T-4) concentrations using radioimmunoassay (RIA). Samples of jugular venous plasma were collected on the day of sponge insertion (P), the day of estrus (0, day), 7, 14 and 18 days after estrus. Plasma T-3 levels in the control group of ewes were significantly lower compared to the ewes after synchronization of estrus, except the level of T3 on day 18 after estrus. Plasma T-4 level was not significantly different in the treated and control ewes, except on day 18 after estrus.