The photorefractoriness in domestic goose: effect of gonads and thyroid on the development of postbreeding prolactinemia.

Blood samples were taken from adult male and female geese, and from gonadectomized (GX), thyroidectomized (TX) and gonadectomized+thyroidectomized (GX+TX) ones during the reproduction peak period (March 16), at the beginning of photorefractoriness (June 14), in the second half of the photorefractory period (August 14), and at the beginning of the postrefractory period (October 2). Surgeries were carried out at the age of 10-13 weeks. The birds were kept under natural light conditions. From the blood plasma prolactin (PRL), luteinizing hormone (LH), testosterone (T), progesterone (P4), 17 beta-oestradiol (E2) as well as thyroxine (T4) and triiodo-tironine (T3) were determined by RIA methods. At the beginning of photorefractoriness in intact geese the LH and E2 levels significantly decrease, relative to sexually active period, whereas the P4 remains at a high level. In ganders the LH shows only a slight decrease but the T level is significantly lower than in spring. The PRL, T4 and T3 levels increase after reproduction and give a peak value in both sexes. In both GX ganders and geese decreased T, P4 and T3 levels are observable and the PRL is decreased in females, and the LH is increased in both sexes. Gonadectomy does not influence the E2 in females, the PRL in males and the T4 in both sexes. In TX birds the PRL is higher in March and lower in June than the control level, but these changes are significant only in females. In TX females the P4 level is lower during reproduction and at the beginning of photorefractoriness. The T and E2 levels do not change during the photorefractoriness. In the second half of photorefractoriness a low PRL and P4 level, an increasing LH, T and medium high T4 and T3 levels characterized the intact male and female geese. In GX animals an increase of LH levels is occurred in both sexes. The T4 is higher in castrated-, and lower in ovarectomized geese. In TX birds the P4 is higher than in controls, but the difference is significant only in males. The levels of PRL, LH, T and E2 remain unchanged in TX animals. At the beginning of the postrefractory phase the T (in males) and the P4 and the T4 level increase in both sexes. The PRL and LH show a low value. In GX animals the high LH level refer to the increased sensitivity of hypothalamo-gonadotropic system, because of the absence of negative feed-back of sexual steroids.4+ in both sexes and a high thyroid hormone level and a transitional slight reactivation of gonadotropic-gonadal system occur then.