THE EFFECTS OF LONG-ACTING OXYTOCIN, GNRH AND FSH ADMINISTRATION ON THYROXINE, TRIIODOTHYRONIN, ESTRADIOL-17-BETA AND PROGESTERONE LEVELS AS WELL AS CONCEPTION RATES IN POSTPARTUM EWES

This work was a first attempt to discover whether the suppression of a denopituitary gonadotropin secretion might be responsible for a decrea se of systemic T-4 and T-3 levels in the post-partum period in ewes, a nd also whether the depression of T-4 and T-3 levels might be retroact ively responsible for a depression of sexual activity in the post-part um period and in spring. T-4, T-3, E(2) and P-4 levels were observed i n four groups of ewes. After parturition (lambings took place in the f irst 10 days of February) the animals were treated with an oxytocin-ba sed preparation (/2-0-methyltyrosin/deamino-1-carba-oxytocinum, Depoto cin injection, Leciva), synthetic LH-RH (Dirigestran injection, Spofa) or pituitary gonadotropin FSH (Folicotropin injection, Spofa). Group 1 was the control group (n=10), and each animal received 2 mi saline. The ewes in Group 2 (experimental; n=9) were treated with 0.14 mg Depo tocin per animal, the ewes in Group 3 (experimental; n=10) were given 200 mu g Dirigestran per animal, and the ewes in Group 4 (experimental ; n=5) received 160 IU Folicotropin. All preparations were administere d in two doses: an intramuscular dose at 24 h post-partum and a subcut aneous dose at 72 h post-partum. On Day 51, oestrus was induced in all animals by combined Agelin (6-chloro-6-dehydro-16methylene-17 alpha-h ydroxyprogesterone) and PMSG treatment. Blood samples were obtained fr om the jugular vein at 24 h ante-partum (a.p.) (Day-1), at 36 h post-p artum and on Days 4, 7, 14, 17, 21, 25, 34, 42 and 51 post-partum. Whe n compared with the controls, altered T-4 and T-3 dynamics and signifi cantly increased levels of T-3 (between Days 4 and 25, P < 0.05, P < 0 .01, except for Days 7 and 14), E(2) (at 36 h, P < 0.05, and on Days 4 , P < 0.05, and 25, P < 0.05) and P-4 (at 36 h) were observed in the D epotocin-treated animals. In this group, conception rates and births w ere increased by 44.5% and 111.1%, respectively. Altered T-4 and T-3 d ynamics significantly increased levels of T-4 (Day 21, P < 0.01), T-3 (between 36 h and Day 25, P < 0.05, P < 0.01, P < 0.001), E(2) (betwee n 36 h and Day 34, P < 0.05, P < 0.01, P < 0.001, except for Days 7 an d 17) and P-4 (at 36 h) were recorded in the Dirigestran-treated ewes in which conception rates and births were increased by 22.2% and 33.4% , respectively. In the Folicotropin-treated group, T-3 levels were sig nificantly increased (between Days-1 and 21, P < 0.05, P < 0.01, P < 0 .001, except for Day 14 post-partum). In these animals, conception rat es and births were increased by 4.5% and 13.4%, respectively. On the b asis of the above results, we suggest that the causes of depression of T-4 and T-3 levels after parturition in spring might be a lack of gon adotropins. Decreased T-4 and T-3 secretion in certain phases of the p ost-partum period might be retroactively responsible for the decline i n post-partum sexual activity in ewes.