The effects of long-acting oxytocin, GnRH and FSH administration on thyroxin, triiodothyronin, oestradiol 17-β and progesterone levels as well as conception rates in post-partum ewes

Abstract

Abstract This work was a first attempt to discover whether the suppression of adenopituitary gonadotropin secretion might be responsible for a decrease of systemic T4 and T3 levels in the post-partum period in ewes, and also whether the depression of T4 and T3 levels might be retroactively responsible for a depression of sexual activity in the post-partum period and in spring. T4, T3, E2 and P4 levels were observed in four groups of ewes. After parturition (lambings took place in the first 10 days of February) the animals were treated with an oxytocin-based preparation (/2-0-methyltyrosin/deamino-1-carba-oxytocinum, Depotocin 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 ml saline. The ewes in Group 2 (experimental; n = 9) were treated with 0.14 mg Depotocin per animal, the ewes in Group 3 (experimental; n = 10) were given 200 μg Dirigestran per animal, and the ewes in Group 4 (experimental; n = 5) received 160 IU Folicotropin. All preparations were administered in two doses: an intramuscular dose at 24 h post-partum and a subcutaneous dose at 72 h post-partum. On Day 51, oestrus was induced in all animals by combined Agelin (6-chloro-6-dehydro-16 methylene-17 α-hydroxyprogesterone) and PMSG treatment. Blood samples were obtained from the jugular vein at 24 h ante-partum (a.p.) (Day -1), at 36 h post-partum and on Days 4, 7, 14, 17, 21, 25, 34, 42 and 51 post-partum. When compared with the controls, altered T4 and T3 dynamics and significantly increased levels of T3 (between Days 4 and 25, P