Studies of pituitary function in lactating ewes

Abstract

The release of LH from the pituitary of lactating ewes was studied. In Exp. 1, ewes were injected with 50 microng oestradiol benzoate (OB), 2-0 mg testosterone propionate (TP) or oil only (control) on days 5, 10, or 20 after lambing. LH was measured in peripheral plasma samples obtained 20-38 h after treatment, and the ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between Day 5 and 20 after OB treatment but increased after TP treatment. The releases of LH were not always accompanied by ovulation and the incidence of ovulation was higher in ewes treated with TP. In Exp. 2, lactating ewes were injected with 1 or 5 (at 2-h intervals) doses of 50 microng Gn-RH, on Days 12 or 25 after lambing. LH was measured in peripheral plasma samples collected every 2 h for 10 h and every 3 h for a further 70 h. Release of LH occurred in all ewes, the amount being greater in ewes receiving multiple injections and in ewes treated on Day 25. The incidence of ovulation was higher after treatment on Day 25. Multiple injections of Gn-RH appeared to reduce the incidence of abnormal corpora lutea.

Successful pregnancies after transfer of embryos recovered from ewes induced to ovulate 24-29 days post partum

“…1). This provides us with evidence to question the suggestion (Restall et al, 1977;McNeiUy et al, 1982;Wright et al, 1983) that inadequate corpora lutea arise from ovulation of inadequately gonadotrophin-primed follicles which in turn are incapable of producing normal oocytes. In the final analysis the developmental competence of the sheep oocyte is assessed by its ability to undergo fertilization and subsequent embryonic development.…”

Effects of a Single Injection of LHRH on the Response of Anestrous Ewes to the Introduction of Rams1

“…One-half of the ewes in each group received an im injection of 50 ~tg of LHRH (Sigma L0507) 4 in saline on the day that the males were introduced. This dose of LHRH was reported to induce a normal release of LH in lactating ewes (Restall et al, 1977). Rams remained with the ewes for 30 d, after which the ewes were transferred to regular breeding flocks with rams at a ratio of one/40 ewes.…”

Reproduction in the Sheep and Goat

“…After parturition there is a period of ovarian quiescence, and the return to cyclical activity depends princi pally on the season and, to a much lesser ex tent, lactation. Nutrition and season have been shown to interact with lactation in determin ing the postpartum interval to first estrus (Corbett and Furnival, 1976;Restall and Starr, 1977). Breeds that experience anestrus and lamb or kid, as they normally do in the anestrous period, do not begin cyclical activity until the following season, but this should not be confused with lactational anestrus.…”