Some effects of epidermal growth factor at three stages of pregnancy in Merino ewes

Abstract

Pregnant Merino ewes were treated with 90 8g murine epidermal growth factor (EGF) per kg body weight at either 25 (n = 80), 50 (n= 40) or 75 (n =40) days of gestation. Untreated control ewes were included at each gestational age (n=20, 12 and 12 respectively). Fifteen and twenty per cent of the ewes treated with EGF at days 25 and 50 respectively failed to lamb, significantly more (P < 0.01 ) than in ewes treated at day 75, where only one ewe failed to lamb, and in control ewes which all lambed. These differences were not reflected in significant differences between the overall percentage of lambs born in each group, as the incidence of abortion in single-bearing ewes was higher than in ewes carrying multiple fetuses. All lambs born alive to EGF-treated ewes appeared normal. Plasma progesterone concentrations measured before treatment and at 8, 24 and 48 h after EGF injection fell significantly in treated ewes relative to controls (P<0.01 at day 25; P<0.05 at days 50 and 75) and concentrations were lowest at 8 and 24 h after injection in those ewes which aborted. Following EGF treatment at days 25 and 50 of gestation, abortion occurred in all ewes with very low plasma progesterone concentrations 8 to 48 h after EGF injection, probably as a result of EGF-induced luteolysis. In other ewes plasma progesterone concentrations returned to pretreatment values by 48 h, indicating incomplete luteolysis. The delayed abortion observed in some of these ewes further suggests that other mechanisms of action are involved in EGF-induced abortion.