Abstract: Using autumn-lambing ewes, this study investigated (i) the effects of diet on gonadotrophin secretion and responsiveness of the hypothalamic-pituitary-ovarian axis to exogenous GnRH during the early post-partum period; and (ii) whether ovulation prior to completion of uterine involution results in an increased incidence of aberrant ovarian cycles. Thirty-two ewes rearing 1.9±0.12 lambs were equally allocated to two dietary treatments at lambing (22 October ±0.2 day). Diets comprised ad libitum hay and 1.5 kg per ewe per day of one of two concentrates (11.5 MJ ME, 195 g CP per kg) containing 300 g kg?1 cracked maize grain (M) or 300 g kg?1 sugar beet pellets (S). Half of the ewes on each diet (G) received 25 i.v. injections of 250 ng GnRH in 2 ml 0.9% saline at 2 h intervals from days 12–14 post-partum while remaining ewes (N) were monitored for the resumption of spontaneous ovarian cyclicity. Blood samples were obtained from all ewes throughout the study (lambing to 18 December) for measurement of circulating hormone concentrations and the uteri and ovaries of all ewes were examined via laparoscopy on day 21 post-partum. There were no effects of dietary treatment on ewe daily live weight loss, lamb daily live weight gain or the immediate post-partum increase in circulating FSH concentrations. Diet did not affect insulin concentrations or LH pulse frequency on day 12 post-partum but LH pulse amplitude was lower in ewes fed concentrate M compared to concentrate S (1.4±0.10 versus 1.7±0.12 ng ml?1, respectively, P