Ovarian stimulation following repeated injections of LH or LH + FSH in Ile-de-France sheep in early and mid-seasonal anoestrus

Abstract

Ile-de-France ewes were treated either 32 ± 9 days (early anoestrus, n = 12) or 80 ± 10 days (mid-anoestrus, n = 8) after the beginning of seasonal anoestrus (4 April ± 14 days). At each treatment time all animals received intravenous injections of 10 μg ovarian luteinising hormone (oLH) every 2 h for 48 h. In addition to the oLH injections, half the animals from each group received 50 μg ovarian follicle-stimulating hormone (oFSH) every 2 h for the first 24 h of treatment. Jugular and ovarian venous blood samples were taken every 20 or 60 min on the day preceding the commencement of treatment and throughout the entire treatment period. The plasma concentrations of luteinising hormone (LH), follicle-stimulating hormone (FSH) and oestradiol-17β (E 217β) were determined in these samples using radioimmunoassays. Jugular blood samples were taken daily for 15 days after the last injection in order to study the pattern of progesterone secretion. Follicular populations were studied in 12 ewes at three different times: early anoestrus ( n = 4), mid-anoestrus ( n = 4) and at resumption of cyclicity ( n = 4). The number of LH pulses observed in ewes prior to the commencement of treatment on Days 32 and 80 was 0.73 ± 0.9 pulses 6 h −1 and 0.75 ± 0.5 pulses 6 h −1, respectively. Mean FSH levels prior to treatment on Days 32 and 80 were 3.7 ± 0.49 ng ml −1 and 2.6 ± 0.19 ng ml −1 ( P < 0.001), respectively. In ewes treated with LH only six out of six of the ewes in early anoestrus ovulated compared with only one out of four ewes in mid-anoestrus. All the ewes receiving the combined LH and FSH treatment ovulated, regardless of the stage of anoestrus. Of all the ewes that ovulated, short luteal phases were observed in two out of seven and one out of ten ewes receiving the LH and the combined LH-FSH treatment, respectively. During mid-anoestrus significant decreases in the total number of follicles in class C1 (170–863 μm) and class C2 (863–3569 μm) were observed and there were fewer normal follicles in both classes ( P < 0.05). We distinguished two types of anoestrus: (1) a slight anoestrus characterised by high FSH plasma levels and presence of normal follicles. In this case, ovulation was induced by repeated injections of LH only; (2) a deep anoestrus characterised by low FSH plasma levels and a severe reduction of the total number of antral follicles. In this case, the induction of ovulation required LH and FSH.