Control of ovarian follicles activity in the ewe.

During the ovine estrous cycles, three waves of follicular growth, closely associated with the FSH secretion pattern, were observed. The parameters of these follicular waves and the ability of follicles to produce steroids in vitro were studied in various conditions. In vivo, the follicular events were similar between the breeding season and the anestrus, except for the lack of ovulation; but at the end of the breeding season and in anestrus, the follicles lose a big part of their aromatization ability. In ewes carrying the Booroola fecundity gene or Cambridge fecundity gene, the reduction in follicular atresia seems to be one of the main follicular features implicated in the control of high ovulation rate. In vitro, the most relevant difference is an early acquisition of estrogen production ability of small follicles in Booroola fecundity gene barring ewes. Fluoro-gestone-acetate (FGA) pessaries reduced the number of growing follicles; despite this effect disappearing after the sponge withdrawal, the ovulation rate is significantly reduced. But an equine chorionic gonadotrophin (eCG) treatment restores the ovulation rate (OR) by reducing the atresia rate of pre-ovulatory follicles. In similar conditions, a pretreatment of the ewes with melatonin again reduced the atresia rate of large follicles and resulted in an increased ovulation rate. In vitro, FGA blocked aromatization ability, and melatonin inhibited both androstenedione and estradiol production, but a further treatment with eCG partly restores the steroid secretion. Immunization against androstenedione leads to a higher OR, owning to a reduced atresia of large follicles. Daily growth hormone injections for a hole cycle resulted in an increased follicular population and ovulation rate, while FSH plasma levels decreased and the follicle sensitivity to gonadotrophins was reduced.

Body weight, oestrous and ovarian activity in local Burundian ewes and goats after parturition in the dry season.

To compare body weight losses and post-partum anoestrus, twelve local Burundian ewes and twelve goats which had lambed or kidded at the middle of the dry season were followed from parturition until eight months. Each dam was weighed every month and bled three times a week to assess the ovarian activity resumption by plasma progesterone (P4) profiles. For the two species, the body weight decreased significantly (P < 0.05) compared to the body weight at parturition. The mean time during which the body weight decreased was longer (P < 0.05) for the ewes (3.2 +/- 1.2 months) than for the goats (2.3 +/- 1.4 months), however, the relative body weight losses did not significantly differ. The time to oestrous and ovarian activity resumption was highly correlated to the body weight losses for the ewes (r = 0.81; P < 0.01 and r = 0.58; P < 0.05) not for the goats. The first oestrus preceded the first ovarian activity by 4 days in the goats, but occurred 36 days later in the ewes. Nevertheless, after the first luteal function, the subsequent ovarian activity was regular and normal in the ewes but not in the goats and in some cases a return to anoestrus could be observed. These data indicate that in the ewe, not in the goat, the body weight losses are one of the major limiting factors of the oestrous and ovarian resumption after parturition during the dry season. Moreover, the occurrence of luteal function does not initiate a regular reproductive cyclicity in the goat in contrast to the ewes.