-The existence of short ovulatory cycles (5-day duration) after the first male-induced ovulations in anovulatory ewes and goats, associated or not with the appearance of oestrous behaviour, is the origin of the two-peak abnormal distribution of parturitions after the "male effect". We propose here a working hypothesis to explain the presence of these short cycles. The male-effect is efficient during anoestrus, when follicles contain granulosa cells of lower quality than during the breeding season. They generate corpora lutea (CL) with a lower proportion of large luteal cells compared to small cells, which secrete less progesterone, compared to what is observed in the breeding season cycle. This is probably not sufficient to block prostaglandin synthesis in the endometrial cells of the uterus at the time when the responsiveness to prostaglandins of the new-formed CL is initiated and, in parallel, to centrally reduce LH pulsatility. This LH pulsatility stimulates a new wave of follicles secreting oestradiol which, in turn, stimulates prostaglandin synthesis and provokes luteolysis and new ovulation(s). The occurrence of a new follicular wave on days 3-4 of the first male-induced cycle and the initiation of the responsiveness to prostaglandins of the CL from day 3 of the oestrous cycle are probably the key elements which ensure such regularity in the duration of the short cycles. Exogenous progesterone injection suppresses short cycles, probably not by delaying ovulation time, but rather by blocking prostaglandin synthesis, thus impairing luteolysis. The existence, or not, of oestrous behaviour associated to these ovulatory events mainly varies with species: ewes, compared to does, require a more intense endogenous progesterone priming; only ovulations preceded by normal cycles are associated with oestrous behaviour. Thus, the precise and delicate mechanism underlying the existence of short ovulatory and oestrous cycles induced by the male effect appears to be dependent on the various levels of the hypothalamo-pituitary-ovario-uterine axis.male-effect / ovulation / corpus luteum / cycle / oestrus / uterus

-The Barbarine sheep is characterised by a fat-tail, whose mass varies between 1 and 4 kg. Its management is traditionally based on spring mating. The ability of this fat-tailed ewe to mobilise its body reserves has been demonstrated in lactation and the dry period by experimentally varying the food supply. The severely underfed ewe (200 g oat hay) can survive 161 days and lose 36% of its body weight (BW), with a change of 8.8 kg of dissected adipose tissue (AT) and 3.4 kg of muscle. It reached this stage with an empty BW of 24 kg containing 12% of AT. The fat tail exerts a role as a body reserve mainly through its mass rather than through its ability to be rapidly mobilised. In such situations, plasma NEFA and 3-hydroxybutyrate concentrations are first almost doubled, then decline in permanently underfed ewes, showing the ability of Barbarine ewes to adjust their lipid metabolite concentration in order to limit the toxic effects of high concentrations and therefore prolong survival. By the end of a re-feeding period, Barbarine ewes returned to their initial BW, lipid and protein mass. This breed has a good fertility, which can, however, be depressed in cases of undernutrition. However, if the mating period is extended, the overall reproductive performance is generally satisfactory. Poor nutrition during pregnancy may reduce lamb birth weight and affect subsequent growth, however, in traditional conditions, ewe and lamb mortality rates are surprisingly low in this breed. In normal birth weighted lambs, the post-weaning growth performances of grazing lambs are moderate but in feedlot conditions the conversion rate is rather low and carcass adiposity is high. This review shows that the Barbarine sheep, and specially the ewe, is well adapted to the local conditions mainly because of its high fertility and its ability to deposit and mobilise body reserves. Elles atteignent cet état avec un PV vide de 24 kg contenant 12 % de TA. Le gras caudal agit comme réserve corporelle plutôt par sa masse que par son aptitude à être mobilisé rapidement. Dans de telles conditions, les concentrations plasmatiques en AGNE et 3-hydroxybutyrate sont transitoirement doublées puis elles déclinent, chez les brebis toujours sous-alimentées, montrant la capacité de la Barbarine à ajuster la concentration des métabolites lipidiques pour limiter les effets toxiques des fortes concentrations et prolonger la survie. En fin de période de réalimentation, les brebis Barbarine retournent à leur PV et masses lipidique et protéique initiales. Cette race a une fertilité satisfaisante, qui peut diminuer en cas de sous-nutrition. Cependant, si la période de lutte est suffisamment longue, la fertilité s'améliore. La sous-nutrition durant la gestation peut entraîner une réduction du poids des agneaux à la naissance. Cependant et dans de telles conditions, le taux de mortalité des agneaux est étonnamment faible. Chez des agneaux à poids de naissance normal, la croissance post-sevrage est modérée au pâturage mais, en bergerie, elle reste faible av...

L’introduction des béliers dans un groupe de brebis en anoestrus anovulatoire induit dans les 2 à 4 jours une ovulation silencieuse, c’est-à-dire non associée à un comportement de chaleur, suivie soit par un cycle ovulatoire de durée ’normale’ (voisine de 17 jours) puis d’une nouvelle ovulation associée à un comportement de chaleur, soit par un cycle ovulatoire de durée courte mais constante (6 jours) suivi d’une nouvelle ovulation silencieuse puis, après un cycle ovulatoire de durée normale, par une nouvelle ovulation associée à un comportement d’oestrus. Il en résulte que les premières chaleurs apparaissent très tardivement chez les femelles dont l’activité sexuelle est induite par l’introduction des béliers, ce qui se traduit par deux pics d’activité sexuelle situés environ 18 à 20 jours et 24 à 26 jours après l’introduction des béliers. Les brebis non gravides reviennent normalement en oestrus sauf si l’anoestrus est intense au moment attendu de ces retours (plus de un mois après induction de la première ovulation). L’article présente les connaissances acquises ces dernières années sur les mécanismes physiologiques impliqués dans l’induction de l’ovulation par l’effet bélier et donne quelques règles d’utilisation de cette méthode dans les élevages, tout en précisant ses limites. Les deux points essentiels pour utiliser efficacement cette technique sont d’une part, la connaissance des aptitudes de reproduction (saisonnement) de la race dans son milieu et, d’autre part, la possibilité de séparer les mâles des femelles pendant une durée minimale de un mois préalablement à leur mise en contact physique.

Summary -The involvement of the uterus in early regression of corpora lutea induced by the ram effect was studied in seasonally anoestrous Barbarine ewes. In experiment 1, group I was only submitted to the male effect (control, n = 15) while group II (n = 14) was injected every 12 h with flunixin meglumine, a PGF2a synthetase inhibitor (finadyne), from day 3 to day 6 (day 0: day of ram introduction). The preovulatory LH surge appeared at the same time (around 21 h after ram introduction) in both groups. Finadyne treatment significantly decreased 13-14-dihydro-15-keto-PGF2a (PGFM) pulses ( 1.3 ± 0.3 versus 0.4 ± 0.2; P < 0.05), the number of short cycles (50 versus 14%, P < 0.05), and provided a single peak of oestrus, 15-16 days after the introduction of the rams, instead of between day 14 and day 23 (P < 0.01 In experiment 2, 17 hysterectomized ewes were allocated into two groups: group III (n = 8) was injected with oil and group IV (n = 9) received an intramuscular injection of 20 mg of progesterone immediately before introduction of rams. An additional group of intact ewes was used as control (group V, n = 9). Hysterectomy did not affect the ovulation response to the ram effect, but completely suppressed short cycles (0 versus 78% , P < 0.001). The preovulatory LH surge was delayed in hysterectomized females (36.0 ± 14.1 versus 16.6 ± 11.4 h; P < 0.004). Treatment with progesterone significantly (P < 0.01) increased the interval between introduction of rams and the preovulatory LH surge. In conclusion, suppression of short cycles by hysterectomy and an inhibitor of PGF2a synthetase suggest that the uterus is essential for determining the lifespan of ram-induced corpora lutea and that premature release of PGF2a is the cause of early luteal regression. The hypothesis that lower secretion of progesterone before D5 could be the initial cause of the premature induction of the luteolytic signal is discussed.

(May). In both experiments, half of the females received 20 mg of progesterone intramuscularly just before male introduction (day 0). Blood samples were taken at 4 h intervals from the time of introduction of the ram, for the determination of the time of the preovulatory LH surge in response to the 'ram effect' (Exp 1) and once a day from days 1 to 8 to determine plasmatic progesterone concentrations (Exp 1, Exp 2). The ovulation rate was determined by coelioscopy at days 4 and 9, and c!strus behaviour was monitored twice daily in each experiment. In the ewe, progesterone delayed the time of the preovulatory LH surge (58.8± 10.1 vs 20.5 10.7 h, P < 0.001), and suppressed hypofunctional corpora lutea (0/15 vs 7114, P < 0.001). The induced ovulation rate was not significantly different between control and treated females (1.50± 0.52 vs 1.26± 0.46 respectively). Only 1 female in the control group and 2 in the treated group showed cestrus behaviour at the induced ovulation. Suppression of short cycles by progesterone treatment allowed synchronization of oestrus between days 17 and 20 compared to days 14 and 23 in the control group (P < 0.001). In the goat, all induced ovulations in the control group were followed by a short cycle. in the progesterone-treated group, 3 out of 20 goats developed abnormal induced corpora lutea (P < 0.001). First oestrus occurred between days 1 and 8 in control group and between days 2 and 3 in treated goats. Treatment with progesterone increased the percentage of females showing oestrus at induced ovulation (100 vs 35%, P < 0.001). The ovulation rate at first oestrus was increased in treated goats (1.85 vs 1.35, P < 0.001). In conclusion, 20 mg progesterone administered at day 0 is efficient at preventing the occurrence of short ovarian cycles. After ovulation induced by the male effect, the percentage of females in oestrus, and the induced ovulation rate are increased by progesterone treatment.