Effect of the rate of progesterone decline at luteolysis on the ovulatory follicles and subsequent estrous cycle length in ewes

Time of ovulation and pregnancy outcomes obtained with the prostaglandin-based protocol Synchrovine for FTAI in sheep

The objective of the present study was to determine the ovarian response induced with the prostaglandin-based protocol Synchrovine (two doses of PGF_2α given 7 d apart), as well as the fertility after FTAI. In Experiment 1, 15 females received the Synchrovine protocol using two different PGF_2α analogues (Delprostenate vs. D-Cloprostenol). No differences in estrus response, time of ovulation and follicular dynamics were found between both groups (P < 0.05). The ovulation after Synchrovine was synchronized in a similar mean interval (68.8 ± 7.1 h) than when the females received a single dose of PGF_2α (70.2 ± 20.7 h; P=NS), but the dispersion between the first and the last ovulation was reduced with this protocol (range 60-84 h vs. 24-96 h, respectively; P < 0.05). In experiment 2, 318 ewes were treated with the Synchrovine protocol and cervical FTAI was performed using different sperm cell concentrations. Pregnancy rate was higher using 200 × 10⁶ and 100 × 10⁶ sperm cells (38.2%, 39/102; and 34.9%, 38/109, respectively) than using 50 × 10⁶ (23.4%, 25/107, P < 0.05). In Experiment 3, 444 ewes received the Synchrovine protocol and were assigned to receive 300 IU of eCG or not at the moment of the second dose of PGF_2α, and cervical FTAI was performed 42 h or 48 h after the second dose of PGF_2α. No effect was found related to the eCG administration nor the time of insemination. In Experiment 4, 342 received cervical or intrauterine insemination after treatment with the Synchrovine protocol, resulting in greater pregnancy rate for intrauterine insemination than cervical insemination (52.5%, 90/171 vs. 31%, 53/171, P < 0.05). These experiments demonstrate that the Synchrovine protocol effectively induces luteolysis, estrus and ovulation in most of the treated females, and ovulation is synchronized into a narrow window of 24 h. Pregnancy rate obtained with cervical FTAI is around 30-45%, with similar results using 100 × 10⁶ or 200 × 10⁶ sperm cells, the eCG administration seems not to be necessary, the type of PGF2α analogue does not appear relevant, and fertility is improved with intrauterine semen deposition.

Effect of the combination of male effect with PGF2α on estrus synchronization of hair sheep in Mexican tropic

The aim of this study was to evaluate the "male effect" at the end of protocol with prostaglandins (PG) on estrus synchronization of hair sheep during breeding season (November-December) in Yucatan, Mexico. Twenty female Pelibuey sheep (weighting 38.2 ± 1.6 kg and body condition score of 2.5 ± 0.5) were randomly distributed in two groups (n = 10). Group T1 (control, PG), two doses of 50 μg of cloprostenol with 12 days between applications were applied; in the second group T2 (PG-ME), ewes received the same PG protocol plus the introduction of a male at the end of treatment. The interval of end treatment-onset of estrus was analyzed using survival test; the number of sheep with presence/absence of estrus was analyzed using Fisher's exact test. Ewes in estrus for groups T1 and T2 were 5 vs. 8, respectively. No significant differences were found as regards the interval end of treatment-onset of estrus (P > 0.05), as well as in total proportion of ewes with estrus and likewise in the duration of it (P > 0.05). We conclude that the protocol based on double dose of PGF2α with interval of 12 days combined with the male effect is efficient to induce luteolysis and estrus synchronization in hair sheep.

The use of prostaglandins in controlling estrous cycle of the ewe: a review

This review considers the use of prostaglandin F(2α) and its synthetic analogues (PG) for controlling the estrous cycle of the ewe. Aspects such as phase of the estrus cycle, PG analogues, PG doses, ovarian follicle development pattern, CL formation, progesterone synthesis, ovulation rate, sperm transport, embryo quality, and fertility rates after PG administration are reviewed. Furthermore, protocols for estrus synchronization and their success in timed AI programs are discussed. Based on available information, the ovine CL is refractory to PG treatment for up to 2 days after ovulation. All PG analogues are effective when an appropriate dose is given; in that regard, there is a positive association between the dose administered and the proportion of ewes detected in estrus. Follicular response after PG is dependent on the phase of the estrous cycle at treatment. Altered sperm transport and low pregnancy rates are generally reported. However, reports on alteration of the steroidogenic capacity of preovulatory follicles, ovulation rate, embryo quality, recovery rates, and prolificacy, are controversial. Although various PG-based protocols can be used for estrus synchronization, a second PG injection improves estrus response when the stage of the estrous cycle at the first injection is unknown. The estrus cycle after PG administration has a normal length. Prostaglandin-based protocols for timed AI achieved poor reproductive outcomes, but increasing the interval between PG injections might increase pregnancy rates. Attempts to improve reproductive outcomes have been directed to provide a synchronized LH surge: use of different routes of AI (cervical or intrauterine), different PG doses, and increased intervals between PG injections. Finally we present our point of view regarding future perspectives on the use of PG in programs of controlled sheep reproduction.

Progesterona plasmática e fertilidade de fêmeas caprinas submetidas à sincronização do estro com prostaglandina F2α

Avaliou-se a resposta ao protocolo de sincronização do estro com duas doses de prostaglandina F2a (22,5µg) intervaladas de 10 dias, por meio da mensuração da concentração de progesterona plasmática, bem como a taxa de concepção das cabras após a inseminação artificial, de acordo com as diferentes respostas obtidas. Utilizaram-se 23 fêmeas e dois reprodutores da raça Toggenburg. A mensuração da progesterona plasmática foi realizada no dia da primeira aplicação de PGF2a (D0), no D5, no dia da segunda aplicação de PGF2a (D10), no D15, no D20 e no D33. A resposta positiva à PGF2α foi determinada pela queda da concentração de progesterona a valores abaixo de 1,5ng/mL, mensurada nos dias cinco e 15. As fêmeas foram distribuídas em três grupos. O grupo I foi composto por fêmeas que responderam às duas aplicações; o grupo II por fêmeas que não responderam à primeira aplicação e responderam à segunda aplicação; e o grupo III por fêmeas que responderam à primeira aplicação e não responderam à segunda aplicação, foram inseminadas e não conceberam. A presença de um corpo lúteo funcional, no momento das aplicações, determinou a resposta ao protocolo. As diferentes respostas das fêmeas ao protocolo, grupo I e II, não influenciaram as taxas de concepção.

Amounts of an estrogen receptor β isoform increased in the theca of preovulatory follicles of sheep

Determination of the specific roles of the estrogen receptor (ER) forms in reproductive processes of different species remains incomplete. In the present experiment, cellular localization and changes in relative amounts of the ERα and ERβ in late developing ovarian follicles, oviduct, and uterus were determined during the follicular phase of the estrous cycle in sheep. Ewes in mid-luteal phase were treated with prostaglandin F(2α) (PG) to induce luteolysis and control the onset of the follicular phase. The oviducts, uterus, and the ovaries were collected at 0 (ewes not treated with PG), 4, 18, and 36 h after PG treatment (early, mid, and late follicular phase, respectively) and processed to evaluate the ERs using immunohistochemical (IHC) procedures. The ERα was localized to nuclei of granulosa cells of late developing follicles and most cells of the oviduct and uterus. The ERβ was detected only in ovarian follicles using two antibodies directed to different regions of the ERβ. Western immunoblotting demonstrated that the antibody directed against the N-terminal region of the ERβ detected one isoform (approximately 53 kDa) whereas the antibody directed against the C-terminus detected two ERβ isoforms (approximately 53 kDa and 59 kDa). Western and IHC results combined indicated presence of the 59 kDa ERβ in granulosa cells and the 53 kDa ERβ in both granulosa and theca cells. Relative amounts (immunostaining intensity) of the ERα increased (P<.05) in granulosa cells of preovulatory follicles and in the isthmian muscularis of the oviduct at the late follicular phase. Amounts of the ERα in the mucosal epithelium of the oviductal regions (isthmus, ampulla, and infundibulum), and in various uterine cell types (glandular and luminal epithelia, endometrial stromal cells, and myometrium) did not change (P>.05) throughout the follicular phase. A major increase (four-fold) in expression of the 53 kDa ERβ in the theca and a less pronounced increase in the granulosa occurred at the late follicular phase. The ERα is broadly expressed in reproductive organs of sheep and is upregulated only in few cell types during the late follicular phase. Immunoreactive ERβ was detected only in the ovary. Important estrogen actions in theca cells during preovulatory follicular development likely occur in association with a major increase in expression of an ERβ isoform.

Prostaglandin F2α-induced estrus in ewes exhibiting estrous cycles of different duration

Effects of prostaglandin F(2alpha) (PGF(2alpha)), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (< or =16.5 days, short-cycle ewes, n = 10) or long (> or =18 days, long-cycle ewes, n = 9) based on the durations of two estrous cycles (cycles -2 and -1) before treatment. The ewes received (i.m.) 20mg of PGF(2alpha) on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 microg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF(2alpha) and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF(2alpha) and GnRH treatment on cycle 0 was not different (P > 0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner (P < 0.05) after PGF(2alpha) injection in short-cycle ewes than in long-cycle ewes (1.9 +/- 0.1 days and 2.3 +/- 0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer (P < 0.01) than cycle -1 in short-cycle ewes. However, duration of estrous cycle +1 did not change (P > 0.05) after PGF(2alpha) and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ (P > 0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17beta in follicular fluid between short- and long-cycle ewes after PGF(2alpha) and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF(2alpha) and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.

New treatments associated with timed artificial insemination in small ruminants

Timed artificial insemination (TAI) is a very important tool in production systems, as it has a direct impact on cost-efficiency by reducing labour resulting from oestrus detection. However, to make TAI commercially feasible, hormonal treatments need to assure acceptable pregnancy rates and be economically viable. Recent advances in the knowledge of ovarian physiology (e.g. determination of follicular waves, sensitivity of the early corpus luteum) in small ruminants allowed the development of new treatments focused on an efficient estimation and synchronisation of the time of ovulation of the females of a treated flock/herd. In this review we summarise new information and concepts in the hormonal control of the life span of the corpus luteum, as well as methods to manipulate follicular growth in small ruminants. Additionally, we elaborate on recent studies concerning the use of TAI associated with short progestogen treatment in goats and the newly developed Synchrovine™ protocol (two doses of prostaglandin F2α given seven days apart) in sheep.

Response of the 1-5 day-aged ovine corpus luteum to prostaglandin F2alpha

The hypothesis that, in the ewe, prostaglandin (PG) F2alpha administration on day 3 after ovulation is followed by luteolysis and ovulation was tested using 24 animals. The ewes were treated with a dose of a PGF2alpha analogue (delprostenate, 160 microg) on days 1 (n=8), 3 (n=8) or 5 (n=8) after ovulation, was established by transrectal ultrasonography. Daily scanning and blood sampling were performed to determine ovarian changes and progesterone serum concentrations by radioinmunoassay. The treatment induced a sharp decrease of progesterone concentrations followed by oestrus and ovulation in all ewes treated on days 3 and 5 and in one ewe treated on day 1 (8/8, 8/8, 1/8; P<0.05). Seven ewes treated on day 1 did not respond to PGF2alpha treatment and had an inter-ovulatory cycle of normal length (17.4 +/- 0.5 days). However, the profile of progesterone concentrations during the cycle of these ewes was delayed 1 day (P<0.05) compared with a control cycle. The overall interval between PGF2alpha and oestrus for the 17 responding ewes was 42.4 +/- 2.3 h. In 15 of these ewes the ovulatory follicle was originated from the first follicular wave and the ovulation occurred at 60.8 +/- 1.8 h after PGF2alpha treatment. The other two responding ewes ovulated an ovulatory follicle originated from the second follicular wave between 72 and 96 h after treatment. These results support the hypothesis and suggest that refractoriness to PGF2alpha of the recently formed corpus luteum (CL) may be restricted to the first 1-2 days post-ovulation.

Luteolysis: a neuroendocrine-mediated event

In many nonprimate mammalian species, cyclical regression of the corpus luteum (luteolysis) is caused by the episodic pulsatile secretion of uterine PGF2alpha, which acts either locally on the corpus luteum by a countercurrent mechanism or, in some species, via the systemic circulation. Hysterectomy in these nonprimate species causes maintenance of the corpora lutea, whereas in primates, removal of the uterus does not influence the cyclical regression of the corpus luteum. In several nonprimate species, the episodic pattern of uterine PGF2alpha secretion appears to be controlled indirectly by the ovarian steroid hormones estradiol-17beta and progesterone. It is proposed that, toward the end of the luteal phase, loss of progesterone action occurs both centrally in the hypothalamus and in the uterus due to the catalytic reduction (downregulation) of progesterone receptors by progesterone. Loss of progesterone action may permit the return of estrogen action, both centrally in the hypothalamus and peripherally in the uterus. Return of central estrogen action appears to cause the hypothalamic oxytocin pulse generator to alter its frequency and produce a series of intermittent episodes of oxytocin secretion. In the uterus, returning estrogen action concomitantly upregulates endometrial oxytocin receptors. The interaction of neurohypophysial oxytocin with oxytocin receptors in the endometrium evokes the secretion of luteolytic pulses of uterine PGF2alpha. Thus the uterus can be regarded as a transducer that converts intermittent neural signals from the hypothalamus, in the form of episodic oxytocin secretion, into luteolytic pulses of uterine PGF2alpha. In ruminants, portions of a finite store of luteal oxytocin are released synchronously by uterine PGF2alpha pulses. Luteal oxytocin in ruminants may thus serve to amplify neural oxytocin signals that are transduced by the uterus into pulses of PGF2alpha. Whether such amplification of episodic PGF2alpha pulses by luteal oxytocin is a necessary requirement for luteolysis in ruminants remains to be determined. Recently, oxytocin has been reported to be produced by the endometrium and myometrium of the sow, mare, and rat. It is possible that uterine production of oxytocin may act as a supplemental source of oxytocin during luteolysis in these species. In primates, oxytocin and its receptor and PGF2alpha and its receptor have been identified in the corpus luteum and/or ovary. Therefore, it is possible that oxytocin signals of ovarian and/or neural origin may be transduced locally at the ovarian level, thus explaining why luteolysis and ovarian cyclicity can proceed in the absence of the uterus in primates. However, it remains to be established whether the intraovarian process of luteolysis is mediated by arachidonic acid and/or its metabolite PGF2alpha and whether the central oxytocin pulse generator identified in nonprimate species plays a mediatory role during luteolysis in primates. Regardless of the mechanism, intraovarian luteolysis in primates (progesterone withdrawal) appears to be the primary stimulus for the subsequent production of endometrial prostaglandins associated with menstruation. In contrast, luteolysis in nonprimate species appears to depend on the prior production of endometrial prostaglandins. In primates, uterine prostaglandin production may reflect a vestigial mechanism that has been retained during evolution from an earlier dependence on uterine prostaglandin production for luteolysis.