Melengestrol Acetate at Greater Doses than Typically Used for Estrous Synchrony in Bovine Females Does not Mimic Endogenous Progesterone in Regulation of Secretion Of Luteinizing Hormone and 17β-Estradiol1

Kojima, F. N.; Chenault, J.R.; Wehrman, M. E.; Bergfeld, E. G. M.; Cupp, Andrea S.; Werth, L. A.; Mariscal, V.; Sánchez, Tania; Kittok, R. J.; Kinder, J. E.

doi:10.1095/biolreprod52.2.455

Cited by 54 publications

(37 citation statements)

References 38 publications

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“…In a recent study (Custer et al 1994), the dominant follicle persisted in 10 of 23 cattle treated with MGA for 7 d, starting on day 17 of the cycle; the low plasma progestagen concentrations in MGA-treated cattle without a functional corpus luteum resulted in increased LH pulse frequencies but insufficient LH release to cause ovulation (Kojima et al 1995). Following cessation of MGA treatment, ovulation occurred with an aged oocyte from the persistent follicle (Custer et al 1994).…”

Section: Discussionmentioning

confidence: 97%

“…However, this hypothesis was not supported. In a recent study (Kojima et al 1995) reported after completion of exp. 1, it was shown that 1 mg d -1 MGA was unable to suppress LH pulse frequency, and as a result follicular size and plasma estrogen concentrations increased.…”

Section: Discussionmentioning

confidence: 99%

“…This regimen effectively synchronized estrus but pregnancy rates were lower in cattle that were late in the estrous cycle at the start of MGA treatment compared with those that were early. When this regimen is started late in the estrous cycle, the corpus luteum regresses, ovarian follicles become very large and plasma estrogen concentrations increase (Zimbelman and Smith 1966;Custer et al 1994;Kojima et al 1995). This regimen has been recently modified to include treatment with 5 mg E-17β on the first day that MGA is fed (Kastelic et al 1996).…”

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confidence: 99%

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Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle

Kastelic¹,

McCartney²,

Olson³

et al. 1997

Can. J. Anim. Sci.

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Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle. Can. J. Anim. Sci. 77: 683-688. Four experiments were conducted to investigate the use of melengesterol acetate (MGA) and estradiol-17β (E-17β) for synchronizing estrus and improving reproductive performance in beef cattle. Synchronized pregnancy rates were higher (P < 0.05) in heifers fed MGA after AI than controls (4 of 9 versus 0 of 7, respectively), but were not different for cows (20 of 37, 54% versus 23 of 40, 58%). Estrus rate (percentage of cows detected in estrus) was higher (P < 0.05) for cows treated with E-17β + MGA compared with those treated with cloprostenol alone (85.0 versus 65.9%). Synchronized pregnancy rates were not significantly affected by feeding MGA or grain only after detected estrus and AI (20 of 31, 64% versus 17 of 30, 57%). For 20 cows not detected in estrus and bred 100 h after cloprostenol treatment, pregnancy rate was higher (P < 0.05) for those fed MGA after AI than controls (6 of 11, 54% versus 1 of 9, 11%). Feeding MGA after breeding may help to improve pregnancy rates.. Utilisation de l'acétate de melengestrol (MGA) et de l'estradiol-17β pour la synchronisation de l'oestrus et pour l'amélioration des performances de reproduction chez les bovins à viande. Can. J. Anim. Sci. 77: 683-688. Quatre expériences ont été réalisées pour examiner la valeur de l'acé-tate de melengestrol (MGA) et de l'estradiol-17β (E-17β) pour la synchronisation des chaleurs et pour l'amélioration des performances de reproduction chez les bovins à viande. Les taux de synchronisation des gestations étaient plus élevés (P < 0,05) chez les génisses recevant MGA après IA que chez les génisses témoins (4 sur 9 contre 0 sur 7). Ces différences ne se retrouvaient pas chez les vaches adultes (20 sur 37, 54 % contre 23 sur 40, 58 %). Le taux de déclenchement des chaleurs, c.-à-d. le pourcentage de vaches en chaleurs détectées était plus élevé (P < 0,05) chez les vaches traitées à la fois à E-17β et à MGA que chez celles ne recevant que le cloprosténol (85 contre 65,9 %). Le taux de synchronisation de la gestion ne variait pas significativement selon que les bêtes recevaient du MGA ou seulement du grain après la détection des chaleurs et l'insémination, soit 20 sur 31, 64 % con-tre 17 sur 30, 57 %. Pour les 20 vaches dont on n'avait pas détecté les chaleurs et qui étaient mises à la reproduction 100 h après le traitement au cloprosténol, le taux de gravidité était plus important (P < 0,05) chez les bêtes recevant MGA après insémination que chez les témoins, soit 6 sur 11, 54 % contre 1 sur 9, 11 %. Il semble que l'administration de MGA après la mise à la reproduction puisse améliorer le taux de gestation. Mots clés: Acétate de melengestrol, estradiol-17β, oestrus, performance de reproduction, bovin à viande Melengestrol acetate, a synthetic progestin, has been used in various regimens for estrus synchronization (Patterson et al. 1989; Odde 1990). Advantages of MGA include low cost (e.g. $0.04 hd-1...

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle

Kastelic¹,

McCartney²,

Olson³

et al. 1997

Can. J. Anim. Sci.

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“…In other studies (Macmillan et al 1991;Van Cleef et al 1991), progesterone treatment after breeding improved pregnancy rates, although the increase was significant only when pregnancy rates in untreated cattle were relatively low. Perhaps progesterone would be more efficacious, as it causes more profound suppression of the hypothalamicpituitary axis than MGA (Kojima et al 1995) and therefore may be more effective for sustaining pregnancy. Another alternative is hCG, which has improved pregnancy rates when injected a few days after breeding (Walton et al 1990;Sianangama and Rajamahendran 1992).…”

Section: Discussionmentioning

confidence: 99%

“…This regimen effectively synchronizes estrus, but pregnancy rates are lower in cattle that are late in the estrous cycle at the start of MGA treatment compared with those that are early. When this regimen is started late in the estrous cycle, the corpus luteum regresses, a dominant ovarian follicle becomes large and persists, and plasma estrogen concentrations increase (Custer et al 1994;Kojima et al 1995). This regimen has been recently modified to include treatment with 5 mg E17β (and 100 mg progesterone) on day 1 (Kastelic et al 1996).…”

Section: Mots Clésmentioning

confidence: 99%

Melengestrol acetate, estradiol-17β and GnRH for synchronization of estrus and ovulation in beef cows

Thundathil¹,

Kastelic²,

Olson³

et al. 1999

Can. J. Anim. Sci.

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β and GnRH for synchronization of estrus and ovulation in beef cows. Can. J. Anim. Sci. 79: [39][40][41][42][43]. Three experiments were conducted with suckled crossbred beef cows to determine the efficacy of various short-term regimens for synchronizing estrus or ovulation and to determine whether feeding melengestrol acetate (MGA) after timed AI will increase pregnancy rate. In exp. 1, all cows (n = 141) were given 0.5 mg MGA head -1 d -1 for 7 d (days 1 to 7), 1 or 5 mg E17β (and 100 mg progesterone) or 100 µg GnRH on day 1, and 500 µg cloprostenol on day 7. There were no significant differences among groups for estrous or synchronized conception rates (average, 84.4 and 52.1%, respectively). With an identical protocol in exp. 2 (78 cows), by day 11, cows given 5 mg E17β had the highest estrous and synchronized pregnancy rates (65.4 and 42.3%), compared to 1 mg E17β (46.2 and 15.4%) and GnRH (34.6 and 11.5%). Cows not detected in estrus were timed-inseminated and given 100 µg GnRH, 100 h after cloprostenol. There were no significant differences among groups for synchronized conception rate to timed AI (65.0%) or synchronized pregnancy rate to all inseminations (56.4%). Overall, 5 mg E17β gave the most consistent results. In exp. 3, 84 cows were given 100 µg GnRH on days 1 and 9, 500 µg cloprostenol on day 7, and were timed-inseminated on day 10. Half were fed MGA (0.5 mg head -1 d -1 ) on days 16 to 22, but the pregnancy rate was not different from that in the remaining cows (55.0 versus 47.8%, P > 0.5).

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Melengestrol acetate implant contraception in addax (Addax Nasomaculatus) and Arabian oryx (Oryx Leucoryx)

Hall-Woods

Bauman

et al. 2007

Zoo Biology

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Melengestrol acetate (MGA) implants were used for contraception in three addax and three Arabian oryx females housed at the Saint Louis Zoo. Serum estradiol and progesterone or fecal estrogen and progestin analysis and ultrasonography of reproductive tracts were used for monitoring changes before, during, and after MGA treatment. Follicular development and irregular uterine fluid accumulation were detected in all females during MGA treatment. Although housed with an intact male for all or most of the contraceptive period, no pregnancies occurred.One female addax may have ovulated, based on sustained elevated progesterone levels, and another showed continued follicle development, as seen by fluctuating estradiol concentrations. Reversibility was documented in two of the three addax that resumed reproductive cycles post-MGA-implant removal, whereas the third, a peripubertal female, did not cycle before, during, or after treatment. Addax females were lost to further follow-up after transfer to another institution, so the possibility of subsequent pregnancies is not known.All three Arabian oryx ovulated during the initial MGA treatment, but two of the three females had implants past the typical 2-year efficacy period. They had regular ovulatory cycles after implant removal, with mean cycle length of 27.5+/-1.5 days and mean luteal phase duration of 15.2+/-0.7 days. Reversibility was further shown in all three oryx by pregnancies after placement with a male approximately 2 years after MGA implant removal. Two produced healthy calves, but the third died owing to an unrelated terminal illness in the mother. Zoo Biol 26:299-310, 2007. (c) 2007 Wiley-Liss, Inc.

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Melengestrol Acetate at Greater Doses than Typically Used for Estrous Synchrony in Bovine Females Does not Mimic Endogenous Progesterone in Regulation of Secretion Of Luteinizing Hormone and 17β-Estradiol1

Cited by 54 publications

References 38 publications

Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle

Melengestrol acetate and estradiol-17β for synchronizing estrus and improving reproductive performance in beef cattle

Melengestrol acetate, estradiol-17β and GnRH for synchronization of estrus and ovulation in beef cows

Melengestrol acetate implant contraception in addax (Addax Nasomaculatus) and Arabian oryx (Oryx Leucoryx)

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