Assessment: Effects of Porcine Zona Pellucida Immunocontraception on Estrous Cyclicity in Feral Horses

Powell, David; Monfort, Steven L.

doi:10.1207/s15327604jaws0404_04

Cited by 23 publications

(18 citation statements)

References 30 publications

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“…Such predictions are not consistent with data from Assateague Island where mares show increased survival, only minimal physiological side effects, and no behavioral or demographic changes [4], [5], [6]. In addition, foal survival does not differ between foals born in or out of the normal foaling season [41].…”

Section: Discussionmentioning

confidence: 68%

Immunocontraception in Wild Horses (Equus caballus) Extends Reproductive Cycling Beyond the Normal Breeding Season

2010

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BackgroundAlthough the physiological effects of immunocontraceptive treatment with porcine zona pellucida (PZP) have been well studied, little is known about PZP's effects on the scheduling of reproductive cycling. Recent behavioral research has suggested that recipients of PZP extend the receptive breeding period into what is normally the non-breeding season.Methodology/Principal FindingsTo determine if this is the case, we compiled foaling data from wild horses (Equus caballus) living on Shackleford Banks, North Carolina for 4 years pre- and 8 years post-contraception management with PZP (pre-contraception, n = 65 births from 45 mares; post-contraception, n = 97 births from 46 mares). Gestation lasts approximately 11–12 months in wild horses, placing conception at approximately 11.5 months prior to birth. Since the contraception program began in January 2000, foaling has occurred over a significantly broader range than it had before the contraception program. Foaling in PZP recipients (n = 45 births from 27 mares) has consistently occurred over a broader range than has foaling in non-recipients (n = 52 births from 19 mares). In addition, current recipients of PZP foaled later in the year than did prior recipient and non-recipient mares. Females receiving more consecutive PZP applications gave birth later in the season than did females receiving fewer applications. Finally, the efficacy of PZP declined with increasing consecutive applications before reaching 100% after five consecutive applications.Conclusions/SignificanceFor a gregarious species such as the horse, the extension of reproductive cycling into the fall months has important social consequences, including decreased group stability and the extension of male reproductive behavior. In addition, reproductive cycling into the fall months could have long-term effects on foal survivorship. Managers should consider these factors before enacting immunocontraceptive programs in new populations. We suggest minor alterations to management strategies to help alleviate such unintended effects in new populations.

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Section: Discussionmentioning

confidence: 68%

Immunocontraception in Wild Horses (Equus caballus) Extends Reproductive Cycling Beyond the Normal Breeding Season

2010

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“…More surprisingly, 4 of 9 females in that study that had only received a single treatment (one primer injection followed by one booster injection) never produced any offspring after 4–8 years of observation. While the mechanism for explaining this protracted infertility in E. ferus przewalskii is unknown, some of the Assateague horses were found to have experienced ovulatory failure [31]. This is not the targeted physiological response of PZP vaccination, and the effect was highly variable between individuals due to the episodic nature of ovulatory failure, as opposed to a chronic condition.…”

Section: Discussionmentioning

confidence: 99%

Contraception can Lead to Trophic Asynchrony between Birth Pulse and Resources

2013

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Abiotic inputs such as photoperiod and temperature can regulate reproductive cyclicity in many species. When humans perturb this process by intervening in reproductive cycles, the ecological consequences may be profound. Trophic mismatches between birth pulse and resources in wildlife species may cascade toward decreased survival and threaten the viability of small populations. We followed feral horses (Equus caballus) in three populations for a longitudinal study of the transient immunocontraceptive porcine zona pellucida (PZP), and found that repeated vaccinations extended the duration of infertility far beyond the targeted period. After the targeted years of infertility, the probability of parturition from post-treated females was 25.6% compared to 64.1% for untreated females, when the data were constrained only to females that had demonstrated fertility prior to the study. Estimated time to parturition increased 411.3 days per year of consecutive historical treatment. Births from untreated females in these temperate latitude populations were observed to peak in the middle of May, indicating peak conception occurred around the previous summer solstice. When the post-treated females did conceive and give birth, parturition was an estimated 31.5 days later than births from untreated females, resulting in asynchrony with peak forage availability. The latest neonate born to a post-treated female arrived 7.5 months after the peak in births from untreated females, indicating conception occurred within 24–31 days of the winter solstice. These results demonstrate surprising physiological plasticity for temperate latitude horses, and indicate that while photoperiod and temperature are powerful inputs driving the biological rhythms of conception and birth in horses, these inputs may not limit their ability to conceive under perturbed conditions. The protracted infertility observed in PZP-treated horses may be of benefit for managing overabundant wildlife, but also suggests caution for use in small refugia or rare species.

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“…In contrast, little evidence for interference with ovarian function has been reported in the mare. A subsequent study in the same population reported no association between the incidence of ovulatory failure in mares and their duration of treatment [12]. A subsequent study in the same population reported no association between the incidence of ovulatory failure in mares and their duration of treatment [12].…”

Section: Introductionmentioning

confidence: 88%

Ovarian function and pregnancy outcome in pony mares following immunocontraception with native and recombinant porcine zona pellucida vaccines

Joone

Bertschinger

Gupta

et al. 2016

Equine Veterinary Journal

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Assessment: Effects of Porcine Zona Pellucida Immunocontraception on Estrous Cyclicity in Feral Horses

Cited by 23 publications

References 30 publications

Immunocontraception in Wild Horses (Equus caballus) Extends Reproductive Cycling Beyond the Normal Breeding Season

Immunocontraception in Wild Horses (Equus caballus) Extends Reproductive Cycling Beyond the Normal Breeding Season

Contraception can Lead to Trophic Asynchrony between Birth Pulse and Resources

Ovarian function and pregnancy outcome in pony mares following immunocontraception with native and recombinant porcine zona pellucida vaccines

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