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PloS one2010; 5(10); e13635; doi: 10.1371/journal.pone.0013635

Immunocontraception in wild horses (Equus caballus) extends reproductive cycling beyond the normal breeding season.

Abstract: Although 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. Results: To 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: For 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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Publication Date: 2010-10-26 PubMed ID: 21049017PubMed Central: PMC2964306DOI: 10.1371/journal.pone.0013635Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research article explores the impact of immunocontraception treatment using porcine zona pellucida (PZP) on the reproductive cycle of wild horses. The study found that PZP treatment extended the breeding season beyond its normal schedule, which could potentially disrupt social structures among horse populations and affect foal survival rates.

Study Purpose and Methodology

The study focused on understanding the effects of the immunocontraceptive treatment PZP on the reproductive cycle of wild horses (Equus caballus). Previous physiological studies on PZP’s effects were extensively referenced, but its impact on reproductive scheduling had not been studied in depth. The behavior of horses receiving PZP suggested an extension beyond the usual breeding period into the non-breeding season.

The scientists used foaling data from wild horses on Shackleford Banks, North Carolina, collected over four years before and eight years after contraceptive management with PZP commenced. The gestation period for horses lasts approximately 11-12 months, allowing them to estimate the time of conception as 11.5 months prior to birth. By comparing birth records pre and post contraception, they were able to assess the impact of PZP administration on the breeding cycle.

Findings and Implications

  • Since the commencement of the contraceptive program in 2000, the range of foaling had significantly widened. Mares receiving PZP had their foaling spread across a broader range as compared to those who were not on the program.
  • PZP recipients also gave birth later in the year as compared to non-recipients. Furthermore, mares receiving more consecutive applications of PZP gave birth even later in the season.
  • The study noted a decline in the efficacy of PZP with each consecutive administration until it reached 100% after five consecutive applications.

These findings point to significant modifications to wild horse behavior due to PZP influenced protraction of the breeding season. Such changes have socio-behavioral implications as the horse is a highly social species.

Extended breeding season results in decreased group stability and prolongs male reproductive behavior. This, in turn, could lead to potential long-term impacts on foal survivorship.

Recommendations and Conclusions

Given these findings, the researchers recommend that wildlife managers should account for these potential social and population-level impacts when implanting immunocontraceptive programs. They suggest slight alterations in management strategies to mitigate any unintended consequences in fresh populations. Through a better understanding of the broad effects of immunocontraception with PZP, future management of wild horse populations can be more comprehensive and aware of potential side effects.

Cite This Article

APA
Nuñez CM, Adelman JS, Rubenstein DI. (2010). Immunocontraception in wild horses (Equus caballus) extends reproductive cycling beyond the normal breeding season. PLoS One, 5(10), e13635. https://doi.org/10.1371/journal.pone.0013635

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 5
Issue: 10
Pages: e13635

Researcher Affiliations

Nuñez, Cassandra M V
  • Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America. cmvnunez@princeton.edu
Adelman, James S
    Rubenstein, Daniel I

      MeSH Terms

      • Animals
      • Animals, Wild / physiology
      • Contraception, Immunologic / veterinary
      • Female
      • Horses / physiology
      • Reproduction

      Conflict of Interest Statement

      Competing Interests: The authors have declared that no competing interests exist.

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      This article has been cited 14 times.
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