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

Nuñez CM, Adelman JS, Rubenstein DI - PLoS ONE (2010)

Bottom Line: Since the contraception program began in January 2000, foaling has occurred over a significantly broader range than it had before the contraception program.In addition, reproductive cycling into the fall months could have long-term effects on foal survivorship.We suggest minor alterations to management strategies to help alleviate such unintended effects in new populations.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America. cmvnunez@princeton.edu

ABSTRACT

Background: 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.

Methodology/principal findings: 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/significance: 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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PZP efficacy and number of consecutive PZP applications.PZP efficacy was defined as the number of recipient mares that did not become pregnant divided by the total number of mares receiving the vaccine. Across the first four consecutive applications, PZP efficacy declined, returning to 100% after five or more consecutive applications (5–7 applications have been shown to result in ovulation failure and decreased oestrogen levels [5], [40]).
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pone-0013635-g004: PZP efficacy and number of consecutive PZP applications.PZP efficacy was defined as the number of recipient mares that did not become pregnant divided by the total number of mares receiving the vaccine. Across the first four consecutive applications, PZP efficacy declined, returning to 100% after five or more consecutive applications (5–7 applications have been shown to result in ovulation failure and decreased oestrogen levels [5], [40]).

Mentions: We defined PZP efficacy during the year of administration as the number of vaccinated mares that did not became pregnant divided by the total number receiving the vaccine. Across the first four consecutive PZP applications, this efficacy declined from 97% to 87%, returning to 100% after five or more consecutive applications (see Fig. 4). A generalized mixed effects model shows that this pattern is significant, even when controlling for mare age (overall model with binomial error distribution: Log Likelihood = −61.79, P = 0.01, generalized r2 = 0.17; consecutive PZP applications: estimate = 2.98, SE = 1.20, z = 2.49, P = 0.01; (consecutive PZP applications)2: estimate = −0.51, SE = 0.22, z = −2.33, P = 0.02; age at first PZP application: estimate = 0.10, SE = 0.05, z = 1.84, P = 0.07). Prior research has shown that five to seven years of consecutive PZP treatment can be associated with ovulation failure [4]. The present dataset is consistent with this result, as no mare receiving the vaccine for five or more consecutive years became pregnant.


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

Nuñez CM, Adelman JS, Rubenstein DI - PLoS ONE (2010)

PZP efficacy and number of consecutive PZP applications.PZP efficacy was defined as the number of recipient mares that did not become pregnant divided by the total number of mares receiving the vaccine. Across the first four consecutive applications, PZP efficacy declined, returning to 100% after five or more consecutive applications (5–7 applications have been shown to result in ovulation failure and decreased oestrogen levels [5], [40]).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2964306&req=5

pone-0013635-g004: PZP efficacy and number of consecutive PZP applications.PZP efficacy was defined as the number of recipient mares that did not become pregnant divided by the total number of mares receiving the vaccine. Across the first four consecutive applications, PZP efficacy declined, returning to 100% after five or more consecutive applications (5–7 applications have been shown to result in ovulation failure and decreased oestrogen levels [5], [40]).
Mentions: We defined PZP efficacy during the year of administration as the number of vaccinated mares that did not became pregnant divided by the total number receiving the vaccine. Across the first four consecutive PZP applications, this efficacy declined from 97% to 87%, returning to 100% after five or more consecutive applications (see Fig. 4). A generalized mixed effects model shows that this pattern is significant, even when controlling for mare age (overall model with binomial error distribution: Log Likelihood = −61.79, P = 0.01, generalized r2 = 0.17; consecutive PZP applications: estimate = 2.98, SE = 1.20, z = 2.49, P = 0.01; (consecutive PZP applications)2: estimate = −0.51, SE = 0.22, z = −2.33, P = 0.02; age at first PZP application: estimate = 0.10, SE = 0.05, z = 1.84, P = 0.07). Prior research has shown that five to seven years of consecutive PZP treatment can be associated with ovulation failure [4]. The present dataset is consistent with this result, as no mare receiving the vaccine for five or more consecutive years became pregnant.

Bottom Line: Since the contraception program began in January 2000, foaling has occurred over a significantly broader range than it had before the contraception program.In addition, reproductive cycling into the fall months could have long-term effects on foal survivorship.We suggest minor alterations to management strategies to help alleviate such unintended effects in new populations.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America. cmvnunez@princeton.edu

ABSTRACT

Background: 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.

Methodology/principal findings: 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/significance: 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.

Show MeSH
Related in: MedlinePlus