Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.
PLoS One. 2010 Oct 26;5(10):e13635. doi: 10.1371/journal.pone.0013635.
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.
尽管已对猪卵透明带（PZP）免疫避孕的生理效应进行了充分研究，但对 PZP 对生殖周期安排的影响知之甚少。最近的行为研究表明，接受 PZP 处理的受者将发情配种期延长到了通常的非繁殖季节。
方法/主要发现：为了确定是否如此，我们整理了北卡罗来纳州沙克尔福德银行（Shackleford Banks）的野马（Equus caballus）的产驹数据，这些马在接受 PZP 避孕管理前进行了 4 年（避孕前，45 匹母马共 65 匹驹；避孕后，46 匹母马共 97 匹驹），并在避孕管理后进行了 8 年的监测。在野马中，妊娠期约为 11-12 个月，这意味着受孕大约在产驹前 11.5 个月。自 2000 年 1 月避孕计划开始以来，产驹的时间范围明显比避孕计划开始前更广。接受 PZP 处理的母马（27 匹母马共 45 匹驹）的产驹时间一直比未接受处理的母马（19 匹母马共 52 匹驹）的产驹时间更广泛。此外，当前接受 PZP 处理的母马产驹的时间比以前接受处理和未接受处理的母马晚。连续接受更多 PZP 处理的母马在季节后期产驹，而接受较少处理的母马则较早产驹。最后，PZP 的效果随着连续应用次数的增加而下降，在连续应用 5 次后达到 100%。
结论/意义：对于马等群居物种，生殖周期延长到秋季会产生重要的社会后果，包括群体稳定性下降和雄性生殖行为延长。此外，生殖周期延长到秋季可能对幼驹的存活率产生长期影响。在新种群中实施免疫避孕计划之前，管理人员应考虑这些因素。我们建议对管理策略进行轻微调整，以帮助减轻新种群中出现的此类意外影响。
