Meeting Abstract
Due to the extirpation of their natural predators, feral horse populations have expanded across the United States, necessitating their management. Contraception of females (mares) with porcine zona pellucida (PZP) is a popular option; however, effects to physiology and behavior can be substantial. For example, on Shackleford Banks, North Carolina, USA, treated mares have extended ovulatory cycling into the non-breeding season, resulting in later foaling dates, and have demonstrated decreased fidelity to the band stallion, changing social groups more frequently. However, PZP’s long-term effects on mare physiology and behavior remain largely unexplored. After the contraception program was largely suspended on Shackleford Banks in 2009, we examined how prior exposure to varying levels of PZP treatment impacted 1) foaling probability and foaling dates from 2009-2014 and 2) mare fidelity to the band stallion during 2013 and 2015. Mares receiving any level of prior PZP treatment were less likely to foal than were untreated mares. Additionally, previously treated mares continued to give birth later than did untreated mares. Finally, mares previously receiving 4 or more treatments continued to change groups more often than did untreated mares, while mares previously receiving 1-3 treatments did not. Our results suggest that although PZP-induced infertility and its associated behavioral effects can persist after the cessation of treatment, these effects can be ameliorated for some factors. Careful consideration to the frequency of contraceptive treatment is important to maintaining more natural physiological and behavioral functioning in wildlife populations.
