Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

Context.: Contraception is increasingly used as a management technique to reduce fertility in wildlife populations; however, the feasibility of contraceptive formulations has been limited until recently because they have required multiple treatments to achieve prolonged infertility.

Aims.: We tested the efficacy and evaluated potential side effects of two contraceptive formulations, a porcine zona pellucida (PZP) formulation, SpayVac® and a gonadotrophin-releasing hormone (GnRH) formulation GonaCon-B™, in a population of free-roaming feral horses (Equus caballus). Both formulations were developed to provide several years of infertility with one injection.

Methods.: Females were treated in June 2005 with either GonaCon-B (n = 24), SpayVac (n = 20), adjuvant only (n = 22), or received no injection (n = 18). Females were monitored for fertility status year round for 3 years after treatment.

Key results.: Both contraceptive treatments significantly reduced fertility for 3 years. Fertility rates for GonaCon-B mares were 39%, 42% and 31%, respectively, and 37%, 50% and 44% for SpayVac mares. During the same seasons, 61%, 67% and 76% of control females were fertile. We found no significant effects from contraceptive treatment on the sex ratio of foals, birthing season or foal survival.

Conclusions.: These results demonstrated that both vaccines are capable of significantly reducing fertility for several years without boosters.

Implications.: Contraceptive vaccines examined in the present study represent a useful tool for the management of feral horses, because of their being efficacious for 3 years in the absence of booster immunisations.

Secondary title Wildlife Research
Author Meeghan E. Gray, David S. Thain, Elissa Z. Cameron and Lowell A. Miller
Date 18/10/2010
Year 2010
Volume 37
Number 6
Pages 475-481
ISBN/ISSN doi:10.1071/WR09175
Control method Fertility Control