Applications of pig zona pellucida immunocontraception to wildlife fertility control

A unique application of pig zona pellucida (PZP) immunocontraception is the control of wildlife populations. A native PZP vaccine has been successfully applied to wild horse and donkey populations. A single annual booster inoculation was capable of maintaining contraception. Seven consecutive years of PZP treatment in wild mares resulted in no detectable debilitating side effects, and reversibility of contraception has been documented among mares treated for up to 4 consecutive years. Long-term treatment (5-7 years) is associated with some ovulation failure and depressed urinary oestrogen concentrations. Complex social behaviours in horses were unaffected by treatment. PZP immunocontraception has also been successfully applied to white-tailed deer, with no detectable changes in ovarian histology after 2 years of treatment. Seventy-four species of captive zoo animals have been treated with the PZP vaccine, with documented success in 27 species, including members of the orders Perissodactyla (Equidae), Artiodactyla (Cervidae, Capridae, Giraffidae, Bovidae), and Carnivora (Ursidae, Mustelidae, Felidae). Immunocytochemistry studies have demonstrated a high degree of crossreactivity between anti-PZP antibodies and African elephant zona pellucida. The need for a one-inoculation form of the vaccine has led to the incorporation of PZP into lactide-glycolide microspheres, which cause a delayed release of the PZP. PZP immunocontraception of wildlife has potential because of (1) > 90% effectiveness, (2) the ability for remote delivery, via darts, (3) reversibility after short-term use, (4) a wide breadth of effectiveness across many species, (5) a lack of debilitating side-effects even after long-term treatment, and (6) minimal effects upon social behaviours.