Non-lethal management methods are required for wild equids that are protected
by law and for deer inhabiting areas where lethal controls are not legal or
safe. Single or multiple inoculations of porcine zona pellucida (PZP) vaccine
have been delivered to wild horses and deer by means of darts. Contraceptive
efficacy in horses after two inoculations ranged from 90% to
100%, and after a single inoculation ranged from 19% to
28%. Mares given a controlled-release form of the vaccine had foaling
rates ranging from 7% to 20%. No detectable changes in social
organization or behaviours among treated horses occurred. Contraceptive
effects were reversible after 4 consecutive years of treatment but 5–7
years of treatment resulted in ovulation failure and decreased urinary
oestrogen concentrations. Among deer, two inoculations were
70–100% effective in preventing fawns, but one inoculation
yielded a contraceptive efficacy of ≤20%, with pregnancies occurring
late in the breeding season; a single annual booster inoculation reduced
fertility to 20% in the second year. Energy costs of extended breeding
seasons were less than those resulting from pregnancy. After two years of
treatment, ovaries appeared normal. These studies suggest that PZP
immunocontraception can be successfully applied to certain free-roaming
populations of wild horses and deer.
