Effectiveness, Reversibility, and Serum Antibody Titers Associated with Immunocontraception in Captive White-Tailed Deer

Abstract

Because immunocontraception may have management application for white-tailed deer populations in parks and preserves where hunting is illegal or impractical, we examined physiological aspects of immunocontraception with porcine zonae pellucidae (PZP) in fertile white-tailed does (Odocoileus virginianus). In 4 experiments, we examined the effectiveness of 3- and 2-PZP injections for controlling fertility of does, as well as 2 protocols using 1 injection. We used sample sizes of 5, 8, 6, and 7 does for PZP treatment and 8, 6, 6, and 7 does for controls in the experiments. We administered a single PZP booster inoculation after 1 year to all does used in the 3-injection experiment. Each 1-injection vaccination consisted of 1 dose of PZP as in other protocols plus a second controlled-release dose of PZP delivered via an osmotic mini-pump implant or injected biodegradable polymer microspheres. We monitored fawn production for 1-3 years in all does and measured serum anti-PZP antibody titers at various times post treatment in 15 randomly selected PZP-treated does and in 2 control does. Except for 2 of 7 does given 1 injection containing microspheres, none of the PZP-treated does in any experiment produced fawns the first year after treatment. In 49 possible breeding periods among control does (placebo = 8, untreated = 41) the pooled incidence of fawn production was 93.8%. Fawn production among 8 monitored does (2- and 3-injection protocols) was 75% 2 years after treatment was discontinued, demonstrating reversibility of treatment. Serum anti-PZP antibody titers (17 does tested) were present only after PZP treatment, and highest titers occurred in does given 2 or 3 separate PZP injections. Regardless of protocol, PZP-treated does with >50% of maximal antibody titers at the onset of a breeding season did not produce fawns, whereas does with 50% of maximal after 32-40 weeks. Our data demonstrate in white-tailed does that PZP vaccination: (1) can produce contraception for at least 1 breeding season, (2) yields greater efficacy with multiple injections than with 1 injection, (3) is reversible within 2 years in 75% of does, (4) is associated with elevated anti-PZP antibody titers, and (5) can produce a sustained antibody response through at least 1 breeding season. The titer data suggest that PZP vaccine in white-tailed deer behaves in a manner physiologically similar to PZP vaccine effects reported in several other species. The fawn count data indicate that PZP vaccine has potential management application for white-tailed deer.