Field testing of single-administration porcine zona pellucida contraceptive vaccines in white-tailed deer (Odocoileus virginianus)

Abstract

Context Many contraceptive agents have demonstrated effectiveness in wild species, most notably immunocontraceptives such as GnRH conjugates and porcine zona pellucida (PZP). The major challenge in using these agents to control deer and other wildlife populations in the field now lies with safe, effective and efficient delivery to a large-enough proportion of the population to suppress growth. Aims Because deer and other wildlife are typically difficult to access for treatment, contraceptives that require multiple or repeated treatments will be of limited management value. To address this constraint, we conducted a field study of white-tailed deer (Odocoileus virginianus) on Fripp Island, SC, USA, to test two different technologies for achieving single-administration, multi-year efficacy in PZP vaccines. Methods Between 2005 and 2010, we captured, ear-tagged and blood-sampled a total of 245 individual adult and yearling female deer. Deer were hand-injected at capture with one of two preparations of SpayVac or a combination native PZP–adjuvant emulsion plus PZP–adjuvant incorporated into lactide–glycolide polymer pellets engineered to release at 1, 3 and 12 months post-treatment. Pregnancy was determined from serum assays of pregnancy-specific protein B sampled from captured deer. Key results Aqueous SpayVac, and the PZP–adjuvant-containing polymer pellets manufactured through a heat extrusion (H/X) method administered simultaneously with PZP–AdjuVac or modified Freund’s complete adjuvant emulsions reduced pregnancy rates from control levels by 95–100% in the first year after treatment, and by 65–70% in the second year after treatment. Conclusions A single, hand-injected vaccination with SpayVac or PZP–adjuvant emulsion combined with H/X PZP pellets reduced fertility for multiple years. Implications Single-treatment, multi-year immunocontraceptive vaccines bring contraceptive management of wildlife populations one step closer. Future efforts should focus on improving handling and storage, developing technologies for remote delivery, and addressing remaining regulatory and management concerns.