Long-term effects of immunocontraception on wild boar fertility, physiology and behaviour

Abstract

Context Fertility control appears as a publicly acceptable alternative to lethal methods for limiting population growth in wildlife. Recently developed single-dose immunocontraceptive vaccines have induced infertility in several mammals. However, the potential side-effects and the long-term effectiveness of these contraceptives have been poorly investigated. Aims We tested the long-term effectiveness and potential side-effects of the single-dose gonadotrophin-releasing hormone (GnRH) vaccine GonaCon™ on captive female wild boar. Methods We carried out two sequential trials: Trial 1 (n = 6 GonaCon™-treated and 6 control wild boar) and Trial 2 which started two years later and replicated Trial 1. We assessed the effectiveness of GonaCon™ to cause infertility by measuring GnRH antibody titres, by monitoring the oestrous cycle through the concentration of faecal progesterone and by recording the sows’ reproductive output in the 4–6 years following treatment. We evaluated the potential side-effects by monitoring behaviour, bodyweight and haematological and biochemical variables. Key results GnRH-antibody titres decreased with time but were still detectable in all females six years after vaccination with a single dose of GonaCon™. In Trial 1 none of the treated females gave birth in the six years after vaccination. In Trial 2, progesterone indicated that two of the six treated females were cycling. One of the cycling treated females gave birth one year after vaccination; the other five, including the second cycling sow, did not reproduce in the four years following vaccination. We found no differences in bodyweight, haematology, biochemistry and behaviour and no obvious sign of injection site reaction. Conclusions GonaCon™ can suppress reproduction in wild boar with no long-term effects on behaviour and physiology. Therefore, GonaCon™ can be regarded as an effective and safe contraceptive for this species. Implications The lack of evidence of adverse effects and the longevity of effect of GonaCon™ suggest that this contraceptive could be now tested in field trials and in contexts where culling of overabundant populations of wild boar is unfeasible, illegal or unacceptable. These instances include urban areas, parks, and management of diseases where culling might cause social perturbation and result in increased disease transmission rates.