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 GonaConÔ on captive female wild boar.Methods. We carried out two sequential trials: Trial 1 (n = 6 GonaConÔ-treated and 6 control wild boar) and Trial 2 which started two years later and replicated Trial 1. We assessed the effectiveness of GonaConÔ 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 GonaConÔ. 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. GonaConÔ can suppress reproduction in wild boar with no long-term effects on behaviour and physiology. Therefore, GonaConÔ 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 GonaConÔ 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.

Effects of a GnRH vaccine on the movement and activity of free-living wild boar (Sus scrofa)

“…We confirmed that free-living wild boar responded to GonaConÔ by producing GnRH antibodies at levels that are known to be associated with infertility in captive wild boar and feral pigs (Miller et al 2003;Killian et al 2006;Massei et al 2008Massei et al , 2012. It also appeared that, as previously found in bison (Miller et al 2004), GonaConÔ vaccination did not affect existing pregnancy.…”

“…Efficacy of a similar treatment in captive mares (Equus caballus) declined from 94% to 40% over 4 years, (Killian et al 2008b), and efficacy was lower for feral mares taken from the same population ), although fertility rates of treated animals were still significantly lower than those of controls. Compared with the results obtained with captive wild boar animals, where some sows were rendered infertile for at least 6 years, infertility in the treated free-living animals might not have lasted as long; titres in female F15 had dropped to 1 : 32 000 after 18 months, a level that in captive wild boar was associated with returning fertility (Massei et al 2012). The declining pattern of antibody titres observed in that animal suggested that infertility much beyond 72 weeks would have been unlikely, although in captive wild boar, antibody titres declined over the first 12-24 months post-injection, then remained at a sufficient (low) level to block reproduction for several years (Massei et al 2012).…”

“…2). Two treated sows resampled at 54 weeks had GnRH antibodies detectable at 1 : 32 000-1 : 12 8000 dilution; hence, one or both of these were likely to be infertile; in a previous study on captive wild boar, one of two females with a titre of 1 : 32 000 dilution did not reproduce (Massei et al 2012). One of the two treated sows resampled at 54 weeks was resampled again at 72 weeks; GnRH antibody titres were detected at 1 : 32 000 dilution, suggesting that this animal may still have been infertile at that time.…”

“…We set traps with the aim of sampling the population every 2 weeks, and prebaited traps during the intervening weeks. The enzyme-linked immunosorbent assay (ELISA; NWRC, Fort Collins, CO, USA) was used to measure anti-GnRH antibody titres, following the method of Massei et al (2012).…”

“…No differences in space-use patterns and fidelity to seasonal breeding ranges were observed in ovariectomised brushtail possums (Trichosurus vulpecula) (Ramsey 2007) or surgically sterilised vixens (Vulpes vulpes) (Saunders et al 2002). The longterm effectiveness and potential side effects of GonaConÔ were recently evaluated in captive female wild boar (Massei et al 2012); 11 of 12 females did not give birth for at least 4 years (and some for 6 years) post-vaccination, but no effects were seen on bodyweight, haematology, biochemistry and on the social ranking of females that were housed together (there were no apparent ill effects of the vaccine on the single treated sow that did give birth or her piglets). However, there have been very few studies of the effect of contraceptive vaccines on the physiology and behaviour of free-living animals.…”