Reimmunization increases contraceptive effectiveness of gonadotropin-releasing hormone vaccine (GonaCon-Equine) in free-ranging horses (Equus caballus): Limitations and side effects

Abstract

Wildlife and humans are increasingly competing for resources worldwide, and a diverse, innovative, and effective set of management tools is needed. Controlling abundance of wildlife species that are simultaneously protected, abundant, competitive for resources, and in conflict with some stakeholders but beloved by others, is a daunting challenge. Free-ranging horses (Equus caballus) present such a conundrum and managers struggle for effective tools for regulating their abundance. Controlling reproduction of female horses presents a potential alternative. During 2009–2017, we determined the long-term effectiveness of GnRH vaccine (GonaCon-Equine) both as a single immunization and subsequent reimmunization on reproduction and side effects in free-ranging horses. At a scheduled management roundup in 2009, we randomly assigned 57 adult mares to either a GonaCon-Equine treatment group (n = 29) or a saline control group (n = 28). In a second roundup in 2013, we administered a booster vaccination to these same mares. We used annual ground observations to estimate foaling proportions, social behaviors, body condition, and injection site reactions. We found this vaccine to be safe for pregnant females and neonates, with no overt deleterious behavioral side effects during the breeding season. The proportion of treated mares that foaled following a single vaccination was lower than that for control mares for the second (P = 0.03) and third (P = 0.08) post-treatment foaling seasons but was similar (P = 0.67) to untreated mares for the fourth season, demonstrating reversibility of the primary vaccine treatment. After two vaccinations, however, the proportion of females giving birth was lower (P <0.001) than that for control mares for three consecutive years and ranged from 0.0–0.16. The only detectable adverse side effect of vaccination was intramuscular swelling at the vaccination site. Regardless of vaccine treatment (primary/secondary), approximately 62% (34/55) of immunized mares revealed a visible reaction at the vaccine injection site. However, none of these mares displayed any evidence of lameness, altered gait or abnormal range of movement throughout the 8 years they were observed in this study. Our research suggests that practical application of this vaccine in feral horses will require an initial inoculation that may provide only modest suppression of fertility followed by reimmunization that together could result in greater reduction in population growth rates over time.

Active vaccination against interleukin‐5 as long‐term treatment for insect‐bite hypersensitivity in horses

“…The most prominent therapeutic vaccine in veterinary use is the anti‐boar vaccine Improvac ® , targeting gonadotropin‐releasing hormone (GnRH) . A similar immunocontraceptive vaccine was developed for horses, known as GonaCon‐Equine™, registered in the US for female wild/feral horses and burros. For human use, a number of anti‐self vaccines are in preclinical and clinical development mostly targeting cytokines in inflammatory conditions and personalized anti‐cancer vaccines …”

Phage constructs targeting gonadotropin-releasing hormone for fertility control: evaluation in cats

“…[22][23][24] GonaCon was also described to produce wide interspecies variability in GnRH antibody production. 10,[24][25][26] Phage-GnRH immunizations triggered significant changes in several reproductive parameters. In groups 1 and 2, the group mean of morphologically normal sperm declined at multiple post-immunization time Figure 4 Total testicular volume in cats immunized with phage-gonadotropin-releasing hormone.…”

“…22–24 GonaCon was also described to produce wide interspecies variability in GnRH antibody production. 10,24–26…”

Short Term Safety, Immunogenicity, and Reproductive Effects of Combined Vaccination With Anti-GnRH (Gonacon) and Rabies Vaccines in Female Feral Cats

“…This immunocontraceptive vaccine was designed to trigger the production of antibodies that neutralize GnRH. It has been tested in many species, including white-tail deer (22), elk (23), horses (24,25), cattle (26), ferrets (27), domestic, and wild pigs (28), as well as to a limited extent in dogs (29) and cats (30)(31)(32)(33). However, none of the four previous studies conducted on cats included measurements of rabies antibodies in Gonacon-vaccinated cats, even in the studies in which cats were vaccinated with both vaccines (32,33).…”