Research articleLong-term fertility control in female cats with GonaCon™, a GnRH immunocontraceptive
Introduction
Unowned free-roaming (feral) cats number in the millions nationally and exist throughout the world [1]. Their uncontrolled reproduction contributes to cat overpopulation and associated concerns regarding their impact on public health and the environment [2]. In parts of the world where progressive animal control resources are not available, measures such as poisoning and shooting are still used to control cats [3]. Surgical sterilization followed by return to the colony is an increasingly popular method of controlling feral cat populations, but is expensive, labor-intensive, highly technical, and limited in scale [4], [5].
Nonsurgical fertility control that could be administered to feral cats in the field would be a powerful tool for cat population control. Control of free-roaming species is often aimed at the level of the population, rather than at specific individual animals. Treatment must be efficacious in a high proportion of the population, but it is not essential that every treated animal be rendered infertile. Feral cats are wary of humans, and once trapped and released, are unlikely to return for repeated trapping episodes. A practical fertility control technique for feral cats would induce permanent or multi-year duration of action following a single treatment in the majority of animals treated.
Vaccines aimed at reproductive targets are one approach to nonlethal control of overabundant free-roaming species. Overcoming tolerance to self antigens and induction of durable immunity without the use of repeated booster vaccines are substantial challenges for the development of immunocontraceptive vaccines. A commonly used contraceptive antigen in wildlife is the zona pellucida. In previous studies, we demonstrated that vaccinating against the zona pellucida was ineffective in preventing pregnancy in cats [6], [7]. Subsequently, we showed in a short-term study that a single dose of GnRH vaccine in a mycobacterial and oil emulsion (GonaCon™) effectively blocked testosterone production and spermatogenesis for at least 6 mo in a majority of vaccinated adult male cats [8]. This was apparently the first report to suggest that fertility control may be achievable in cats following a single vaccination against a reproductive self antigen.
We hypothesized that long-term fertility control in cats can be induced by immunological blockade of GnRH activity. The purpose of this study was to test the efficacy and duration of activity of single-dose GnRH immunocontraception on the fertility of adult female cats.
Section snippets
Cats
Twenty-four 8- to 14-mo-old specific-pathogen-free female domestic shorthair cats were acquired from a commercial vendor (Liberty Research, Waverly, NY, USA). Cats were group-housed in one large enriched room with raised resting benches, maintained at ambient temperatures between 21 and 23 °C, and exposed to controlled lighting (explained later). Food and water were available ad libitum. The experimental design was approved by the University of Florida Institutional Animal Care and Use
Reactions to treatment
Body temperature in all of the cats remained normal after treatment, and there was no inflammation or tenderness at the injection sites. One vaccinated cat died suddenly 45 d after treatment; necropsy revealed no gross or histological abnormalities to explain the death. This cat was replaced with a 2 y old cat of proven fertility from the colony and vaccinated with the GnRH vaccine according to the standard protocol.
Twenty-four months after immunization, it was discovered that one of the cats
Discussion
The vaccine used in this study induced fertility control in 100% of cats following a single injection, but duration of contraception varied from 5 mo to > 5 y. Infertility was maintained for 3 y in approximately half of the cats and for more than 5 y in a quarter of the cats. Response to vaccination was accompanied by a cessation in estrous cyclicity and with weight gain, similar to cats undergoing surgical sterilization via ovariectomy.
This is apparently the first study to demonstrate
Acknowledgments
Supported by a grant from the Morris Animal Foundation.
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