Updates from the 5th International Symposium on Non-Surgical Methods of Pet Population Control

by Zarah Hedge, DVM, MPH

Dr. Zarah Hedge (l) training veterinary professionals at a Zeuterin™ certificate training session at the ACC&D symposium in July.
Alliance for Contraception in Cats and Dogs

August 26, 2013

The development of a non-surgical method of sterilization for the management of dog and cat populations has long been the dream of many working in the animal welfare field, including myself. As a shelter veterinarian familiar with resource challenges and overpopulation problems, I know that surgical sterilization -- while an effective means of population control -- is not always practical, especially in impoverished areas, nor is it always possible to spay and neuter a large enough portion of a population to cause a decline. Non-surgical methods of sterilization offer an alternative method to population control that have the potential to be less invasive, faster to administer, and more feasible.

The Alliance for Contraception in Cats and Dogs was founded in 2000 with a mission to “expedite the successful introduction of methods to non-surgically sterilize dogs and cats and to support the distribution and promotion of these products to humanely control cat and dog populations worldwide.”

This June, I attended ACC&D’s 5th International Symposium on Non-Surgical Methods of Pet Population Control in Portland, Ore. The symposium drew in over 150 attendees and 65 speakers from six continents and 16 countries, including researchers, veterinarians, and animal welfare professionals. The symposium included general discussions on what would make an ideal sterilant or contraceptive, ethical considerations with population management, and discussions on current non-surgical methods with the potential for near-term impact. The Field Implementation Track dealt with actual implementation of various methods, and a Sterilant/Contraceptive Discovery Track dealt with current research on existing and new potential methods of non-surgical sterilization.

Non-surgical methods: Chemical castration

Several non-surgical methods exist, some of which have received regulatory approval or are undergoing field trials. Chemical castration targets the destruction of gonadal cells in males causing infertility by azoospermia, or lack of sperm production. This approach has been studied for nearly 50 years, and FDA approval has been given to Zeuterin™, developed by Ark Sciences, for use in male dogs. Zeuterin™ (known internationally as EsteriSol™) is a zinc gluconate compound buffered with arginine which causes testicular atrophy, seminiferous tubule collapse, and intra-testicular scar tissue formation. Only one inexpensive intratesticular injection is necessary for irreversible sterility and 40-50% testosterone reduction. The current formulation requires training and certification to administer, which optimizes efficacy while minimizing adverse effects. Current research is aimed at examining the testosterone levels over time as well as behavior analyses of both chemically castrated versus surgically castrated dogs. Age and testicular size limitations are also being addressed in research.

Other methods targeting gonadal tissues discussed at the Symposium include intratesticular injection of calcium chloride, as well as a molecule known as KU-AS-272, which early research has found to be effective in sterilizing rats when given as a single dose subcutaneous injection.

Non-surgical methods: Immunocontraceptives

Immunocontraceptives are another type of non-surgical method that has been researched for decades. These methods utilize the immune system to attack specific cells involved with reproduction. One such vaccine targets gonadotropin-releasing hormone, or GnRH (hypothalamus), causing the body to produce antibodies that inhibit its activity, leading to suppression of LH and FSH release (pituitary) and estrogen and testosterone production, rendering the animal infertile. The USDA has an-EPA approved GnRH-targeted vaccine (GonaCon), which has been used in deer and wild horse herds. Research is being done to develop canine and feline specific formulations of GonaCon that would reduce the incidence of local injection-site reactions and that would provide a long lasting immune response, two issues that researchers have been working to find solutions to for several years. Studies examining novel GnRH-targeted vaccines are underway, including the use of attenuated feline herpesvirus-1 (FHV-1) vector for feline GnRH vaccines, which is known to cause a strong and long lasting immune response, as well as the use of a filamentous phage as a carrier for contraceptive vaccines. Research on the concomitant administration of a GonaCon-Canine formulation with rabies vaccination found no adverse effects, which could have important implications for future rabies and population control programs.

Other new non-surgical sterilization methods in development

Other promising non-surgical contraceptive methods are GnRH agonists, which cause a down-regulation of GnRH and suppression of reproductive hormones in both males and females, leading to sterility. Superlorin®, a subcutaneous implant, has been used in zoo animals for many years. While it has variable efficacy duration of one to several years, it may be a beneficial tool for managing stray dog and cat populations. Current research is aimed at examining the optimal dosages for dogs and cats and the time of implant to achieve the maximum length of contraception. Exciting novel approaches to non-surgical sterilization were also shared at the symposium. Research focusing on gene silencing to target and silence molecules vital to fertility and induce permanent sterility are in the early stages, as is research aimed at the development of targeted GnRH cytotoxins that would destroy cells with GnRH receptors thus rendering the animal sterile. Many studies discussed at the symposium were funded by grants from the Michelson Prize & Grants in Reproductive Biology, which has awarded funding for 25 proposed studies on non-surgical methods of sterilization and contraception to date.

Field Implementation

In the Field Implementation Track, speakers discussed population dynamics of free roaming cats and dogs, sharing simulation models evaluating various methods of population control, including both non-surgical and surgical sterilization. They also discussed ideas for marking and identifying sterilized animals in free-roaming settings and shared lessons learned from field studies thus far. Julie Levy, DVM, Ph.D, from the Maddie’s Shelter Medicine Program at the University of Florida,discussed the ethical considerations of performing field trials in disadvantaged regions, including a discussion on standards of care for field research and implementation of non-surgical sterilization methods. These ethical considerations were highlighted several times throughout the symposium, and it was inspiring to see this very poignant topic addressed repeatedly at a scientific seminar.

Looking to the Future

The symposium brought together a wide range of individuals from various aspects of the animal welfare field and scientific community, all of whom have a strong interest in the development of humane non-surgical methods of management and control for free-roaming dog and cat populations. Attendees agreed that the event allowed for a good exchange of ideas and the chance for future successful collaboration. It was highly educational and inspiring for me to learn about the various non-surgical tools being researched and implemented in the field. As a shelter veterinarian who is passionate about free roaming dog and cat population management, I hope to continue utilizing Zeuterin™ in the field to help sterilize animals both in the US and abroad, as well as apply other methods as they become available. I also hope to take part on future projects that help develop and test new methods of non-surgical contraception.

While there are currently two non-surgical contraception products on the market (Zeuterin™/EsteriSol™ and Superlorin®), it will likely be several years before a single-dose contraceptive for both cats and dogs is developed and made available. However, there is innovative research on the horizon and I have no doubts we will achieve the goal of developing effective, safe, affordable, permanent methods of contraception for both male and female dogs and cats within my lifetime.

For more information on the 5th International Symposium on non-Surgical Contraceptive Methods of Pet Population Control, including the entire symposium proceedings, visit the ACC&D website. There is also a free e-book fertility control in dogs and cats you can download for more information on this topic.

Dr. Zarah Hedge graduated from Western University of Health Sciences in 2009 and recently completed a three-year shelter medicine residency program at the Oregon Humane Society (a program she helped design). Dr. Hedge is now working as a shelter veterinarian at the San Diego Humane Society and SPCA. She also recently received her Master’s in Public Health from the University of Minnesota. During her shelter residency, Dr. Hedge performed over 8,000 dog, cat and rabbit spay/neuter surgeries as well as other surgical procedures ranging from soft tissue surgery to orthopedic and dental procedures in canine, feline, small mammal and avian patients. Dr. Hedge is a member of the HSVMA Leadership Council.