Developing a one-time, easy-to-administer, low-cost pill or injection has become the holy grail of feline sterilization. While we’re not quite there yet, we do have a contraceptive option for female cats, and a couple of other experimental sterilization methods in the wings.
iSpay and iNeuter
Epivara was founded by Dr. CheMyong Jay Ko of the College of Veterinary Medicine at University of Illinois Urbana-Champaign. Dr. Ko has been working on using injections of a synthetic estrogen to sterilize a variety of animals, including cats.
iSpay and iNeuter are given under the skin to kittens who are very young and have not developed reproductive organs. This timing prevents sex organs from developing, meaning that the kitten will never be able to reproduce.
Epivara is working on getting the swine version of their product approved for commercial use, so it will probably be a couple of years before we see availability of their feline product. FDA approval takes time so that we can be sure the products are safe and work as intended.
Gene Therapy
In 2023, Vansandt et al published a paper in Nature Communications about using increased anti-Mullerian hormone (AMH) production to prevent ovulation in female cats. The researchers modified genes to increase AMH production and then attached the genes to a virus. This concoction was then injected into the muscle of six female cats.
The cat’s DNA is not altered, but the genes associated with the virus signal the body to produce AMH. As a result, the cats in the study did not ovulate and did not become pregnant. This held for a two-year study period, and the effects may last longer.
Research focused on the use of AMH to sterilize female cats is still ongoing. We don’t fully understand how and why it works yet, and there is a chance that the effects of the injection will wear off over time as muscle cells are regenerated.
Calcium Chloride
Calcium chloride can be mixed with alcohol and injected into a cat’s testicles as a form of chemical castration. This is still considered an experimental method and should be pursued with caution.
The injection causes tissue necrosis, effectively killing the testicles and preventing testosterone and sperm production. But trouble can arise if the injection is given or leaks outside of the testicular capsule. Cats neutered in this manner should be monitored for several days and may require wound care if complications arise.
Megestrol Acetate
Megestrol acetate (MA) is a synthetic progesterone that can be given by mouth to prevent female cats from coming into heat. Alley Cat Allies, a group that does extensive work on managing stray and feral cats, recommends using MA as a temporary stopgap to prevent a female cat from coming in heat and getting pregnant while waiting for a spay appointment. MA is given once a week for up to seven months. It requires a prescription. MA is not ideal for managing feral cat colonies, because you need to be sure that each female cat is getting her correct dose each week—not an easy feat with free-roaming felines.
Bottom Line
Surgical procedures are still the gold standard. Megestrol acetate can be used to prevent young female cats from coming in heat, but it isn’t practical for long-term use or for feral cats. That said, in the future we might have access to cheaper and easier sterilization options.
