Gene therapy shows promise as feline spay alternative

Scientists have developed a promising new gene therapy that some suggest may one day replace surgery as the primary method to sterilize female cats.

A single injection of a feline anti-Müllerian hormone (AMH) transgene was sufficient to induce long-term contraception in female cats, according to a study in the June 6 edition of the online journal Nature Communications.

“This research is a huge leap—we’re really excited about it,” Joyce Briggs, president of the nonprofit Alliance for Contraception in Cats & Dogs, said in a statement. If the technology can be broadened, and include dogs, Briggs said it could make a “huge impact” in the overpopulation of cats and dogs worldwide.

Three kittens sitting outside
A single dose of a feline anti-Müllerian hormone (AMH) transgene prevents ovulation and conception in cats for two years, according to a small-scale study.

Six female cats at the Cincinnati Zoo’s Center for Conservation and Research of Endangered Wildlife (CREW) had the AMH gene therapy injected into their thigh muscles, and three untreated females served as controls. Overall AMH levels in the treated cats increased about 100 times higher than normal, preventing the ovarian follicles from maturing and releasing eggs.

“(W)e show that ectopic expression of anti-Müllerian hormone does not impair sex steroids, nor estrous cycling, but prevents breeding-induced ovulation, resulting in safe and durable contraception in the female domestic cat,” the study states.

To test the effectiveness of the injection, researchers set up two, four-month mating trials with male cats that began eight and 20 months after the treatment. They housed the nine cats in a group with a male that had bred before and recorded video to document mating interactions. In both trials, the three cats in the control group all became pregnant and gave birth to healthy kittens. Of the six cats that received the treatment, two mated with males, but none became pregnant.

Evidence for the effectiveness of the feline AMH gene therapy is strong, Dr. Lindsey Vansandt, lead author of the paper and director of CREW’s Imperiled Cat Signature Project, said in a statement.

The treated cats have been monitored for more than three years to assess the safety of the treatment, including regular physical exams, abdominal ultrasounds, and bloodwork, according to the study report. There were no adverse effects observed in any of the treated cats, suggesting that at the doses tested, the gene therapy was safe and well tolerated.

All of the cats were put up for adoption once the study ended.

A version of this story appears in the September 2023 print issue of JAVMA