Scientists Develop New Birth Control for Female Cats—No Surgery Necessary

The one-time injection of a gene therapy could eventually be used to control cat populations

Two orange kittens look at the camera
Researchers hope that an injection could one day be a faster and safer substitute for surgical cat sterilization. Christopher Furlong via Getty Images

Researchers have developed a permanent birth control for female cats that would mean the animals don’t have to undergo invasive surgery to be spayed, according to a new study. The single injection could aid the effort to control cat numbers globally.

The world cat population has reached an estimated 600 million, and roughly 80 percent of them are free-roaming. These natural hunters cause a lot of harm to wildlife: In the United States alone, domestic cats kill between 1.3 billion and 4 billion birds and between 6.3 billion and 22.3 billion mammals each year. Currently, the main method for sterilizing cats involves surgery—a costly and risky procedure.

The new technique, described in a paper published Tuesday in the journal Nature Communications, involves a one-time injection of a gene therapy that could provide long-term birth control for female cats. The preliminary study was small and involved only nine felines, six of which received the treatment. Later this year, researchers will meet with the Food and Drug Administration to discuss how to further test their method, David Pépin, a co-author of the new study and molecular biologist at Harvard Medical School, tells Inverse’s Elana Spivack.

“This is really exciting, and I hope it will pan out,” Julie Levy, a veterinarian at the University of Florida who did not contribute to the research, tells the New York Times Alla Katsnelson. “Wouldn’t it be great if we could send out a technician into the field to inject cats and then let them go?”

Today, the surgery for neutering cats requires removing their reproductive organs. This invasive operation increases the animal’s risk of infection and hemorrhaging and takes seven to ten days to recover from.

“Surgery, especially in feral animals, has extensive stress and cost involved in trapping the animals, relocating them to a surgery facility, doing the surgery, holding them overnight and then releasing them,” Aime Johnson, a veterinarian at Auburn University who wasn’t involved in the research, tells New Scientist’s Michael Le Page. “A simple injection would allow trapping, injection and release immediately.”

Since the surgery must be done by experts, veterinarian availability also limits how much progress can be made.

“We needed a way to get the highly trained surgeon out of the picture and allow a layperson to be able to give an injection that prevents cats from reproducing,” William Swanson, a co-author of the study and wildlife veterinarian at the Cincinnati Zoo, tells National Geographic’s Connie Chang.

Overcrowded shelters have also led to higher euthanization rates, Levy tells the Atlantic’s Katherine J. Wu.

In the study, female cats were injected in their thigh muscle. The shot delivers a viral cell—with the parts that cause sickness removed—and within the cell is genetic material. The DNA tells the cat’s muscles to create a protein called the anti-Müllerian hormone, until it reaches 100 to 1,000 times the normal level, per New Scientist. This appears to stop the ovaries from maturing and releasing eggs.

To test whether the injection was effective, the 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, per the New York Times, but none became pregnant.

“This really could be game changing, if we can get it to work as well as we hope,” Swanson tells National Geographic.

Still, Daniela Chavez, a cat reproduction biologist at Towson University who wasn’t involved in the research, tells the Atlantic that the findings should be considered “really preliminary.” Further research—with larger groups of cats—will be needed to confirm whether the treatment is safe, how long it lasts and how effective it truly is.

Get the latest stories in your inbox every weekday.