Single dose contraceptives that do not require surgery have been effective in six female cats for at least 3 years and are expected to remain effective for the rest of their lives. Injectable contraceptives could then replace surgery as a means of preventing pregnancy in cats.
It would also be the first non-surgical permanent contraceptive for animals. “If this is really a lifetime contraceptive, it will be the first lifetime contraceptive that I know of,” says William Swanson of the Cincinnati Zoo and Botanical Garden in Ohio, who helped develop it.
The technology could probably be applied to other mammals, including humans.
Developing a single-dose permanent contraceptive is a goal pursued by many researchers to control populations without killing animals, especially feral, wild, and invasive animals. Many products already exist that provide long-term contraception in some species.
For example, some wild horses in the United States are given a vaccine called PZP, which induces an immune response in females and prevents pregnancy. However, repeated dosing is required.
For cats, the only permanent way to prevent a female from having kittens is spaying. This is an expensive surgery in which the ovaries, or ovaries and uterus are removed under anesthesia.
Swanson and his team instead developed an approach that involved a single injection into the cat’s thigh muscle.Injection contains DNA It encodes a protein called anti-Müllerian hormone. The DNA is carried by the virus and delivered to the nucleus of muscle cells, where it remains indefinitely.
Mammals naturally produce anti-Müllerian hormone, but injections raise levels in female cats 100- to 1,000-fold higher than normal, preventing follicle development in the ovaries, Swanson said.
In the study, 6 female cats were given contraceptive injections and 3 cats were given dummy injections. Each cat was housed twice for her 4 months with a male cat of proven fertility. All untreated cats became pregnant, but contraceptive cats did not. “The cats are perfectly healthy. We haven’t seen any ill effects,” Swanson says.
Muscle cells persist for life, and cells with the added genes should continue to produce hormones all that time, Swanson said. “That’s why we target muscle.”
Strictly speaking, this isn’t sterilization, he says, and lowering hormone levels will restore fertility.
Different species have different versions of the anti-Müllerian hormone, so injections will only work if they are modified to incorporate the gene for that hormone. This has safety benefits and should not affect fertility if someone accidentally pricks the body with the needle while injecting the cat.
Swanson’s team is funded by a foundation founded by billionaire surgeon Gary Michelson, which calls it “a low-cost, permanent, non-surgical treatment for male and female cats and dogs.” It offers a $25 million bounty for “massive sterilization agents”. The purpose of the award is to reduce the number of companion animals that are euthanized in shelters.
Aim Johnson, a professor at Auburn University in Alabama, said: “Wildlife surgery, in particular, involves a great deal of stress and expense, including capturing an animal, moving it to a surgical facility, operating on it, holding it overnight, and then releasing it. ” says. “A simple injection allows capture, injection, and immediate release.”
However, the feral animal sterilization approach known as trap-neuter-return (TNR) is controversial.
“The problem with TNR is not prevented by the use of injectable contraceptives. , and face the possibility of starvation,” said Patricia Fleming. Murdoch University, Perth, Australia. “Wildlife impacts will continue.”
But contraceptive injections would have less of an impact on animal welfare than spaying, Fleming said.
However, the Michelson Award has so far remained unclaimed. The methods Swanson and his team have developed won’t work for men, so they won’t win.