Earlier today, we reported on some good news in the development of temporary male birth control, and now we have more good news for dogs, cats, and amorous mice: A new shot could render them sterile, semi-permanently.

With 7.6 million homeless dogs and cats entering shelters every year, scientists and activists have been looking for a cheap, non-invasive birth control method for years. Despite the heartwarming last scene of Lady and the Tramp, constant cycles of puppies and kittens actually spell plenty of suffering for cats and dogs. An organization called Found Animals even offers a $25 million prize to the first person or team that develops a safe, nonsurgical spay or neuter option that works for dogs and cats. (There is one shot that works only on male dogs, ages three- to ten-months old). 

The new injection, which so far has only been tested on mice, essentially contains a piece of DNA that looks like a virus to the mouse's insides. The mouse's muscles reflexively start fighting off the invader by producing antibodies, and those antibodies also happen to stop his or her body from making hormones that stimulate egg and sperm production. No hormones, no eggs or sperm, no babies. 

Right now, it takes about two months from the time of injection to completely sterilize the animal, but researchers are working on shortening that waiting period. And they are hopeful that the shot could last up to ten years, which would cover almost any cat or dog's reproductive years.

One downside is that, by inhibiting hormones, the shot could cause various side effects, including modifying behavior. This is one reason why women regularly switch birth control methods due to side effects. So if the shot were to be developed as a long-term birth control option for women, or for wild species whose behaviors are critical to their ecosystem, more study would be needed.

The next step will be seeing whether the injection works on animals other than mice.

"The challenge is always moving between species," William Swanson, director of animal research at the Cincinnati Zoo and Botanical Garden in Ohio, in a press release.

If that doesn't work, they will tweak their findings to target other molecules that might behave similarly to the ones targeted by the current injection. 

The only sterilizing shot on the market today costs around $20 per animal.

Source: American Association for the Advancement of Science