In the future, the human population has been growing exponentially, while many of the animal populations have been on the decline. In order to try and solve both problems, the governments of the world have banded together to create a new initiative for re-populating animals.
A special serum was created that could transform humans into animals. Its mostly a volunteer effort, but its often offered as an alternative to prison time or military service.
The only complication is the process is permanent, and volunteers tend to be in short supply, so the government is trying to offer more incentives to volunteer such as paying the families or giving volunteers the life of luxury until the problem can be undone, if ever.
Animal options are pretty much endless, as long as DNA can be accessed. Transformed humans will maintain their human memories and can communicate with each other.