This law does not pertain to FERAL cats/dogs. It does apply to killing the household PETS that belong to other people.
I would put that number much lower. Our barn cats average less than two.There are volunteer groups in almost every county who trap feral cats. Then their fixed and released. Most wild cats live only 6 or 7 years. They are easy prey around here for foxes and coyotes. Also cars.
I'm not saying their not a pest, but there is humane ways to deal with them.