LOS ANGELES (AP) — Mayor Antonio Villaraigosa on Tuesday signed one of the nation's toughest laws on pet sterilization, requiring most dogs and cats to be spayed or neutered by the time they are 4 months old.

The ordinance is aimed at reducing and eventually eliminating the thousands of euthanizations conducted in Los Angeles' animal shelters every year.

The ordinance does exempt some animals, including those that have competed in shows or sporting competitions, guide dogs, animals used by police agencies and those belonging to professional breeders.