SAN FRANCISCO, California (Reuters) -- California may become the only U.S. state to require the sterilization of pets under a bill passed by the state Assembly, pitting dog and cat lovers against animal rights activists. "It's a horrific bill," said Maureen Hill-Hauch, executive director of Castleton, New York-based American Dog Owners Association, adding that enforcement of the bill in theory could wipe out California's dog population. The bill would require pet owners to spay and neuter their dogs and cats, or face a $500 fine for each animal.