State lawmakers are looking at a bill that would require pet retailers in Hawaii to sterilize all cats and dogs before selling them.

Passing such a law would lessen the suffering of feral cats because of overpopulation and reduce the number of animals euthanized in shelters, said Inga Gibson, state director of the Humane Society of the United States. Many feral cats are the offspring of abandoned house cats that haven’t been sterilized, she added.

House Bill 243 notes that an unsterilized female cat can give birth to two litters a year, which, extrapolated over seven years, could lead to 400,000 cats.

Feral cat colonies continue to grow despite various efforts to control the cat population, and the pressures of overpopulation lead to starvation of the weakest and the spread of disease and mange, a form of animal cruelty when uncontrolled, the bill says.

"It’s a tremendous issue," Gibson said. "We have a large feral cat issue throughout the state. One of the contributing factors is the sale of unsterilized cats."

Feral cats are also a threat to Hawaii’s endangered birds, according to the state Division of Forestry and Wildlife.

The bill is just one version of animal cruelty legislation that is heading to a conference committee to work out differences between House and Senate versions.

State laws mandating the spaying or neutering of dogs or cats appear to be rare. At least one state, Rhode Island, mandates it if the animals are released from a shelter. Some counties on the mainland, however, completely ban the sale of cats or dogs, while a Los Angeles ordinance from 2008 requires pet owners to sterilize their dogs or cats by the age of 4 months.

Despite the large feral cat population, the Humane Society opposes euthanasia and supports managed cat colonies for unsocialized cats, where a caretaker will get the animals sterilized, microchipped, vaccinated, fed and looked after.

"It’s not an easy life for a cat that’s not part of a managed colony," Gibson said.

Theresa Donnelly, who breeds boxers and is secretary of the Boxer Club of Hawaii, said the bill wouldn’t affect purebred dogs because hobby breeders usually sell person to person, which is not regulated by the bill.

"Any reputable breeder would never sell to a pet store anyway," she said. Hobby breeders want to meet potential owners to make sure their dogs will have a safe home and possibly establish a relationship with the new owners to promote ethical breeding, she said. "People who want to breed animals should be mentored."

Tish Rothwell, owner of the Pet Depot in Ewa Beach, said her business has been fixing cats before adopting them out ever since hundreds of animals were rescued from a Waianae no-kill shelter when the owner died in July 2009.

After the rescue, shelters were full and couldn’t take animals from people who were trying to give up their pets. Rather than see cats euthanized in shelters, Rothwell’s store took the animals and sterilized them before adopting them out for a fee that covered medical costs.

"We want to be responsible and keep that out-of-control cat population down," Rothwell said.

However, she has concerns about mandating the fixing of dogs. They recover slower than cats after being spayed or neutered and require more care, raising the cost of the animals.

Brent Chung, manager of Kalihi Pet Center, said some customers may not mind if the bill becomes law, but pet stores may require breeders to have dogs fixed before selling them to the retailer, reducing the supply of dogs in stores. He said some veterinarians are backlogged and the dogs may be months old by the time an animal can be sterilized, frustrating customers that want dogs as young as 6 weeks old that are easier to train. He suspected the bill could also boost sales of unsterilized dogs outside of stores. "They’ll beat the system, no matter what," he said.

The bill has an effective date of January.