The leader of the nation's largest animal breeding registry joined animal welfare groups Tuesday in urging Congress to expand federal regulation of so-called "puppy mills."

The American Kennel Club, which has opposed changes to the Animal Welfare Act in the past, decided "the time has come to bring under regulation high-volume breeders and brokers who sell at retail or who import puppies in volume for resale," said chairman Ronald Menaker, whose group registers nearly 1 million purebred dogs a year.

Menaker testified at a Senate agriculture subcommittee hearing on a bill that would add oversight to these operations in an attempt to curtail cruel conditions for adult breeding dogs and their puppies, which are sometimes sold for thousands of dollars.

Some small breeders and pet store operators oppose the regulation as unnecessary.

Sen. Rick Santorum, R-Pa., a sponsor of the Senate bill along with Sen. Richard Durbin, D-Ill., noted that groups that, in the past, have had a prickly relationship were working together on the bill.

The bill would extend regulations to those who sell more than 25 dogs per year, and it exempts those who raise up to seven litters a year on their own premises.

The Animal Welfare Act, which mandates a basic standard of care for animals, currently exempts retail pet stores from federal oversight. Large breeding operations are considered retailers by the Agriculture Department if they sell directly to consumers.

In the 30 years since the act was passed, the Internet has opened up a new market to these retailers, helping them to sell puppies around the country.

Michael Maddox, legislative director of the Pet Industry Joint Advisory Council, a pet trade industry group, testified that pet stores were exempted because they are subject to broad public exposure and are frequently regulated locally.

Maddox said that one provision in the bill mandating oversight of those who sell 25 animals a year imported from other countries -- even at pet stores -- goes beyond the intention of the original law. He said the bill would overburden inspectors and wasn't necessary.

Menaker praised a provision in the bill that exempts the operations that pass inspection standards set by not-for-profit organizations certified by the Agriculture Department.

Wayne Pacelle, president of the Humane Society, testified that just last week 151 dogs were found in the home of a retail dealer in Vero Beach, Fla., in a condition he described as "skin and bones."

Leaders from the American Veterinary Medical Association and the Doris Day Animal League also testified on the bill's behalf.

"This is a problem here and now," Pacelle said.