Detectives, deputies and about 50 specially trained volunteers seized more than 400 dogs from what Humane Society officials called one of the nation's largest and worst puppy mills.

"The conditions were not only shocking, but also heartbreaking to veteran deputies," said Benton County Sheriff Larry Taylor, who led the effort to confiscate the dogs Wednesday from the home of Ella Stewart.

Part of the street in front of the home just outside of Kennewick was blocked off as volunteers loaded dogs into a 75-foot semi-truck with cages built into its air-conditioned trailer. The rig was used to carry the dogs to the Benton County Fairgrounds where temporary kennels had been set up. The animals, including three newborn puppies, will be moved before the annual fair starts in August.

Dogs were found living in wooden crates, shopping carts and other makeshift kennels caked with feces and soaked with urine, investigators said. Detectives wore gloves and put booties on their shoes before walking onto the 2-acre property to serve a warrant to seize the dogs, assess living conditions and collect any documentation of animal sales.

All the dogs will need some medical care and some will need extensive treatment, Taylor said. Some dogs suffered from malnutrition while others had urine burns and overgrown nails.

Stewart, 66, breeds miniature American Eskimo dogs at her Sun Valley Kennel. She was home when the sheriff's deputies arrived and Taylor said she was cooperative.

Stewart was arrested May 12 after a deputy found what investigators described as deplorable conditions at her kennel while responding to an unrelated call at a neighbor's home. She pleaded innocent to one count of second-degree animal cruelty in Benton County District Court and will be back in court in early June.

The misdemeanor charge carries a maximum penalty of 90 days in jails and up to a $1,000 fine. But prosecutors reviewing the case said they may file additional charges.

A telephone call made to Stewart's residence Thursday by The Associated Press was not immediately returned.

"This is definitely one of the worst cases we have seen because of the conditions they were kept in," said Inga Gibson, state director with The Humane Society of the United States' West Coast regional office. "It's one of the largest in Washington state and close to one of the largest in the country."

The dogs weren't seized two weeks ago because the county doesn't have an animal control facility and had nowhere to house them. It also took time to find a licensed veterinarian to check out the dogs and animal rescue groups to help, Taylor said.

Animal control doesn't fall under the sheriff's jurisdiction, but Taylor said he was glad to take the lead.

"My position is we're in dire conditions. I'll worry about the finances later," Taylor told the Tri-City Herald. "This isn't something we run into every day. This has a tremendous impact on the sheriff's office and the county."

Food and other supplies have been donated by Pet-Smart Charities.

In addition to The Humane Society, rescue groups that are helping include Emergency Animal Rescue Services from Seattle; United Animal Nations from Sacramento, Calif.; Humane Evacuation Animal Response Team from Spokane; and Spokanimal CARE from Spokane.

Taylor said they still need more veterinarian assistance.

A couple of neighbors thanked a group of deputies as they walked by.

"I'm greatly relieved. Words can't describe the joy and relief," said Helen Richardson, whose daughter has lived next door to Stewart for 20 years.

Richardson said the family has been saddened by what they've witnessed over the years and frustrated that nothing was done sooner.

"The lack of smell will be fabulous. Just knowing this has come to an end is fabulous," she said.