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In what's thought to be one of the biggest dog rescue efforts in the U.S., nearly 4,000 beagles are looking for forever homes after being saved from a Virginia facility that bred them to be sold to laboratories for drug experiments.

Animal rescue organization volunteers started moving the first batch of dogs late last month, the U.S. Humane Sociality reported. As of Tuesday, just over half of them had been removed, the non-profit reported on its website.

"I was able to bring out the very first puppy and it gets you. To know what these dogs were destined for and where they are going now, it's indescribable," said Kitty Block, president and chief executive of the U.S. Humane Society.

Shelters from Illinois to Pennsylvania have begun receiving the dogs to give them medical exams, vaccinations and other treatments before they are ready for adoption.

"It's going to take 60 days to get all of these animals out, and working with our shelter and rescue partners across the country, working with them to get these dogs eventually into ever-loving homes," Block told Reuters.

The plan to remove the dogs kicked off when the filed a in May against Envigo RMS, which owns and operates the Cumberland, Virginia, facility that breeds beagles for medical research.

According to court papers, the U.S. Department of Justice alleged Animal Welfare Act violations at the facility.

"It's very unprecedented," said Audra Houghton, the Humane Society's Animal Rescue Team director. "I don't think there is anyone on our team that has seen 4,000 dogs in one location at one time in their entire career."

Federal officials accused Envigo of a chain of animal welfare violations at the facility—including dogs receiving insufficient food, inadequate medical care, housing in filthy conditions and some being euthanized without anesthesia. An inspection report from the U.S. Department of Agriculture found that, between January and July of last year, more than 300 puppy deaths were attributed to "unknown causes"—with the facility not taking any additional steps to investigate the deaths or prevent similar losses in the future.

In June, parent company Inotiv Inc. said it would close the facility. In July, Envigo settled with the government, without paying any fines.

"The Cumberland Facility was recognized as needing improvements and investments," Inotiv's Chief Executive Officer Robert Leasure, Jr. said in a statement released to U.S. TODAY Wednesday. "Our work and the work of our clients is essential to saving . Without critical drug discovery and development efforts, millions of people around the world would continue their lives devoid of any hope for treatments and cures to life-threatening diseases. Our top priority continues to be ensuring proper animal welfare and regulatory compliant practices at all of our facilities."

The Humane Society does not adopt animals directly to the public.

On its website, the non-profit wrote its shelter and rescue partners plan to place the dogs into foster and adoptive homes.

"While these dogs prepare for the next stage of their new lives, our work is far from over," the non-profit posted on its Facebook page. "Please, rush a donation to help transfer the remainder of these dogs and give more animals a better life."

More information: For more information visit www.humanesociety.org/beaglerescue, where names of shelter and rescue partners aiding with placement are listed as they are confirmed.