The pups, who were being used for toxicology tests at labs across five states, were saved by the Beagle Freedom Project.
A moving video shows the moment 38 beagles felt freedom for the first time after spending their lives in cages.
The pups, who were being used for toxicology testing at labs across five states, were saved by the Beagle Freedom Project after a veterinary technician contacted them to say the animals were going to be euthanized at the end of the experiment.
After the dogs were rescued, they joined new families across 11 states in the biggest ever effort of its kind.
In the tear-jerking video, staff and volunteers can be seen collecting the animals from labs before releasing them for the first time.
Speaking to INSIDE EDITION, the Beagle Freedom Project's Director of Operations Kevin Chase said the beagles reacted differently to their new-found freedom.
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"The boys were all quite happy to be freed," he said. "They were running around and jumping with each other. But the girls were very, very passive and shy and fearful - especially of men."
He said that after being freed, the dogs are often nervous and show signs of PTSD - but that they get better over time with the love of their new owners.
"They are wonderful," he said. "They make for great family companions."
He added: "They live through their noses... In their cages, all they smelled was ammonia, urine and blood. Now they love to be outside with their noses stuck to the ground, and love taking long naps in the sunshine."
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Chase added that 383 labs in the U.S. use dogs in testing. In total, there are around 65,000 dogs being used, according to the USDA, and 95 percent of those are beagles.
The breed is used due to their gentle natures, Chase said.
The Beagle Freedom Project is fighting for every state to agree that labs should contact local shelters when they are about to euthanize beagles.
For more information on the group, visit its website.
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