MERCER, Pa. — Joe has trained 21 dogs during his stay at the State Correctional Institution at Mercer. This week, he is saying goodbye to the latest one, Tonka, a wiggly white Lab-terrier mix with a pink nose.

Every eight weeks, six dogs enter the minimum-security prison and are assigned to two inmates who are trained to prepare them for successful adoption.

In a five-year relationship with Strayhaven Animal Shelter in Greenville, Pa., in Mercer County, SCI-Mercer has taken 122 dogs, and all but one have been adopted. Many come in with behavioral issues, but their better personalities emerge during the training.

Corrections staff members say the same thing about the men — whose last names and crimes are not included in this story in an agreement with prison officials.

"This is definitely a reward for someone who’s locked up," said Gregory, whose current dog is Ooglie, a 5-year-old shepherd mix. "She was taken to Strayhaven by her family, so she was rejected. A lot of dogs come from broken homes, a lot are abandoned. It’s good to see their personalities come out" when they have a buddy. "Some days, it doesn’t feel like I’m locked up when I’m working with a dog."

Many prisons, in Pennsylvania and nationwide, pair shelter dogs with inmates. The programs are called by different names and train dogs for different skills, including service to people with special needs, said Lisa Graves, the director of the program at Mercer. Mercer’s program with Strayhaven is called Canine Adoptive Rescue Endeavor, or CARE.

The Mercer partnership relieves the animal shelter of overcrowding and improves its flow of adoptions, said Jennifer McCurdy, manager at Strayhaven. The training the inmates provide is a star on the status of a dog that has been hard to place, she said.

Before their adoptions, the dogs at Mercer are tested for basic discipline like sitting, staying, disposition on leash and anxiety when the owner leaves.

During a recent test, training instructor Katie Costello approached Midna, a sleek black hound mix with a brown mask, and Ron, her primary handler. She patted Midna, shook hands with Ron and ran a comb over Midna’s back. She summoned Graves and Randy Rickert, a staff counselor, to walk toward them, like extras in a crowd scene, to test Midna’s self-possession.

"Have her stay and walk away," Costello said, and Ron said "Stay!" and walked away. He hid behind a desk. Time passed and the dog looked at Costello. She looked around the room. She put the dog’s front paws on a chair to look out the window. No Ron there. Then the dog sniffed the clipboard and sat down. When Ron emerged from behind the desk, Midna’s tail flipped like the rotor of a helicopter.

Special tricks are the fun accomplishments of having time to do it. Joe gets Tonka to roll over using hand signals and treats. Midna can do an air pirouette, which she demonstrated one day in a fenced play area outside. Juan, Midna’s other handler, and Aaron, who co-trained a shepherd-mix named Sky, were playing keep away with the two dogs. As the dogs ran toward Juan, he called out "three sixty!" and Midna leaped and twirled.

"I’m so incredibly impressed with what these guys do," said Costello. "As we get close to graduation day, you can see their sense of worth. It’s definitely a mutual benefit."

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Ron was days from his release when Midna took her test. Playing with her beforehand, he placed a liver treat on his knee, his hand in the air, as Midna sat very still, inches away. When he gave the signal, she grabbed the treat and Ron kissed the top of her head.

"This is my third dog and she’s been my favorite," he said. "She sleeps with me in my bunk."

He said he would love to adopt her but can’t because he is moving into a halfway house.

In his and Juan’s cell, the hound spends part of her day in a crate at the foot of the bunk beds. The men have tacked photos of all the dogs they have trained on a bulletin board on the wall.

Star, a 7-year-old shepherd mix, came to the prison needing behavioral correction and has since stopped getting into the garbage and begging, said Paul, her primary handler.

"I like older dogs for the challenge," he said. "I’m here to serve my time, but this gives me another purpose. It also helps with my (post-traumatic stress disorder), so I’m very grateful.

"I’ve taken her to PTSD sessions and she makes the other guys more relaxed, right baby?" he said, caressing Star’s neck and rubbing her head with his forehead.

"This program should be at every jail," said Joe, whose pink-nosed Tonka nuzzled his leg. "It gives the guys a sense of pride, it makes us better people and we’re helping these animals."

But there’s always the hard part — saying goodbye to a friend who has lived with you, is always crazy to see you and who looks you in the eye the way dogs always do and humans often don’t.

"I fall in love with every single one of them," Joe said. "That’s the blessing in reverse."

Strayhaven’s Facebook page shares stories about its CARE program with Mercer.