January 17, 2015 12:10 AM

These days Brooke Burton has a hard time keeping up with Dennis, her 6-year old Dachshund, who loves taking walks and chasing tennis balls. It’s hard to believe that this rambunctious 13-lb. pooch is the same obese pet she discovered in 2013 at the home of an elderly relative.

“My great-uncle was a hoarder, and I went over there to help clean his house,” Burton tells PEOPLE. “Then I saw this thing coming toward me like a slug. He would take a few steps and then have to rest.”

Burton, 27, took Dennis – who weighed 56 lbs. thanks to a diet of fast food burgers, pizza and frozen dinners – back to her Columbus, Ohio, home, effectively saving his life.

“The vet said he would not have made it another month there,” says Burton, adding that Dennis was severely dehydrated and suffering from ear and skin infections.

She immediately put Dennis on a restricted diet (½ of a cup of dry dog food, twice a day) and eased him into regular walks. Once the weight dropped off, with the help of donations from crowdsourcing, Burton was able to get the pup a much-needed skin removal surgery.

“His whole personality has changed,” Burton tells PEOPLE. “He is always looking for someone to play with. And he loves to bark orders.”

For more on how he lost the weight and Dennis’ life now, pick up the latest issue of PEOPLE on newsstands now

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