Kaley Cuoco, best known for her role as Penny on The Big Bang Theory, hates people who lack loyalty to their pets. An ardent defender of animal rights, the actress has adopted several dogs. Ten years ago, Cuoco began rescuing abandoned animals, starting with pit bulls, after she learned that the breed was mistreated due to its reputation.

"I was like, 'Oh, my God. I'm obsessed with this kind of dog,'" she said. "I just found them to be so incredible. I realized what great dogs they were, and how horribly they were seen. And I just didn't want that to happen anymore. So it became a passion."

Soon after, Cuoco, 33, adopted her first rescue – a two-year-old pit bull mix with a broken leg who she named Norman. "I knew right away," Cuoco said. "I wanted this dog to be in my life."

Norman is a hit on Cuoco's Instagram, which has 3.2 million followers. Other fan favorites include Shirley, another pit bull mix and Norman's sidekick, and Ruby, a shaggy terrier mix, as well as seven professional show horses. Cuoco works with Paw Works, a nonprofit rescue organization that works with shelters across Los Angeles to find foster and adoptive homes for abandoned animals.

According to the Humane Society, pet overpopulation has become a national crisis. The organization says that every 13 seconds, a healthy, adoptable dog or cat is euthanized in a US shelter. Almost 3 million pets are put down in shelters every year, and about 80 percent of them are healthy and could have been adopted into new homes. Paw Works has expanded the “no kill” county model throughout California, working to promote pet ownership through education and programs that offer free spaying and neutering, training and veterinary care in underserved and low-income areas.

Currently, Cuoco fosters several abandoned animals that are searching for a permanent home. "You know, an animal is so innocent," she said. "They have no voice. ... I want to kind of be a voice for them and speak up for them."

The actress hopes to shine a light on animals who are abandoned at L.A.'s overpopulated and underfunded shelters. "It's because they're old," she said. "So many people come in and drop off dogs they've had for years that they don't want anymore because they're old."

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Cuoco says that many owners say that they abandon older animals due to the cost of care. For the actress, however, that’s not an excuse. Owners should think of their pets as family and afford them the same care they would any other relative. "I live by this saying," she said, "I don't know who quoted it, but it's like: Who rescued who?" she said. "And I just think it's the sweetest thing. Because it's true. It changes your life."

This Valentine’s Day, Cuoco’s husband, Karl Cook, gave her a new rescue puppy, which she named Blueberry.