"We just had lots of pets from the moment I was born," the actress tells PEOPLE. "I grew up with a black lab named Ben. There are photos of me laying and teething on his ears."
The love affair continued as Heigl grew up, and ultimately led to the creation of the Jason Debus Heigl Foundation, an organization named in honor of her late brother that helps low-income families get their pets spayed or neutered and funds the transport of dogs to no-kill shelters.
"We have to diminish the number of animals entering shelters," the actress, 35, says. "There are enough homes but there aren't enough people adopting. They're buying, so animals end up in shelters and because there's not enough space, they have to euthanize or kill [them]."
At home, Heigl certainly practices what she preaches, having adopted eight dogs with husband Josh Kelley. Each one of them has a special role in Heigl's life; for instance, "Piper, a shepherd-lab-chow mix. She's just really sensitive to me," Heigl says. "If I'm upset or crying she will find me, even if she's all the way on the other side of the house. She just senses it."
Her young daughters are learning to love dogs, too. Heigl's 5-year-old, Naleigh, and her 2-year-old, Adalaide, can't get enough of the pooches, the actress shares.
"Naleigh is really into them, but Adalaide is obsessed," says Heigl. "When she was 6 months I was trying to do tummy time and she hated tummy time. So I put her on her tummy and [dog] Oscar was there and he started licking her face. He loves the kids."
However the entire family – furry and not – likes to cuddle on the couch each night. "Josh and I have a ritual after work," says Heigl. "After the kids go to bed we pour a drink, hit the media room and all pile up on the couch and watch movies together."
Compared to her husband's feelings, Heigl's love for dogs is on another level – but she wouldn't have it any other way. "If you're talking from one to 10, I'm like a 40 and Josh is probably like an eight," jokes the actress. "I'm insane and he's normal. He has his favorites but he's become very attached to Gertrude," whom he finds quite entertaining. "[A dog] that makes you laugh like that every time you look at them, that's a real blessing."
For more from Heigl, pick up the June 30 issue of PEOPLE, on newsstands now