I'm a lab owner and love them!! As for fiber, I have added cooked oats to their diet. Beet pulp is said to be very good, but I have not tried that. I know you said your pup doesn't like pumpkin, perhaps mixed in with the oats, would work. One recipe I've cooked over the years, is...either ground Turkey, beef, or chicken (depends on your dog, as for meat choices) browned in organic coconut oil, and/or olive oil, then add either oats, or brown rice, green beans, unsalted chicken stock,..when that's all cooked, then add tumerick and black pepper, and cook only for a few more minutes. The tumerick and black pepper are a healthy addition, not necessary. Black pepper works as a boost to turmeric. All said...maybe a couple tablespoons added to your labs food would help. I make a big batch, and freeze portions. Hope this helpful!!