That applies to all apples, not just crab apples. It applies to humans and other mammals as well. Deer are able to eat piles of them very often will no ill effects. Now, a deer is obviously not a dog but the amount of seeds you would need to consume (and crush before consumption) for levels to be lethal are insane. I've researched this before giving my dog normal apples. She gets the occasional whole apple and eats it, core and all. That's not to say crab apples could theoretically have higher concentrations but from the little bit of research I've just done, I don't see why there would be an issue if a dog were to consume just the flesh of crab apples with the core and seeds removed. I'm going to look into this more and will still consult my veterinarian before allowing it. I'm mostly curious because make batches of food topper with brown rice, chicken gizzards with hearts & livers, carrots, green beans and wild Maine blueberries. I also make her biscuits at home with rice flour, pumpkin, eggs, natural peanut butter and a dash of cinnamon. I'm curious if I could safely incorporate the apples into her diet, as they grow everywhere in the State of Maine.

P.S. thank you for mentioning that cores amd seeds of apples have the potential to become problematic if consumed in high enough quantities. Not a lot of people are aware of that.