Fran, dogs don't really digest whole veggies. One thing I learned many moons ago on barf lists, if you want your dog to fill up, serve in chunks. You want your dog to get any benefit … smash them up. If you want to check it for yourself, give your dog several chunks of different veggies, check the poo. Often what you find looks pretty much what goes in.
That said, mine love apples. USUALLY they chew them up. I got up to Cara throwing up 2 days ago-- on big apple chunk and liquid. Sigh. Guess I'll slice much smaller.