I've read that pumpkin seed is also a natural dewormer..maybe just a preventative? My birds don't seem to like the seeds but the love the pumpkin itself so much that last year I had a bunch of hollowed out pumpkins in the garden with chicken butts sticking out where they ate them and then crawled inside to keep eating.
Your chickens would have to eat a pickup truck load of crushed pumpkin seeds in order for it to be effective. A 125ml bottle of Safeguard liquid goat wormer is cheaper, quicker, more effective, and very safe to use.