I read this somewhere recently and thought it was a helpful hint to pass on to my Bloggies. Garlic is a natural remedy for intestinal worms in chickens as well.  Just crush a clove and place in a piece of cloth or stocking and steep it in the chickens water for a few days.  Do this about four times a year to keep your girls happy.
Growing parasite repellent plants in and around your coop will also benefit your chickens. Lavender, Rosemary and Geraniums are perfect and small sprigs of these can be placed in the nesting boxes. Keep them happy so they can keep you happy.

Cluck Cluck Cluck