The simplest way would be to collect some fresh droppings from one or more chickens, and take them in to your local vet for a fecal float. Confining one on a clean towel or puppy pad overnight in a dog crate would be good. I would call around and check cost and if they can give you a report the same day or how long it takes if they send it off. Your regular vet might be more inclined to perform this if they don't normally do chickens. Or you can just worm them all with Valbazen or fenbendazole (SafeGuard liquid goat wormer or horse paste.) Instructions are in post 5.
