I recommend valbazen (albendazole.) It is a cattle and sheep wormer. Your feed store might carry it, if not you can order it online or call jeffers livestock.com at their website. It's a liquid and dosage is 1/2cc for standard chickens, 1/4cc for smaller chickens. You have to give it to each chicken orally. It is the best wormer on the market and kills many kinds of worms over 2-5 day period. Egg withdrawal is 14 days. The bottle it comes in will last you a long time.