I personally go the herbal route. I use Fir Meadow's GI Soother and DWorm A. For prevention you give at least 3 times a week, and every day after it rains. For treatment I give it every 15 minutes for an hour, then hourly til runs are gone. From then out I give it every 3-4 hours till pellets are completely solid, then 3 times a day after they've recovered. I am extremely happy with it. It cleared up two cases for me this year, faster than the chemicals I used last year. With one case, he made an almost complete turn around in a single day. It's a great option if you want to support the natural flora in their gut, and reduce resistance in your herd.
If I was to go chemical, DiMethox has been successful around here. I used Sulmet last year, but I think there is more resistance to that now. If you dilute Corid (and I would suggest coupling with B Complex) that should be a fine option too.
