As usual, I think Dun hit it right on point on the hay testing. If I didn't personally see the hay field growing and being cut I'd always have it tested for nitrates & prussic acid, ESPECIALLY if it is Sudan, Haygrazer or Johnsongrass hay. Find a good hay man and consider sticking with him. Ask direct questions of your hay supplier regarding the growing conditions, whether or not he had the hay tested, etc. Having done that, and if he lies to you, you may have some legal recourse (although, generally speaking, I hate the litigous nature of our society). I know of several cases of hay men have been successfully sued for selling "horse quality" hay to horse owners where the hay was far from "horse quality". Also, a lot of unscrupulous (or simply unknowing) guys will bale really drought stressed hay and sell it without testing it. I've never felt the need to test Bermuda or Bahia for nitrates, but of course protein testing would still be good do do. It's always a good idea to know how much nutritional value your hay has so you know if certain supplementation is warranted. The tests can be done quite inexpensively at your local ag school, county extension office, etc.