We feed our cows well, have them on a mineral program and give scourguard as well. I think it comes out of the ground depending on the year and the conditions. Seems like a wet, warm year is worse than a cold, snowy one. I had a year or two that were nightmares. Since we started vaccinating, things are much better.  Funny how we all have different stories and it works differently in different areas. My way works here and thats what counts. Sure can always learn new things though.