The fescue issue you are refering to is usually caused by ergovaline (an alkaloid) formed by ergot (a fungus). Ergovaline is a vasal constricter and cows don't build a resistance to it, but have no problems with low dosages of it. We often feed fescue straw (fescue hay that was cut and baled after the fescue seed was combined off) at 50% of the ration. We feed it to hundreds of cows each winter as a low cost roughage source (we grow fescue seed too). We have a lab test done first to see what the ergovaline level is (some fescue varieties are ergot free). Once we know we can then determine how much of it can go into the ration safetly. Accidentally feeding excessive amounts of ergot in the summer months is usually not critical. You will find the cows standing in water (because of the fever), drinking excessive water, and going off feed for a day or two. They pass the feed and their metabolism returns to normal. In the winter though the ergovaline restricts blood flow to the extremities causing frostbite and the lose of tails, ears, feet, etc. Often you loose the cow. We had a case a few years ago, in the neighboring county, of a guy loosing two hundred head because he bought fescue straw cheap and that was all he fed to his cows in the winter. FYI you can find ergot in bluegrass hay/straw as well. A neighbor of ours cleans fescue and bluegrass seed in their plant. They pelletize the screenings and feed it in their feedlot. The ergovaline levels are often extraordinary. They remedy this by feeding MTB by AllTech. It apparently binds the alkaloids. They used to have to dump hundreds of tons of screenings, but now feed it out. We havn't tried it yet, but it is on the list of things to try.