I am beginning to think that the Bulls(brought in) are the main culprits of pinkeye. This year i used my own bulls that i raised, picked out the best bulls from the best cows......usually by now I have a half a dozen or so severe cases of pinkeye.....so far not one case. maybe its just a fluke...we'll see.We have a few cases a year, and like some have mentioned some years a lot more than others. I think in those times it is likely a new strain. Last year was pretty rough, had it in cows and calves. So far this year, just a bull and a few calves. When ever we notice a watery eye or the slightest hint of something we are treating it. Some years it would only be in a newly purchased bull and would then apparently spread to a few calves.