We had mucho problemo with pinkeye in our heifer calves this past fall and winter. We boostered our IBR vaccine and gave pinkeye shield at Thanksgiving because of all the problems, didnt seem to help. I agree with Kato that feeding round bales contributed to the problem. In January I started unrolling the bales in a small pasture, rather than feeding them in bale feeders, and saw a big difference. Here's what I learned about pinkeye - it becomes a problem when the bacteria is present and the eye is scratched, whether it be dried up clover in the pasture, stems in a bale feeder, ect. From what I read, there are two bacterial forms (M. bovis, M. ovis) and also the viral form, but the ovis form is found in the eyes of healthy cattle too. BEEF magazine had an article about it, I think you can look at it online. Anyhow I found that protecting the eye is every bit as important (if not more important) than administering a vaccine. That being said, we've fed round bales in feeders for years with very few problems. I think if we have the problem again, we'll either grind hay or winter them in a bigger pasture where we can unroll the bales better.
I agree with BMR that perhaps the IBR mutates. We vaccinate against it in the spring and before weaning, plus the extra dose in November last year, so they should have been good.
We cultures some samples in December and found both M. ovis and M. bovis in the calves with bad eyes. The vet said that usually the bacterial forms aren't a problem in the winter.
Our vet has been practicing for close to 40 years and our pinkeye issues this past fall/winter left him scratching his head.
