We have problems with Black Leg in one of our pastures. It is spring fed and in Coastal Bermuda (not Tifton). During wet season we get outbreaks unless he cattle are vaccinated for it. Must be 6 months old to vaccinate, but nursing calves are protected by mother's milk.
Had one nearby farmer loose almost an entire calf crop to it.
If a heifer or calf is infected, it dies. Nothing will stop it once infected. Only vaccination works.
Another possible is prussic acid. Drought stress can cause it in Coastal Bermuda.
It didn’t say but it sounded like most of his herd. They died almost immediately.