Seems like one a year - perfectly healthy animal on grass hay all bloated up and dead in the morning. My ground in very uneven and this time of year the clay gets super greasy especially when it's hard frozen underneath and starts to melt on top. Seems like if they just get laying the wrong way a little bit, they can't get up sometimes. Caught two yearling bulls last year before it happened and managed to get their feet rolled underneath them before they died. Of course, if you don't see it happening, you just do really wonder. This last one happened last night. Young seemingly healthy cow laying down where they always lay out of the wind - all bloated and dead. However head was pointing down slope. Always a sign - but never a certainty. I also once read to move hay feeders around this time of year. Lost a yearling heifer to cast (I think) one year upside down in a tractor tire run next to the feeder.