Hook was correct in that based on facts my answer was short... however any cattle under 1 year old sudden death.. blackleg is the first thing to consider. As Hook pointed out, easy if vaccinated, if not still might be BL. I understand you can rub legs of carcass and it will crack or pop like wadding up paper. Other possibilities? Lightning, Perilla Mint, Cherry leaves, other poisons either uncovered for some reason in pasture or just deposited in pasture. Always made me real nervous when I lost a calf and didn't know why. Feared the others were as risk, until I was certain.
One other question... and I don't wish to steal this thread, but...
if unexplained death without wounds, how do ya'll dispose of carcass? Bury. Burn. Predators (coyotes, dogs domestic or wild, buzzard etc? If a diease it really makes a difference.