sorry to hear about all the tragic ways of livestock dying, but years ago when i was first starting 4H we got some calves out west brought em' home, worked with em' the next few weeks and one day working em' in the pasture we had one that was so strong and me only being 10 or 12 at the time little girl. we tied to the back of the tractor lightly pull him around as we walk next to him, and he was mostly broke stubborn at times but we really didn't DRAG him... anyway without no warning, no heavy breathing, just started bleeding from his nose and fell over and died.. Surprised I'll say and mind you he was only working with us for not even ten minutes that day. we just took one 30 foot walk and he collapsed and was dead instantly...
heart attack? who knows....