Interesting theories among the comments. Apparently there is a veterinary theory that it was simple heatstroke. Objection is that it was all the cows on one farm and not neighboring farms. Someone calculated the insurance claim possible... == millions. It would be possible, I think, to induce heatstroke in ways that would not be traceable like poison. My objection is doing it so that all 10,000 would die at once. Then there's the black helicopter sighting which has no refutation as a fallback.