Cow Diseases

[karlrolke]

I want to get opinions on a fictional disease scenario:

The story:
Early summer- Morning, found 2 older brood cows nursing young calves -- dead

Information:
Pasture has cool season grasses/few legumes/heavily fertilized (on a barn site years previous was burned)
The 2 dead were previously found grazing at this site
Other cows experiencing nervousness

Any Idea what disease this could be and why?

 

[wbvs58]

Lead, nervous signs and old barn site would probably have contained lead in some form.
Ken