Well from what I remember without going and digging out my notebook
:
Caused by magnesium deficiency.
Symptoms are the cow literally staggering about, discoordination, head thrown back etc. Can lead to death in extreme cases (I think)
Treated by giving the animal magnesium (I think subcutaneously but I could be wrong??). Can be prevented by providing mineral licks or by using 'magnesium bullets' or boluses that last a few weeks when swallowed.
EDIT: AC got there first with a better answer, ignore me!