Grass Staggers (hypomagnesaemia) or
"lactation tetany" is an acute disorder
characterised by sudden death and caused
by low levels of magnesium in the blood.

Factors include:
1) young, rapidly growing spring grass
can be low in magnesium
2) individual ewes vary in their ability to
absorb magnesium
3) nitrate fertilizers increase the protein
in the grass which in turn produces
excessive amounts of free ammonia in the
rumen, lowers rumen pH and depletes
carbohydrate. The imbalance of
carbohydrate to nitrogen may depress
appetite, making matters worse.
4) lush spring grasses pass thru the
intestines very quickly, which allows less
time for the magnesium to be absorbed
5) magnesium may be less available in
acid soils
6) the level of sodium in fertilized fields
is low, which means that the ratio of
sodium to potassium in the rumen is
upset.

Clinical signs:
Clinical signs usually last for only a short
time, therefore the shepherd may only
find a dead ewe.
1) stiff, stilted walk - often with the head
held high
2) nervous twitching of the face muscles
and frequent urination
3) exaggerated alarm to noise or to the
sucking of the lambs
4) being gathered and caught is
particularly stressful and may precipitate
convulsions and death, so ewes must be
approached with care
5) sheep will develop a "wild-eyed" look
and appear to be blind, grind their teeth
and eventually go down. They usually lie
on their side with the legs stretched out
straight, their head thrown back and the
neck rigid.

For more information on this, please
consult Dr. David Henderson's book
"The Veterinary Book for Sheep
Farmers" from which this is excerpted.