------- Original Message -------
>From : leon[mailto:leon@grazinginfo.com]
-Animals are often found dead. Thrashing indicates grass tetany while none
could indicate milk-fever. The cause can be confirmed by collecting a urine
sample from the urinary bladder where the Mg level will be low. The Mg level
in the blood of down animals or about to go down with GT is low. Once down,
the blood Mg level can increase as Mg is drawn from the rest of the body,
especially from the muscles that are no longer being used, so to be
meaningful the blood should be measured before the animal goes down.
So the statement, ��If the cow is down, draw a blood sample before treatment
is given,�� needs correcting.
Here in the US, hypomagnesemia is most commonly encountered in post-partum beef cattle - typically in winter/early spring with a 1-2 month old calf nursing, or in stocker cattle grazing wheat pastures. I've never yet seen a case of pure hypomagnesemia in a dairy cow, but have never attended any dairies that were strictly grass-based with no feeding of grain ration, corn silage or harvested forages.
I never bothered to collect a blood sample and have it analyzed prior to initiating treatment - most of those cows can't wait the two days it would have taken to get those results back from the diagnostic laboratory.
In my own practice experience, if the cow was already down and convulsing/seizuring, I was NEVER able to 'save' them. Every one I ever saw in that condition died, in spite of administration of the recommended treatments.
If I could get to them while they were still ambulatory, albeit shaky, or even down, but still able to sit up, they usually responded well, and achieved full recovery.
Beef producers here frequently feed 'Hi-Mag' blocks, but typically, these blocks do not contain sufficient MgO for the animals to ingest sufficient amounts to prevent GT; I prefer a free-choice loose high-Mg mineral mix. In some herds, I've had to get them to switch to a 50/50 mix of trace mineralized salt and MgO in order to get enough Mg into the cows - MgO is very unpalatable, but at least with this combo, when they do ingest the mix, they get a good slug of Mg.
We routinely confirm the veterinary practitioner or producer's suspicion of cow death due to hypomagnesemic tetany by analyzing Mg levels in blood or vitreous humor from the eyeball.
Louis L. Pittman, Jr., DVM
Veterinary Pathologist
Murray St.Univ. - Breathitt Veterinary Center
Hopkinsville KY
