Hi. We had a cow diagnosed with grass tetany and she died as a result. Is there any way to prevent it? How does the disease process actually work? I had noticed her quieter for about 1 week but she was due to calve any time and some cows will be like that. She went down hill immediately after calving and died 2 days later. Are there particular grasses associated with this condition?  

Answer:

Grass tetany or "hypomagnesemia" is a condition caused by low blood magnesium.  It can occur in all classes of cattle including pregnant cows but we most commonly see it in cows that have recently calved.

It is usually seen in cattle grazing a lush pasture dominated by grass or green cereal crops.  These types of feed are predisposed to low magnesium and this predisposition can be worsened by the application of manure that is relatively high in potassium.  The potassium competes with the magnesium in being taken up by the pasture and causes a feed that is too low in magnesium.

 To prevent it feed a good quality mineral to your herd year round.  If you are not currently feeding mineral feed it for a month and then get blood work done to see if the levels are adequate and then the feeding rate of mineral can be adjusted if needed.

~ Dr. Mac Littlejohn