Cows with low magnesium run the risk of loss of production, going down at calving with “grass staggers” and death, at a time when you can least afford these losses.  

The problem is that it's difficult to boost the cow's magnesium levels quickly and you have to charge up its battery over a long period.  Cows that have grazed tightly when feed was short are at greatest risk, as their intake of magnesium will have been greatly reduced.  Once the herd's blood magnesium is low, even with supplementation it is hard to get levels back to normal. 

Farmers should consult their veterinarians and have the herd's blood magnesium levels checked.  This can be done from a blood sample and is very quickly completed after the samples arrive at the lab.    

Have a quick check of the magnesium levels done on a sample of the cows.  About 10% of the herd is sufficient, but leave out the heifers.  Then you'll be able to decide if emergency action is needed. 

A test can pick up a range of potential problems and although it may tell you bad news, at least you have a chance to work out what to do about it before it is too late.