Grass tetany comes on quickly, is often fatal

Several herds in our area have been affected over the last few years with grass tetany, an often-fatal syndrome caused by a magnesium deficiency. 


These herds will often have multiple cases in short order. 


Chances of recovery are poor once affected cattle start going down, so treatment is an emergency.


Treatment can be successful if the disease is caught early, and a veterinarian will initiate steps to prevent further cases. 


Mineral feeding has been sporadic to non-existent for the past year in almost all the cases I have seen. These deficiencies may be a long time coming. 


Factors that can contribute to the disorder include stresses such as weather changes, starvation for even 24 hours, heavy pregnancy and milk loss from sucking calves. 


Mature, lactating cows are usually affected first.


Changes to lush green pastures coupled with inclement weather can also precipitate an outbreak. 


Lush grass lowers magnesium levels.


I have seen an outbreak occur after the weather turned inclement in a group of well-doing heifers on a sound mineral program that were starved for 24 hours to facilitate spaying.


It is not uncommon for more cases to develop rapidly if one cow is magnesium deficient. One must assume the whole herd could be borderline deficient. 


Cattle in a classic case of grass tetany become weak, start to stagger and go down, developing tetanic convulsive fits.


Paddling with the front feet and snapping of the eyelids can also occur, along with heavy breathing and foaming at the mouth. 


Veterinarians examining affected cattle often find a high heart rate and potentially elevated temperature from the hard work the muscles are doing.


Veterinarians often administer a combination of calcium, phosphorus and magnesium, much as they would treat milk fever. 


Deficiency in these three minerals may be enough to cause a downer cow.


Most clinics can do blood work in house, so many veterinarians will often take a blood sample before they begin to check for the levels of these minerals. 


We often see magnesium and calcium low together.


Occasionally we look for high potassium, another macro mineral, because it can interfere with magnesium absorption from the rumen and lead to a secondary grass tetany. 


The real problem with grass tetany is it usually comes on quickly without warning, and death can be sudden.


Post mortems show little, and veterinarians are often left scratching their heads unless clinical signs are seen. 


Combination calcium, phosphorus and magnesium products are often given by slow intravenous injection, and more can be given subcutaneously or intraperitoneally , which means into the body. 


Veterinarians will often listen to the heart, so administration can be quickly slowed or stopped if problems occur. 


We want to treat clinical cases when they occur, but we also want to prevent further cases from developing by getting much needed magnesium into the cattle. 


Force feeding or drenching with magnesium oxide may prevent further cases if we also start supplementing with a good mineral program containing magnesium. 


Good trace minerals will have macro minerals such as calcium, phosphorus and magnesium, as well as many micro minerals such as copper and zinc. 


Some producers are misled by terms such as trace mineralized salt, which is primarily micro minerals with salt to enhance consumption. 


These products don’t have macro minerals and are much cheaper.


Read the label when buying minerals to ensure the product has macro minerals. 


Mineral programs are absolutely key to preventing this sudden killer of cattle.


Pastures in some regions provide inadequate magnesium, and supplementation must be greater than the standard. 


However, palatability is a problem if levels become too high, and cattle may back off mineral consumption. 


Producers should work with a veterinarian and nutritionist or feed mill to make sure they have adequate amounts of macro minerals in their program. 


As well, they should keep a close eye on cattle in times of stress. 


Not all cattle will eat adequate amounts of minerals, even though it is available for them.


Supplying good quality minerals can prevent grass tetany as well as other mineral deficiencies.

Roy Lewis works as a technical services veterinarian part time with Merck Animal Health in Alberta.