Why grass tetany is an emergency

A cow down or with suspected grass tetany needs prompt action to save its life. It is suffering from low blood levels of magnesium – a mineral vital to nerve function. Poor nerve function arises from low magnesium levels. This is what leads to muscle tremors and seizures. Death usually occurs when the heart muscle fails. If you are standing beside a cow in this state, you can often hear a rapid and loud heartbeat.

When standing, these cows appear to have nervous symptoms. They may be staggering, frothing from the mouth and can be quite aggressive. When they go down, usually to one side, they will have aggressive seizures and shaking. To make a conclusive diagnosis on dead animals, we can test the vitreous fluid of the eye for magnesium levels to rule it in or out as the cause of death.

In the springtime, I routinely advised farmers to give a bottle of magnesium under the skin to any freshly calved cow acting peculiarly or with nervous symptoms at grass. It is important to monitor closely and seek veterinary advice if no improvement is seen.

Why does it occur?

Cattle can’t store much magnesium in their bodies except in their bones and they only mobilise it very slowly. So when the daily intakes drop below the required levels, you can get a deficiency. This can also occur with lactating ewes. Animals such as cows and ewes that are milking use and lose more magnesium in their milk.

This is why we see more of a risk at this time of year, but it can affect animals in the autumn as well. Rarely, you can see it in young calves on milk replacer with low levels of magnesium but it is usually complicated by them scouring or sick. Cattle need daily intakes of magnesium as they can’t store much of it in their bodies.

What affects intake?

Intakes can be affected in two ways – by either low levels in the forage consumed or not enough absorption of the magnesium. Factors such as adverse weather, stock outdoors or any other stressor can limit intakes in spring. It can also be a risk in suckler cows that have calves weaned off them. Cows in heat can sometimes be less likely to eat and a change in cows’ diets can also affect intake.

Rapidly growing spring grass can be low in magnesium, while lush grass can have increased transit times which may affect magnesium intakes and absorption. High-potassium applications on pasture will also potentially lock up magnesium and reduce its absorption, greatly increasing the risk of grass tetany. Heavy nitrogen application will potentially speed up grass growth and lower absorption of magnesium. This is why in spring – with lush grass and cows and ewes out – we are in the peak risk period for this condition.

Treatments

Remember, time really is of the essence with these cases, but farmers should be careful with cows as this condition can make them extremely nervous if they are still standing. These cows can be very unpredictable and even dangerous. When cows are down and tremoring, they can also be very reactive and with legs flailing great care should be taken to avoid injury. Often, your vet will choose to sedate the animals before administering magnesium treatments.

We never give magnesium solutions into the vein. Instead, we promote slow absorption by administering them under the skin. Always warm the bottle of magnesium sulphate slowly before administering it to speed up absorption. We often give a bottle of calcium intravenously along with his treatment.

Your vet may administer tiny amounts of magnesium intravenously slowly, so if waiting for the vet, administer one bottle of magnesium under the skin.

When cows respond to treatment they should get up rapidly in one to two hours. If cows are staying down, the most likely thing is secondary injury from being down. These cows should be moved to a comfortable area and given pain relief.

Ewes will generally receive 80ml to 100ml of magnesium sulphate under the skin and respond well to that treatment.

Prevention is key

We know a lot of the risks at herd level around grass tetany. These risks also feed directly into preventing grass tetany. Most people will know that we are now in the peak time for grass tetany on our farms. While prevention is key, never let the medicine cabinet be without a bottle of magnesium sulphate or two.

Short-term actions after a case of grass tetany

Top tips for prevention

1 When feeding concentrates this spring, ensure they are high in magnesium as this is a great way of ensuring cattle and ewes have enough magnesium intakes.

2 Where cows get very lose and grass growth is very good, I recommend feeding a small amount of fibre to slow down gut transit times. This may mean supplementing with some hay, straw or silage at pasture.

3 Increasing pasture clover levels is thought to increase the amount of magnesium available in the plant.

4 Avoid grazing pastures that have had heavy slurry application or recent nitrogen application within the last three to four weeks.

5 Perform pasture dusting with calcined magnesite or magnesium oxide at peak risk times. Lime application also helps, not only to raise pH but also magnesium levels in pasture.

6Where significant risks are present, apply two oral magnesium boluses pre-grazing. This will give six to eight weeks of cover during the risk.

7 Avoid any sudden changes to the diet, unnecessary transport and provide shelter from adverse weather. This could mean that a high hedge is worth its weight in a rough spring night.