5. Grass tetany (hypomagnesemia)
Various disorders in cows go hand in hand with aberrant behaviour, or in other words, neurological symptoms. One disorder that involves neurological symptoms is mad cow disease, which gained much publicity a number of years ago because the impression was that the disease could be transferred to humans. Another disease that involves aberrant behaviour is grass tetany. Animals suddenly experience cramps; they collapse, they thrash wildly with their legs and head and they moo loudly. Without immediate action, they will die within a few hours.
Grass tetany in cows is the result of a nutritional error: if cows go without enough magnesium for too long, it can suddenly go to their head. A magnesium shortage in grass comes about if the soil contains too little of the mineral magnesium and too much potassium. Potassium displaces magnesium in its absorption in grass. This process does not hinder the growth of grass, the grass is simply not as green. But that is not noticeable if the colour of the grass in the pasture is the same everywhere. Grass tetany only occurs in cows that almost exclusively eat grass with a low magnesium content, meaning in pasture day and night. Modern dairy cows no longer go outdoors, or only a few hours a day. They are given a sophisticated ration of grass, corn and various types of concentrates. They need that to be able to produce fifty litres of milk or more per day. That is not possible on a diet of grass alone.
It is November. A call comes in regarding a cow with grass tetany. That is a call of the utmost urgency. I quickly hang up and trot off to the car. Then the quickest way to the pasture concerned. There is not a minute to spare. It is cheerless autumn weather with lash rain and poor visibility despite the windscreen wipers. Fortunately, traffic is very light on the local roads. There are no cows to be seen, as they are all already inside. Except here, where they huddle together in front of the gate with their backs to the wind and rain, resigned to waiting for the shower to end.
with their backs to the wind and rain
A cow is lying on its side in the pasture. The legs are thrashing wildly; the head is pounding on the soil; she is foaming at the mouth and she is roaring anxiously. I quickly fetch two drips from the car, along with a hose and a needle. A stethoscope in my pocket; jump the gate, past the herd of cows. Quickly! The only safe place in the vicinity of the cow is her back side. From there, I insert the needle into the milk vein below the belly. I ignore the mud on the skin. Keeping the drip high, no air in the hose and the life-saving fluid with magnesium salts flows into the blood, on its way to the heart, the brain and the muscles. The first bottle is empty within five minutes. As I am hooking up the second bottle, the cramping appears to be diminishing somewhat. I hold the second bottle lower to reduce the speed of the drip and I check the animal’s heart. It is pounding against the stethoscope. But the rhythm is gradually slowing down. This was just in time.
I recommend that the cows be stalled. They all have an inadequate reserve of magnesium and so they are at risk of developing grass tetany sooner or later. My recommendation falls on stony ground: the farmer looks past me towards the pasture. The animals have been out here for only a week and there is still lots of grass, whereas the winter stocks will need to be drawn on if the animals are indoors. I ask how he fertilized this plot. “The usual, liquid pig manure.” Pig manure contains lots of potassium. And so it is essential to scatter extra magnesium. “Did you also use kieserite or magnesium nitrate fertiliser?” He is clearly annoyed: “Can’t you see how fast the grass is growing here!” I have offended his pride as a farmer: like he doesn’t know how to fertilise the soil! I keep my thoughts to myself. They are his cows, after all.
A few days later, a colleague on call is summoned to examine a second cow with grass tetany in the same pasture. The cow is already dead when he arrives. Shortly afterwards, all of the cows have been stalled.
Nowadays, as cows spend only a limited time at pasture, grass tetany no longer occurs. Still, the risk is not entirely absent. The ration of cows fed in stalls can consist mainly of grass. And cows that produce large amounts of milk lose a lot of magnesium every day with the milk. The balance between intake and release can become disrupted if the grass that they are fed indoors does not contain enough of this mineral. Should grass tetany manifest itself in stalled cows, it is to be hoped that the symptoms are immediately recognised, as the condition is fatal if an adequate reaction is too long in coming.
© Leo Rogier Verberne