with Phil Rennie
New Zealand’s fast-growing spring pastures are traditionally low in magnesium and it is this lack of magnesium that can enhance the disease hypomagnesaemia, also known as grass staggers. This can occur when animals are grazed on lush grass or fed green cereal crops.
Adult lactating cows are most susceptible to the disease due to loss of magnesium through the production of milk.
Soils that are naturally high in potassium and those fertilised with potash and nitrogen are high-risk areas for cows to develop hypomagnesaemia. Low blood magnesium levels interfere with nerve activity throughout the body, causing general weakness, loss of appetite, and eventually brain dysfunction.
An early sign of grass staggers is cows may appear to be grazing normally then suddenly throw their heads in the air, bellow and run blindly around the paddock. They start twitching, are nervous, may have staring eyes and stiff movements and may also urinate frequently.
They can be dangerous to people and other stock as these signs progress. Ultimately they become unsteady on their feet and once down, spastic movements develop with the head often moving up and down incessantly with a lack of muscle control. Respiration is rapid and laboured. Left untreated the cow will die in a short period of time.
This disease should be treated as an emergency and immediate treatment to restore blood magnesium levels is crucial. An intravenous injection of a metabolic solution containing magnesium is required, sometimes with the aid of a sedative to be done safely. Guidance is recommended for inexperienced people who are using jugular vein access and a vet should be called upon to assist. This step must be done slowly as the condition of the heart and brain is vulnerable at this stage.
The simple magnesium sulphate 20 per cent solution (yellow bag) can be safely given under the skin as a follow up supportive treatment. Full recovery may take several hours as the magnesium balance is restored to normal levels in the brain tissue.
Once the cow has the swallow reflex it is important to maintain the blood magnesium levels for at least the next two to three days to guard against a relapse, which can be done with an oral magnesium supplement.
Magnesium oxide powder or a similar magnesium enhancing supplement should be given to cows prior to calving to help to prevent hypomagnesaemia developing. Supplementing magnesium can also be of benefit in itself with an increase in milk production expected.
If the combination of magnesium infusions followed by oral magnesium is not enough to get the cow back on her feet then it is probably more than a case of simple grass staggers. It’s best to contact your local vet to assess the cow for any other reason/s she is unable to recover.