24-04-2025
Be alert to the risk of grass tetany
HERD HEALTH SERIES: Maura Langan, Commercial and Technical Manager (Large Animal) at Norbrook
Maura Langan, Norbrook Veterinary Advisor
Grass tetany or staggers is a metabolic disease caused by an acute deficiency of magnesium (hypomagnesaemia). Lactating cows, especially those that are newly calved, have an increased requirement for magnesium. Most supplementary feeds will include adequate supplies of magnesium, but suckler cows and store cattle are rarely supplemented at grass and as such they may experience grass tetany.
Cattle are unable store this essential mineral and have no active hormonal control of magnesium levels in the body, so they are reliant on daily dietary intake. Magnesium levels in pasture can vary quite considerably. The application of fertilisers containing nitrogen and potassium interferes with the uptake of magnesium by the grasses reducing the availability for cattle.
Rapidly growing spring grass (especially rye grasses) is therefore low in magnesium, this is typically seen when a warm dry spell is followed by rain. Spring grass is also much lower in fibre which increases the rate of transit through the rumen, reducing magnesium absorption rates and causing scour.
Poor weather, often a sudden cold and wet spell, is often associated with cases of grass tetany as cattle stop grazing and magnesium intake is further reduced.
Clinical Grass Tetany is a rapid onset metabolic disease and a true veterinary emergency. Clinical signs include restlessness, hyper-excitability, 'wild eyes', frothing at the mouth, incoordination, staggering, collapse and seizures. Treatment needs to be instigated as soon as clinical signs are noticed, as animals will rapidly deteriorate and in severe cases death can occur within one hour of first symptoms.
Emergency veterinary treatment is required with intravenous administration of a calcium and magnesium solution (Calciject 40+3) at first sign of symptoms. A further follow-up treatment of Magniject should be administered subcutaneously. Animals should not be stimulated during treatment.
As with other metabolic conditions, animals that display clinical signs are only the tip of the iceberg and much of the herd is likely to be sub-clinically affected. Preventative measures via oral supplementation of magnesium are the simplest and most cost-effective option in managing grass tetany. Magnesium salts and minerals can be unpalatable.
Mineral licks can be unreliable as individual intakes cannot be guaranteed.
The optimum way of ensuring supplementation is through administration of a sustained release magnesium bolus. Opti-Mag3 bolus provides 100g of slow-release magnesium. Administration of two boluses 2-3 days before the risk period will supply approximately 6g of magnesium per animal per day for four weeks.
