Grass tetany continues to be a major cause of death in cows, particularly suckler cows, in Northern Ireland. It is caused by magnesium deficiency, which is common in lactating cows grazing lush spring pasture. A sudden deterioration in weather condition scan lead to severe outbreaks of grass tetany by dramatically increasing the number of cows deficient in magnesium. Therefore farmers need to be aware of the risks and take steps to prevent this disease, particularly during spring and autumn.
Animals with grass tetany become nervous and excitable. They may show muscular twitching or walk with a staggering gait. They may quickly go down, develop convulsions, become comatose and die. Because of the short duration of clinical signs, affected animals are frequently found dead. Most cows that develop clinical grass tetany will have shown suspicious signs within the preceding few days. These signs include a drop in milk yield, loss of condition and a change in temperament.
Magnesium deficiency alters calcium metabolism and thereby increases the risk of “milk fever” in recently calved cows at grass in spring (and especially in autumn). A clinical case of grass tetany usually represents “the tip of the iceberg” as many other cows in the herd are likely to be severely magnesium-deficient. Therefore, providing increased magnesium supplementation of the remainder of the herd is also important.
Because of the high mortality associated with grass tetany prevention is essential. It is based on providing additional magnesium in the diet and reducing other risk factors. Cows cannot mobilize magnesium from body stores and therefore need a continuous daily supply of 30g of magnesium/cow/day equivalent to 60g or 2oz of calcined magnesite/cow/day) especially during spring and autumn.
Supplementation may also be carried out using using any of the following pasture dusting, administration of bullets/boluses, addition of Magnesium to water, free access blocks or molasses with added calcined magnesite.
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