Grass tetany is a highly fatal disease associated with low levels of magnesium in the blood. Grass tetany can affect all classes of cattle, but older cows with calves on their side during late winter and early spring are most at risk. Cattle store magnesium in their bones and muscles but cannot readily access and use these stores when needed. The animal constantly loses magnesium in urine, feces and milk, so when grazing lush green magnesium-deficient grass, cattle need magnesium supplements to meet daily requirements. A cow in peak lactation at 6–8 weeks following calving needs a constant source of magnesium to replace the large amount lost from the body in milk. Some causes of grass tetany are the lower magnesium levels in cool-season grasses and legumes, higher moisture content in grass, low intake of phosphorus among other things.
Animals suffering from grass tetany are often found dead. There may be signs of struggle on the ground beside the animal, which indicate they were leg paddling before death. Early signs include some excitability with muscle twitching, an exaggerated awareness and a stiff gait. Animals may appear aggressive and may progress through galloping, bellowing and then staggering. In less severe cases, the only signs may be a change in the character of the animal and difficulty in handling.
Blood magnesium levels must be restored. Veterinary administration of an intravenous calcium and magnesium solution produces best results. However, in acute cases where time is critical, producers can administer an Epsom salt solution via an enema while waiting on the veterinarian.
Producers should also provide oral sources of magnesium to affected herds to prevent relapses. These include a high magnesium content mineral, fed free choice during any period of potential grass tetany.
The goal of a well-managed prevention program should aim to eliminate factors, which reduce magnesium absorption and provide a magnesium supplement. Provide good-quality hay or silage to increase energy and roughage intake. Pellets or grain can be added but must be introduced carefully. Provide salt if a source is not available.
Prevention is the best policy where possible. It is a good idea to move lactating cows – especially older animals – to high legume and high dry matter pastures and provide good quality magnesium supplements through a high magnesium mineral.
Long-term management includes correcting soil acidity with lime, plant clovers and apply a phosphate fertilizer. Limit potash and nitrogen application until soil acidity is corrected and clovers are established. Keep good records to identify repeat offenders. Some cattle are more susceptible than others, so identification and supplementation of magnesium may head off problems before they happen.
For more information, contact the UT-TSU Extension Office in Wilson County at 615-444-9584. You can also find us on Facebook or visit extension.tennessee.edu/wilson. Ruth Correll, UT Extension-TSU Cooperative Extension agent in Wilson County, may be reached at 615-444-9584 or email@example.com.