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What is Grass Tetany?

Grass tetany is a condition found mainly in cattle; however, horses have been found to suffer from this as well. Hypomagnesemic tetany is another term for grass tetany, which describes the condition as a decrease in the intake of magnesium and calcium coupled with an increase in potassium. Other types of hypomagnesemic tetany are lactation tetany, milk tetany, transport tetany, and wheat pasture tetany.

A horse experiencing grass tetany may exhibit tremors and lack of coordination. Excess nitrates and inadequate sodium are two contributing factors to grass tetany; mineral balance is essential to the well being of your equine.

Grass tetany is a condition that your horse may experience due to a magnesium deficiency. This deficiency occurs most often due to factors in the pasture where your horse forages such as rapidly growing, lush young grass in the spring and the effects of frost and other environmental factors in the fall.

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Symptoms of Grass Tetany in Horses

The symptoms your horse may experience can vary greatly between mild and severe. If left untreated or unnoticed, grass tetany can result in death. 

  • Gait issues 
  • Lack of coordination
  • Convulsions – Your horse may begin to thrash around violently 
  • Coma – Horses are often found unconscious with no obvious signs or symptoms prior 
  • Muscle stiffness – Tail clamping and an overall stiffness to his muscles 
  • Your horse’s mouth remains closed with difficulty opening 
  • Grinding of the teeth
  • Eyes – May be bloodshot and rolling around in his head
  • Throwing his head back
  • Change in behavior – You may notice he is becoming more irritable and he has an increased sensitivity

Causes of Grass Tetany in Horses

  • Changes to grass make up in frosts/freezes 
  • Early spring, lush grass may be too rich in protein
  • Autumn to early winter may see elevation of nitrate and potassium in the grass
  • Drought breaking rains
  • Stress from transport; the horse does not consume enough food
  • Low magnesium content in the forage
  • Lack of adequate grazing opportunities due to weatherr
  • Believing your horse receives enough minerals via his salt blocks and feeds
  • High protein feeds
  • Not providing your horse with enough variety of minerals or salt in his diet
  • Using fertilizer that is high in potassium can result in an increased risk of your horse developing grass tetany

Diagnosis of Grass Tetany in Horses

The veterinarian may discover through blood testing that your horse is experiencing low magnesium and low calcium; documentation shows that 80% of grass tetany cases present these blood result markers. Other mineral levels may be analysed in a urinalysis and electrolyte balances may reflect excess nitrate and potassium. 

The veterinarian will assess the clinical signs of your horse and will want to discuss the typical diet and foraging opportunities of your horse’s daily regimen as well as his access to free salt. An examination of the hay and a walk about the pasture can rule out plant toxicities which may present similarly. Other conditions may be ruled out also such as metabolic diseases and secondary immune suppression.

Treatment of Grass Tetany in Horses

Treatment for grass tetany will vary and prevention of the condition is a primary focus. Treatment will include stabilizing your horse while providing supportive measures. Stabilizing his mineral levels may be accomplished through intravenous. Sodium, calcium and magnesium levels will need to be normalized.  Your veterinarian may suggest a solution containing 25% calcium borogluconate and 5% magnesium hypophosphite which has been shown to be adequate treatment for cattle. Injections of Mg can also be used in conjunction with the solution. MgCl enemas can be administered by you as well at home.

Recovery of Grass Tetany in Horses

Your veterinarian will suggest follow up appointments as needed. A large part of ensuring no further issues occur will be making necessary changes to your horse’s diet (such as not overfeeding protein) and environment (ensuring free minerals and salt are available). Having a space to keep your horse away from new grass can be an essential part of preventing further concerns. Providing clean, dry hay at all times will also encourage him to not eat as much grass. Avoid the overuse of fertilizers rich in nitrogen to reduce the risk as well.