Grass tetany, often referred to as wheat pasture poisoning, is a metabolic disorder that primarily affects grazing cattle during the early spring months. This condition is triggered by a critical deficiency of magnesium in the bloodstream, a mineral that is essential for proper nerve function and muscle contraction. The disorder is notoriously sudden in onset, making it a significant concern for livestock producers who rely on cool-season grasses for forage.
Understanding the Biological Mechanism
The root cause of grass tetany lies in the imbalance between potassium and magnesium within the rapidly growing grass plants. As the soil warms in early spring, lush, fast-growing forage shoots up. These new growths are naturally high in potassium and nitrogen but struggle to accumulate sufficient magnesium. When livestock consume large quantities of this nutritionally skewed grass, the magnesium absorption in the rumen is inhibited, leading to a swift drop in blood magnesium levels and subsequent neurological failure.
Primary Risk Factors for Livestock
Not every animal grazing on spring grass will succumb to tetany, but specific risk factors dramatically increase the likelihood of an outbreak. Producers should be particularly vigilant if their herd includes older, lactating cows, as they are most susceptible due to the magnesium demand of milk production. Other risks include lush pastures of immature grass, high nitrogen fertilizer application, and soil types that are acidic or sandy, which leach magnesium away from the root zone.
Recognizing the Clinical Signs
Time is of the essence when dealing with a potential tetany outbreak, as the progression from grazing to death can occur in a matter of hours. Acute symptoms are primarily neurological and highly distressing to witness. Key indicators include extreme irritability, muscle tremors or twitching, staggering gait, and a characteristic "sawhorse" stance where the animal appears stiff-legged. As the condition worsens, the animal may collapse, grind its teeth, and experience convulsions before succumbing to respiratory failure.
Preventative Nutritional Strategies
Prevention remains the most effective strategy against grass tetany, and it begins long before the first grazing season. Supplementing the diet with magnesium oxide is the standard approach, typically administered through loose minerals or mixed into feed. However, simply providing a mineral block is insufficient; the sodium content must be adequate to encourage consumption, as salt intake drives thirst and increases mineral uptake.
Treatment and Emergency Response
If an animal is observed displaying symptoms of grass tetany, immediate action is required to prevent death. The treatment of choice is an intravenous injection of magnesium sulfate, commonly known as Epsom salts. This must be performed by a veterinarian or a highly trained individual, as improper dosing or speed of injection can be fatal. Oral magnesium supplements are generally ineffective in an emergency because the animal’s digestive system is likely not functioning properly to absorb the mineral.
