Grass Tetany: The “Silent Killer” Caused by Magnesium Metabolism Disorder

1. Etiology

The core pathogenesis is insufficient magnesium intake and absorption, with serum magnesium concentration falling below 0.5 mmol/L (normal range: 0.7-1.0 mmol/L). Multiple contributing factors include:

• Low magnesium content in forage

Spring green gramineous forage contains only 0.10%–0.18% magnesium. High potassium and nitrogen levels inhibit magnesium absorption, while high moisture shortens the duration available for magnesium uptake.

• Poor soil conditions

Acidic soils readily fix magnesium ions, and excessive application of nitrogen and potassium fertilizers exacerbates the “potassium-induced magnesium antagonism” effect.

• Physiological characteristics of cattle

Cows at peak lactation have high magnesium excretion, and cows older than 5 years show reduced magnesium absorption, resulting in higher susceptibility.

• Inappropriate feeding and management

Overgrazing, sudden turnout to pasture, and stress responses further aggravate magnesium deficiency.

2. Impacts on Cattle

Acute cases have a rapid onset and a mortality rate exceeding 80%, with clinical signs including muscle tremors, limb convulsions, heart failure, and death by asphyxiation. Although subacute and chronic cases have lower mortality, they lead to reduced feed intake, a 10%–20% drop in milk yield, a 15%–20% decrease in conception rate in breeding cows, and lowered immunity, increasing the risk of infectious diseases. Overall, the comprehensive breeding efficiency of affected pastures can decrease by 20%–30%, imposing a heavy economic burden on producers.

3. Integrated Control Strategie

Following the principle of “prevention first, integrated management”, the key is to ensure adequate magnesium intake and absorption:

• Agronomic measures

Apply magnesium fertilizer (20-50 kg/ha) before spring forage regreening; maintain a nitrogen-potassium-magnesium ratio of approximately 10:5:1; amend acidic soils and optimize forage composition.

• Feeding management

Supplement magnesium preparations 2-3 weeks before grazing, ensuring a daily magnesium intake of 30-70 g per head (increased for lactating cows); implement rational grazing systems and reduce stress.

• Clinical treatment

Administer intravenous magnesium calcium combination preparations for acute cases, and oral magnesium sulfate for subacute cases. Continue magnesium supplementation for 1-2 weeks after recovery.

• Monitoring and early warning

Regularly test magnesium levels in forage and cattle serum, and intervene promptly when abnormalities are detected.

4. Conclusion

Grass tetany occurs frequently in spring grazing cattle herds and is closely related to forage, soil, animal physiology, and management practices, with severe detrimental effects.

Reasonable magnesium supplementation, optimized agronomic and feeding management, and scientific monitoring can effectively reduce the incidence. In the future, supported by technologies such as forage breeding, more efficient and green prevention and control strategies are expected to be developed, promoting the healthy development of the cattle industry.