Hypomagnesemic Tetany
Understanding Hypomagnesemic Tetany in Cattle: Prevention, Diagnosis, and Treatment
As spring approaches in Rustenburg, the green pastures look lush and inviting. While this growth is a boon for grazing, it also brings a hidden risk for cattle: hypomagnesemic tetany, also known as grass tetany. This acute neurological condition can strike suddenly, especially in lactating cows grazing on green pastures or cereal crops, and if left untreated, it can be fatal.
Understanding the causes, signs, and prevention strategies is essential for every cattle farmer.
What is Hypomagnesemic Tetany?
Hypomagnesemic tetany occurs when a cow’s blood magnesium levels drop below the level required to maintain normal body functions. Magnesium is essential for nerve and muscle function, and when it becomes deficient, cattle can experience severe neurological symptoms, including muscle twitching, seizures, and even sudden death.
Typically, this condition affects lactating cows because their magnesium needs increase significantly to support milk production. It can also affect calves, especially those fed only milk or milk replacer, and sheep under similar conditions.
Why Does It Happen?
Several factors can contribute to hypomagnesemic tetany:
Low magnesium intake from pasture – Short, rapidly growing grass often contains less than 0.2% magnesium, which is insufficient for cows, especially during lactation.
High potassium and nitrogen in the soil – Soils fertilized with potash or poultry manure can reduce magnesium absorption in cattle.
Environmental stress – Cold, windy weather, reduced feed intake, transport, or sudden changes in pasture can trigger the condition.
Hypocalcemia – Low calcium levels can worsen the effects of magnesium deficiency. Lush green pastures and cereal crops can reduce available calcium in the blood, compounding the problem.
In short, even if the grass looks healthy, the mineral content may not meet the nutritional demands of your herd.
Recognising the Clinical Signs
Early detection is crucial. In severe cases, cattle may seem normal one moment and suddenly:
Throw up loudly
Gallop frantically, sometimes appearing blind to their surroundings
Fall and have violent paddling seizures, frothy salivation, and eye tremors
Less severe cases may show warning signs days before an acute episode:
Muscle twitching in the face, shoulders, or flank
Stiff walking and hypersensitivity to touch or sound
Frequent urination
Rapid heartbeat and elevated body temperature due to muscular activity
Calves show similar symptoms, often triggered by magnesium-poor milk or milk replacers, especially if combined with chronic scours.
Diagnosing Hypomagnesemic Tetany
Diagnosis usually involves:
Observation of clinical signs – Rapid onset of seizures and convulsions is highly indicative.
Response to treatment – Cows that recover quickly after magnesium administration confirm the diagnosis.
Laboratory tests – Measuring magnesium levels in blood, urine, cerebrospinal fluid, or vitreous humor can provide definitive confirmation.
Normal magnesium levels in cattle range from 1.8–2.4 mg/dL, while tetany typically occurs below 1.2 mg/dL. Concurrent low calcium levels often accompany magnesium deficiency.
Treatment:
Acting Quickly Saves Lives
Hypomagnesemic tetany is an emergency. Immediate action can save affected animals:
Intravenous magnesium – Administer magnesium sulfate slowly IV, often combined with calcium borogluconate.
Subcutaneous magnesium – Additional magnesium can be given under the skin if needed.
Minimise stress – Avoid stimulating the cow during treatment, as excitement can trigger fatal seizures.
Follow-up feeding – Provide hay top-dressed with magnesium oxide (around 60 g per cow per day) to prevent recurrence.
Rapid intervention often results in recovery within minutes to hours.
Prevention: The Best Strategy
Since cattle cannot store magnesium efficiently, daily supplementation is critical:
Oral magnesium supplements – Provide magnesium oxide mixed with molasses, concentrates, or hay.
Magnesium-enriched fertilizers – In certain soil types, fertilizing pastures can increase magnesium content.
Slow-release magnesium devices – Administered intraruminally, these provide a steady supply of magnesium over time.
Supplementary feeding – Out-wintered stock or herds on lush cereal crops should have access to hay and additional feed.
Regularly monitoring pasture composition, soil mineral content, and animal health is essential for prevention.
Special Considerations for Calves
Calves between 2–4 months old are particularly vulnerable, especially if:
They are fed milk only or milk replacer
They suffer from chronic scours
Their diet lacks sufficient magnesium
Treatment involves subcutaneous magnesium injections and oral supplementation. Prevention includes providing good-quality legume hay and starter rations from as early as two weeks old.
Key Takeaways for Rustenburg Farmers
Hypomagnesemic tetany is sudden, severe, and preventable.
Green pastures and cereal crops can create a false sense of security, masking magnesium deficiency.
Early recognition, rapid treatment, and daily supplementation save lives.
Monitor soil, pasture, and herd health to reduce risks, especially during spring and early summer.
By staying vigilant and proactive, cattle farmers in Rustenburg and the Northwest Province can safeguard their herds from this dangerous condition.
Preserving Heritage, Ensuring Future Prosperity
As we celebrate the Ankole breed’s balanced frame and exceptional bodily proposition, it’s essential to recognize the role of conservation efforts in safeguarding this heritage breed. Ankole cattle are not only a source of economic prosperity but also cultural significance, deeply rooted in the heritage of the regions they inhabit.
Cultural Significance:
Ankole cattle are more than livestock; they are cultural icons.
Their distinct appearance, characterized by the iconic long, curved horns, carries cultural and historical significance.
Preserving the Ankole breed is not just an agricultural imperative but also a commitment to safeguarding cultural heritage.
Sustainable Farming Practices:
The balanced frame and good bodily proposition of Ankole cattle align with the principles of sustainable farming. Their adaptability to diverse environments and their efficient feed utilisation contribute to the promotion of eco-friendly and sustainable agricultural practices. As the global agricultural landscape emphasizes sustainability, the Ankole breed emerges as a valuable ally in this endeavor.
Genetic Diversity:
Conserving Ankole cattle ensures the preservation of genetic diversity within the cattle population.
This is vital for the overall resilience of the global cattle industry.
By maintaining diverse breeds like Ankole, farmers contribute to the health and adaptability of the broader genetic pool, mitigating risks associated with disease and environmental changes.
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