If you’ve ever seen a cow suddenly collapse in early spring, seemingly out of nowhere, you might have witnessed a case of grass tetany. This metabolic disorder, historically linked to magnesium deficiency, can be a problem for cattle grazing lush cool-season grasses. Understanding the causes, symptoms, and prevention strategies of grass tetany can help cattle producers manage their herds effectively and avoid costly losses.
What is Grass Tetany?
Grass tetany, also known as grass staggers, is caused by low levels of magnesium (Mg) in the blood. It is most commonly observed in lactating cows grazing early spring growth of cool-season grasses like tall fescue. These pastures, while high in energy and protein, often contain low magnesium levels and excessive amounts of potassium (K), which can interfere with magnesium absorption.
Environmental stressors such as frost and drought further alter the mineral composition of forages. Spring-calving cows are especially vulnerable due to the high magnesium demands of lactation, which can quickly deplete their reserves.
Recognizing the Symptoms
Grass tetany doesn’t always announce itself with clear warning signs but knowing what to look for can make the difference between saving and losing an animal. Early symptoms include:
- Increased excitability
- Teeth grinding
- Excessive salivation
- Muscle spasms
- Loss of body control
- Collapse and death in severe cases
Without immediate intervention, death can occur within hours.
Traditional Solutions: Do They Work?
For years, the standard recommendation has been to supplement cattle diets with additional magnesium. Magnesium oxide is commonly added to mineral mixes or mixed into feed to increase intake. However, this approach has limitations. Magnesium supplements are often unpalatable, leading to inconsistent intake among cattle. Additionally, despite supplementation, some cases of grass tetany still occur, indicating that other factors are at play.
In acute cases, intravenous magnesium and calcium solutions administered by a veterinarian can treat the condition. However, prevention remains the best approach since once symptoms become severe, survival rates decline significantly.
The Role of Potassium and Sodium in Grass Tetany
Research suggests that potassium and sodium (Na) play a crucial role in magnesium absorption, and their balance in forages may be as important as magnesium itself.
Potassium: The Hidden Culprit
While potassium is an essential mineral for plant growth, high levels in pastures can exacerbate magnesium deficiency. Potassium competes with magnesium for absorption sites in the rumen, meaning that even when magnesium levels in forage are adequate, excessive potassium can block magnesium from leaving the rumen, increasing the risk of grass tetany.
Fertilization practices can further contribute to the problem. Heavy potassium fertilization, especially in early spring, may inadvertently increase the risk of grass tetany by skewing the mineral balance in pastures.
Sodium’s Overlooked Role
Sodium plays a less obvious but equally important role in magnesium absorption. Sodium helps transport magnesium across the rumen wall, improving its availability to the animal. However, freeze-damaged grasses often lose significant amounts of sodium, potentially reducing magnesium uptake even further.
Low sodium intake in cattle diets can compound the issue. Providing free-choice salt (sodium chloride) or increasing the amount of salt in your free-choice mineral can support magnesium absorption and serve as a cost-effective strategy for reducing the risk of grass tetany.
What About Phosphorus?
Soil phosphorus may play a critical role in preventing grass tetany in ruminants. Research from the University of Missouri indicates that fertilizing tall fescue pastures to reach adequate soil phosphorus levels enhances the availability of magnesium (Mg) in the forage.
This improvement in magnesium availability helps ruminants maintain proper magnesium levels in their diets, which is crucial for preventing grass tetany. Consequently, ensuring sufficient phosphorus in the soil can significantly reduce the risk of this potentially dangerous condition for livestock.
Prevention Strategies for Cattle Producers
Managing grass tetany requires a multi-faceted approach. Here are some key strategies to consider:
- Provide High-Magnesium Supplements: Ensure cows receive sufficient magnesium, especially during high-risk periods in early spring. Most “hi-mag” minerals will contain between 6-10% magnesium.
- Increase Salt Consumption: Most mineral supplements will contain between 15-30% salt. Choose a mineral that is closer to 30% salt if possible. If not, consider mixing a bag of salt and a bag of mineral for cows in March and April.
- Limit Excessive Potassium Fertilization: Be mindful of pasture fertilization practices. Avoid heavy applications of potassium in early spring, as this can suppress magnesium absorption in cattle.
- Graze Mixed Pastures: Introducing legumes such as clover into pastures can help balance mineral content, as they generally contain higher levels of magnesium compared to grasses alone.
Conclusion
Grass tetany remains a significant challenge for cattle producers, but with careful management and strategic supplementation, its impact can be minimized. Understanding the interplay between magnesium, potassium, and sodium in forage systems is key to developing effective prevention strategies. By staying informed and proactive, producers can protect their herds and ensure the health and productivity of their cattle during the critical early grazing season.
~ Drs. Harley Naumann and Eric Bailey, MU Extension
The Alliance for Grassland Renewal is a national organization focused on enhancing the appropriate adoption of novel endophyte tall fescue technology through education, incentives, self-regulation and promotion. For more resources or to learn more about the Alliance for Grassland Renewal, go to www.grasslandrenewal.org
The Alliance for Grassland Renewal 