Grass Tetany in Stocker Cattle: A Complete Overview

With snow covering much of the United States, it is hard to picture lush green grass. However, that snow’s moisture and sunshine will generate lush green grass before we know it. That grass could eventually lead to challenges, including grass tetany.  

Grass tetany, also known as grass staggers or hypomagnesemia, is a metabolic disorder commonly affecting stocker cattle grazing on lush, rapidly growing pastures. This condition occurs when blood magnesium levels drop to critically low levels, leading to neurological symptoms and, if untreated, potentially fatal outcomes. Understanding the causes, symptoms, prevention and treatment of grass tetany is crucial for cattle producers seeking to maintain the health and productivity of their herds. 

Cattle Nutrition Experts  

Curious about who you’re getting advice from? Gain Smart® is a brand of mineral supplements that enhances cattle health, optimizes growth and improves feed efficiency. Our products support commercial producers looking to maximize their operations nationwide. Best of all, Gain Smart products ensure balanced nutrition for livestock—and as all producers know, a healthy animal is a better-performing animal. 

The Gain Smart brand is developed by BioZyme® Inc., the makers of VitaFerm, a leading fermentation company pioneering advancements in animal nutrition and health. Through innovative research and high-quality manufacturing, BioZyme creates powerful solutions that improve animal performance and support producer profitability in the agricultural industry.  

Our mission: undeniable positive impact on the health and wellness of your animals and your business.  

Symptoms of Grass Tetany 

The clinical signs of grass tetany can vary depending on the severity of magnesium deficiency. Symptoms are typically categorized into early, advanced and terminal stages: 

Early Symptoms: 

• Restlessness and nervousness 
• Reduced appetite and reluctance to graze 
• Stiff or awkward gait 

Advanced Symptoms: 

• Muscle twitching and tremors 
• Increased excitability and sensitivity to external stimuli 
• Rapid breathing and elevated heart rate 
• Staggering or uncoordinated movements 

Terminal Symptoms: 

• Inability to stand 
• Convulsions and kicking 
• Coma and eventual death if untreated 

It is important to note that grass tetany can progress rapidly, often leading to sudden death without obvious warning signs. Regular observation of cattle is essential, particularly during high-risk periods.  

Causes of Grass Tetany

Grass tetany is primarily caused by a deficiency of magnesium in the bloodstream. Several correlated factors contribute to this deficiency: 

Nutritional Imbalance 

Lush pastures, particularly in early spring, are often low in magnesium and high in potassium and nitrogen. These conditions inhibit magnesium absorption in the rumen. Rapidly growing grasses, like ryegrass, wheat or fescue, might have magnesium concentrations insufficient to meet cattle's requirements. 

Soil & Plant Interactions 

Soils high in potassium or nitrogen can lead to forage with a low magnesium content. Acidic or sandy soils often intensify magnesium deficiencies in plants.  

Environmental Factors 

Cool, wet weather conditions promote rapid pasture growth and dilute magnesium concentrations in forages. Frost events can further reduce magnesium availability in plants. 

Animal-specific Factors 

Grass tetany is more common in stocker cattle or replacement heifers that are experiencing rapid weight gain. Older cows, especially those lactating heavily, are more susceptible because lactation increases magnesium demand. 

Diagnosing Grass Tetany

Diagnosing grass tetany in stocker calves involves a combination of clinical observation and laboratory tests. 

Clinical Observation 

Sudden death in seemingly healthy animals grazing lush pastures may indicate grass tetany. Neurological symptoms like twitching and convulsions provide further evidence. 

Laboratory Analysis 

Collecting blood samples can help diagnose grass tetany. Low magnesium concentration in the blood (<1.5 mg/dL) confirms tetany. An autopsy with very low magnesium levels in cerebrospinal fluid can provide conclusive evidence that grass tetany caused death. 

Risk Factors 

Several factors increase the likelihood of grass tetany in stocker cattle: 

1. Seasonality 

Early spring is the most common time for outbreaks due to the growth of lush, magnesium-deficient pastures. Fall regrowth of pastures can also pose a risk. 

2. Dietary Factors

High-potassium forages, such as heavily fertilized pastures, reduce magnesium absorption. Low levels of dietary calcium can intensify magnesium deficiencies. Remember that acidic or sandy soils often intensify magnesium deficiencies in plants. 

3. Animal Characteristics 

Stress from transportation, inclement weather or disease, all common in stocker cattle, can trigger symptoms in susceptible animals. Additionally, lactating cows and older cattle are at higher risk due to increased magnesium demands. 

Economic Impact 

Grass tetany poses significant economic challenges for cattle producers, directly and indirectly.  

Direct Losses 

• Death of impacted cattle results in immediate financial losses. Especially with the current cattle market, losing just one calf can impact your bottom line signifcantly.  
• Veterinary expenses and the cost of treatment add to the economic burden.  

Indirect Losses 

• Reduced performance and productivity, including lower weight gains and milk production. 
• Increased labor and management efforts to monitor and manage the herd. 

Producers can minimize these economic impacts and improve herd health by implementing effective prevention and management strategies. 

Prevention Strategies 

Preventing grass tetany requires a proactive approach to managing cattle nutrition and pasture conditions. The Gain Smart team always recommends prevention when possible. The following strategies can significantly reduce the risk of grass tetany in stocker cattle and all cattle. 

Supplemental Feeding to Prevent Grass Tetany

• Provide free-choice mineral supplements containing magnesium oxide. Cattle typically require 10-15 grams of magnesium per day. 
• Feed high-magnesium concentrates or hay to increase the dry matter (DM) during high-risk periods to ensure adequate intake. 
• Feed Gain Smart mineral powered by AO-Biotics® Amaferm®. Amaferm is a research-proven prebiotic that enhances digestibility and also increases absorption. That absorption factor can help cattle better absorb all the nutrients in the added hay you feed, especially if they eat the mineral correctly. That’s according to Chris Cassady, Ph.D., Beef Cattle Technical Sales Director for BioZyme. 

“Lush forages are low in DM, so Amaferm needs to extract everything it can from the low DM content to help generate more energy. Then, it can use the soluble protein in lush grass more effectively to produce more microbial protein,” Cassady said. 

Pasture Management 

• Avoid over-fertilizing pastures with potassium or nitrogen, as these reduce magnesium availability. 
• Incorporate legumes such as clover or alfalfa into pastures to improve magnesium content. 
• Rotate cattle to less lush pastures during high-risk seasons. 

Supplemental Magnesium Delivery 

• Use magnesium-containing licks, blocks or tubs to encourage consistent consumption. 
• Add magnesium salts to drinking water where feasible. 

Monitoring & Observation 

• Regularly observe cattle for early symptoms of grass tetany, especially during spring grazing. 
• Conduct periodic forage testing to monitor magnesium levels in pastures. 

Treatment of Grass Tetany 

Although prevention is the best step, it doesn’t always work. And grass tetany progresses fast. That’s why prompt treatment is essential to save impacted cattle. The following 4 steps outline an effective treatment protocol: 

1. Immediate Action

Isolate the affected animal from the herd to prevent injury during handling. Minimize stress and avoid overstimulation, which can trigger convulsions, potentially causing more injury. 

2. Administer Magnesium  

Administer intravenous magnesium sulfate under veterinary supervision. For less severe cases, subcutaneous or oral magnesium supplements could be sufficient. 

3. Supportive Care 

Monitor the animal closely for several days to ensure recovery. Provide access to high-magnesium feeds or supplements after treatment to prevent relapse. 

4. Veterinary Assistance 

At BioZyme, we always recommend establishing a veterinarian-client relationship. Consult a veterinarian immediately if symptoms do not improve with initial treatment. A postmortem examination of deceased animals can confirm the diagnosis and help determine preventative measures for the remaining herd. 

What is Gain Smart?  

Gain Smart is a line of vitamin and mineral supplements for stocker cattle that promotes healthy, economical pounds. Gain Smart offers 4 different free-choice vitamin and mineral supplement formulas to fit any feeding scenario.   

The 4 Gain Smart formulas for stocker cattle include:     

• Gain Smart Stocker, which helps cattle maximize efficient gain.    
• Gain Smart Stocker Wheat,  which helps cattle maximize efficient gain on wheat or small grain pasture.    
• Gain Smart Stocker HEAT®, maximizes efficient gain when temperatures are above 70 degrees Fahrenheit. Contains HEAT technology, a combination of essential oils and garlic, to support animals when heat and insects are a challenge.    
• Gain Smart Stocker Balancer RU1600, maximizes efficient gain and balance high-grain diets when mixing TMR rations. Includes rumensin for improved feed efficiency.    

Cassady said that the 2% magnesium in the Gain Smart formulas should be adequate to bring up the magnesium levels for growing stocker calves. 

“A growing calf only needs about 0.10% magnesium in the diet. If an 800-pound steer consumes Gain Smart they’ll add .02 to .05% magnesium to their total diet DM. While it’s not what a 10% mag would do, it definitely helps and still is palatable,” he said. 

The Gain Smart Difference 

All formulas offer the following key benefits:    

• Powered AO-Biotics Amaferm, a prebiotic research-proven to enhance digestibility.    
• Include organic copper, iodine, and zinc for maximum bioavailability and hoof health.    
• Provide nutritional support for a healthy immune system.    

Results Backed by Research   

Amaferm, the key ingredient in most of our BioZyme products, is research-proven to increase digestibility. As a prebiotic, it stimulates the growth of beneficial gut microbes, increasing the overall health of stocker cattle. Research shows that it increases average daily gains by one-quarter (.25) pound per day. Additionally, it improves the absorption of nutrients, so it should help cattle more readily absorb the magnesium that is available to them. 

According to Cassady, with proper management and care, you can prevent grass tetany.  

“Most producers think of tetany as a magnesium deficiency because feed companies use magnesium to prevent occurrence, but really it is excessive intake of potassium. Potassium and magnesium compete for the same absorption pathway,” Cassady said.   

“Think of the absorption pathway like a funnel. Three potassium marbles are trying to get through the funnel at the same time as one magnesium marble. Since the percentage of potassium marbles is greater, that nutrient is more likely to go down the funnel and get absorbed before the magnesium does.”    

Wouldn’t you like to keep your cattle healthy and increase your calf weight gain per day by one-quarter of a pound just by providing a mineral with Amaferm?  

Increase your Calf Weight Gain, Prevent Grass Tetany, the Smart Way!    

Have we convinced you that Gain Smart powered by Amaferm is the best choice for spring stocker grazing? We hope so! Now that you know about Gain Smart, you can get your calves gaining today.    

Gain Smart is available at any one of our local authorized BioZyme Dealers. Locate the dealer nearest you.     

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