What Grasses Cause Grass Tetany? A Deep Dive
What grasses cause grass tetany? Rapidly growing, lush spring grasses, particularly cool-season grasses like ryegrass, fescue, and bluegrass, are most frequently implicated in grass tetany, due to their low magnesium, calcium, and high potassium and nitrogen content.
Understanding Grass Tetany
Grass tetany, also known as hypomagnesemia, grass staggers, or wheat pasture poisoning, is a metabolic disorder primarily affecting ruminant livestock, such as cattle, sheep, and goats. It occurs when the animals’ blood magnesium (Mg) levels become critically low. Magnesium is essential for nerve and muscle function, and a deficiency can lead to severe symptoms, including muscle tremors, incoordination, convulsions, and even death. The condition is most prevalent in lactating animals grazing on rapidly growing pastures, especially in early spring when conditions favor the uptake of potassium and nitrogen by the grasses, antagonizing magnesium uptake.
The Key Culprits: Grass Species and Their Composition
What grasses cause grass tetany? While any rapidly growing grass can potentially contribute, certain species are more consistently associated with the condition due to their inherent nutrient profiles during periods of rapid growth. The risk isn’t solely dependent on the grass species itself, but also heavily influenced by soil conditions, fertilization practices, and the stage of plant maturity.
-
Cool-Season Grasses: These grasses are most frequently implicated because they exhibit rapid growth in the spring, coinciding with peak lactation in many livestock.
- Ryegrass (Lolium spp.): Particularly perennial ryegrass and annual ryegrass varieties.
- Fescue (Festuca spp.): Especially tall fescue.
- Bluegrass (Poa spp.): Kentucky bluegrass is a common example.
- Orchardgrass (Dactylis glomerata): Can contribute, though less frequently than ryegrass or fescue.
- Wheatgrass (Thinopyrum spp.): Can pose a risk, especially when grazed early in the season.
-
Warm-Season Grasses: While less common, certain warm-season grasses can pose a risk, especially if fertilized heavily with nitrogen. These grasses become more of a concern in late summer or early fall after rainfall following a dry period stimulates rapid growth.
- Bermudagrass (Cynodon dactylon): When heavily fertilized.
The problem isn’t necessarily the presence of these grasses per se, but rather their nutrient composition under specific growing conditions. These conditions generally include:
- Rapid Growth: Fueled by abundant moisture and fertility, leading to rapid uptake of nutrients.
- High Potassium (K): Potassium interferes with magnesium absorption in the animal’s digestive tract.
- High Nitrogen (N): Nitrogen promotes rapid growth and can lead to an imbalance of other nutrients.
- Low Magnesium (Mg): Soil magnesium levels may be inherently low, or magnesium uptake by the plants is inhibited by high potassium levels.
- Low Calcium (Ca): Similar to magnesium, calcium is important for nerve and muscle function.
Factors Contributing to Increased Risk
Several factors besides the grass species itself contribute significantly to the risk of grass tetany:
- Soil Fertility: Low magnesium, calcium, and high potassium levels in the soil are primary drivers.
- Fertilization Practices: Excessive nitrogen and potassium fertilization without adequate magnesium supplementation exacerbate the problem.
- Plant Maturity: Young, rapidly growing grasses are typically higher in potassium and nitrogen and lower in magnesium than more mature grasses.
- Weather Conditions: Cool, cloudy weather promotes rapid grass growth and can limit magnesium uptake by plants.
- Animal Physiology: Lactating animals have a higher magnesium requirement due to the loss of magnesium in milk. Older animals may also be more susceptible due to reduced magnesium absorption efficiency.
- Previous History: Farms with a history of grass tetany are likely to experience it again unless management practices are adjusted.
Prevention and Management Strategies
Preventing grass tetany requires a multifaceted approach that addresses both the nutritional needs of the animals and the management of the pasture.
- Soil Testing and Amendment: Regularly test soil to determine nutrient levels and amend with magnesium and calcium as needed. Dolomitic limestone is a common amendment that supplies both calcium and magnesium.
- Magnesium Supplementation: Provide livestock with free-choice mineral supplements containing a high concentration of magnesium oxide (MgO). Magnesium oxide is relatively unpalatable, so mixing it with salt and other minerals can improve consumption.
- Avoid Excessive Nitrogen and Potassium Fertilization: Apply nitrogen and potassium fertilizers based on soil test recommendations and avoid over-application.
- Delay Grazing of Rapidly Growing Pastures: Allow grasses to mature slightly before grazing, as mature grasses tend to have a more balanced nutrient profile.
- Mix Legumes with Grasses: Legumes, such as alfalfa and clover, are generally higher in magnesium and calcium than grasses. Including legumes in pastures can help to balance the mineral content.
- Provide Alternative Forage Sources: Supplement grazing animals with hay or silage, particularly if the pasture is suspected to be high in potassium and low in magnesium.
- Monitor Animals Closely: Observe animals for early signs of grass tetany, such as muscle tremors, incoordination, and excitability. Prompt treatment with intravenous magnesium sulfate can be life-saving.
- Strategic Grazing: Rotate pastures to prevent overgrazing and allow grasses to recover and mature.
Comparing Grass Tetany Risk Levels
The following table summarizes the relative risk levels associated with different grasses, assuming similar growing conditions and fertilization practices:
| Grass Species | Relative Risk of Grass Tetany |
|---|---|
| ——————– | —————————– |
| Ryegrass | High |
| Fescue | High |
| Bluegrass | Moderate to High |
| Orchardgrass | Moderate |
| Wheatgrass | Moderate |
| Bermudagrass | Low (unless heavily fertilized) |
| Legumes (Alfalfa, Clover) | Very Low |
Frequently Asked Questions (FAQs)
What is the best way to supplement magnesium to prevent grass tetany?
Magnesium supplementation is crucial for prevention. Providing free-choice mineral mixes containing at least 12-14% magnesium in the form of magnesium oxide (MgO) is a common practice. Ensure adequate consumption by mixing it with palatable ingredients like salt or molasses. Strategic placement of mineral feeders near water sources can also improve intake.
Are some breeds of livestock more susceptible to grass tetany than others?
While all ruminants are susceptible, older cows and those in early lactation are generally at higher risk due to their increased magnesium requirements and potentially decreased absorption efficiency. Breed differences are less well-defined, but individual animal variations in metabolism can play a role.
How quickly can grass tetany develop in livestock?
Grass tetany can develop very rapidly, sometimes within a matter of hours. Lush, rapidly growing pastures can trigger a sudden drop in blood magnesium levels, leading to acute symptoms. This rapid onset underscores the importance of preventative measures and close monitoring of animals.
Can soil testing accurately predict the risk of grass tetany?
Soil testing provides valuable information about nutrient levels in the soil, including magnesium, potassium, and calcium. However, it’s not a perfect predictor of grass tetany risk. Plant tissue testing can offer a more direct assessment of nutrient uptake by the grasses themselves.
Does liming the soil always prevent grass tetany?
Liming with dolomitic limestone can help to raise soil pH and increase magnesium and calcium availability. However, it’s not a guaranteed solution. The effectiveness of liming depends on the soil type, the existing pH level, and the type of lime used. A balanced approach to soil fertility management is essential.
Is grass tetany only a spring problem?
While most common in the spring, grass tetany can occur any time of year when conditions favor rapid grass growth and nutrient imbalances. Late summer or early fall outbreaks are possible after rainfall following a dry period. Careful monitoring is crucial regardless of the season.
What are the early signs of grass tetany in livestock?
Early signs of grass tetany can be subtle but include muscle tremors, twitching (especially around the face and ears), stiffness, and a lack of coordination. Animals may appear anxious or agitated. These signs should prompt immediate veterinary attention.
Can grass tetany be treated effectively?
Yes, grass tetany can be treated effectively with intravenous administration of magnesium sulfate. However, treatment needs to be administered promptly to prevent irreversible damage or death. Consult with a veterinarian for appropriate diagnosis and treatment protocols.
How does potassium affect magnesium absorption in livestock?
High levels of potassium in the diet interfere with magnesium absorption in the animal’s digestive tract. Potassium competes with magnesium for absorption sites, reducing the amount of magnesium that enters the bloodstream.
What role do legumes play in preventing grass tetany?
Legumes, such as alfalfa and clover, are generally higher in magnesium and calcium than grasses. Including legumes in pastures helps to balance the mineral content and reduces the risk of nutrient imbalances.
Can overgrazing increase the risk of grass tetany?
While not a direct cause, overgrazing can stress plants and alter their nutrient composition. Overgrazed pastures may have reduced root systems and increased susceptibility to nutrient deficiencies. Sustainable grazing management practices are essential for maintaining healthy pastures.
What other conditions can be mistaken for grass tetany?
Several other conditions can mimic grass tetany symptoms, including milk fever (parturient paresis), tetanus, and some types of poisoning. Accurate diagnosis by a veterinarian is crucial for appropriate treatment.