When people think about tetany they think of something that happens only during the spring. It’s something that usually occurs when cattle are eating lush, spring grass, or annual cereal forages. However, it can also occur when cattle are being fed harvested forages like silage or hay.
Grass tetany is most often paired with cattle grazing immature cool-season grasses or lush annual forages. The thing about it is tetany can also happen during the winter when cattle are being fed hay. This can happen with regular hay, alfalfa hay, or annual forages that have been harvested for hay. It is especially true if the hay is being fed in a dry lot and it is the only source of feed.
For those of you not in the know, you may be asking “What is grass tetany?”, “What kinds of problems can it cause my operation?“, and “How do I treat or even prevent it from happening?“. Well in regard to those questions here are some things that you should consider.
What causes grass tetany?
Grass tetany is a metabolic disorder that is caused by a low concentration of the mineral Magnesium in the blood, It can be found in all classes of cattle and if it is not treated in time it can be fatal. Magnesium is a critical mineral to the nervous system and muscle function.
Grass, alfalfa, and cereal grains harvested for hay can be low in magnesium. A hay is considered low if the mineral analysis shows less than 0.15% magnesium in the hay. When it is low in magnesium and calcium, less than 0.4%, along with being high in potassium, greater than 2.5%, tetany is more likely to occur. This can be a problem during dry years like we have experienced this year.
Forages that are likely to cause grass tetany are typically borderline low in magnesium while having high levels of potassium. Also, those forages will also tend to be low in sodium. Potassium levels that are high will interfere with the absorption of magnesium. It is the excess potassium that causes tetany. An imbalance of potassium, calcium, and phosphorus in feed can negatively affect the absorption of magnesium from digestion to the bloodstream. This can magnify your problems.
The stage of production can also play a factor in the risk of getting grass tetany or not. Cows in the late gestation and lactation stages can get it because their body is using the Magnesium they consume for milk production.
Older cows tend to be more likely to get it than their young counterparts. This is because the older ones are not able to pull Magnesium from places like their bones in order to meet their body’s demand for it.
Symptoms
Diagnosing the symptoms of grass tetany just visually can be a little tricky. This is because the symptoms can come on so fast that by the time you can see them the cow could already be dead.
Some of the symptoms can be things like grazing away from the herd, increased irritability, muscle twitching, convulsions, decreased milk production, and even a staggering walk. Unless you are watching your herd very closely it can be difficult to see the early signs of grass tetany.
If left untreated cows will then lie down and begin a paddling-like motion with their legs. The final stages of the symptoms are that the cow will lie down, slip into a coma, and then die.
Ways to treat it
Being able to treat grass tetany in a fast manner can be difficult because the death of the cow can occur rather quickly. One day the cow may look fine but then the next she will be dead.
You will need to restore magnesium levels in the blood of your herd if it has grass tetany. Preventing it from worsening requires immediate action. There are a few different ways that you can go about doing that.
Veterinary professionals can inject the cow with Magnesium and Calcium solutions intravenously. This can work during the early stages of the disease when time is not as critical as later on.
If it is a serious problem and you need to act rather quickly the producer can inject the Magnesium/Calcium solution under the skin.
There are also some oral options that are available to the producer. Though these options are generally to prevent any of your cows from relapsing. These oral sources of Magnesium are:
- A Magnesium oxide powder for putting onto either feed or on the pasture
- Magnesium lick blocks
- Slow-release capsules
- Magnesium sulfate or soluble magnesium chloride that can be added to hay or silage
- Adding magnesium to concentrates
You can purchase these products at your local feed store or from your veterinarian.
Ways to prevent grass tetany
Since it is difficult to treat, or even properly diagnose, tetany prevention is more important. This process begins with testing your hay. Testing will tell you if there are any imbalances in magnesium, potassium, and calcium. I go over how to test your hay in a previous post “Hay sampling: what to know”.
If the hay tests low in magnesium, less than 0.15%, and calcium, less than 0,4%, while also being high in potassium, more than 2.5%, consider using a supplement. You should use a high calcium, high magnesium supplement that contains 10-13% Mg for a 4oz target intake that also has salt.
If you go with that option keep in mind that magnesium oxide has a bitter taste to it. To make it more palatable you can mix it. Use either dried distiller’s grains or soybean meal at 1lb to 50 lbs of the mineral salt mix. This will help to increase intake if your consumption is not at ideal levels. If you are hand-feeding protein or energy you can deliver the magnesium supplement with it.
Another thing to think about when having hay that is high in potassium and low in magnesium is mixing it with other hay. Much like with dealing with ones high in nitrates you can “water down” the problem hay by mixing it with hay that is higher in magnesium and calcium. Alfalfa can be high in potassium also so be sure to test it prior to feeding.
If you are looking for other ways to treat tetany then check out some articles by the University of Nebraska at Lincoln.
