Spring grasses and grass tetany risk: The role of magnesium

Mar 17, 2020

Producers will often say some of their best-milking cows are the ones that go down with grass tetany. Mark Robbins explains why magnesium is so important for spring calving herds on lush grasses and what can be done to prevent grass tetany this spring.


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Tom:      I’m Tom Martin here with Mark Robbins. He is Director of Research and Nutrition Services with CRYSTALYX® Brand Supplements. He joins us from Whitewood, South Dakota. And, we’re talking today about the changing seasons and some of the nutritional risks that are associated with spring grasses.

               Welcome, Mark.

Mark:    Thank you, Tom.

Tom:      So, Mark, spring has arrived or is right around the corner for many cow-calf producers, and with the green grass comes the risk of grass tetany. First of all, what is grass tetany?

Mark:    Sure. So, like you said in the springtime this is a little more prevalent and what you really have are cool-season grasses growing fast and sometimes they’re either a little low in available magnesium or there are other things that are tying up the magnesium.

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               And, grass tetany is a condition in the cow where she has low blood magnesium. Now, magnesium is required by the nerves to relax the muscles, and if you don’t have enough magnesium, you basically get a contraction that doesn’t quit. So, if that happens, you know, heart muscles and your leg muscles can’t function anymore and cows will actually die from that.

               So, when we talk about the seasons changing, this is a season where that can typically happen.

Tom:      So, what makes spring the prime season for this grass tetany condition?

Mark:    So, in the springtime you’ve got a couple of things that can come together that promote grass tetany in cows. So, you’ve got generally wetter weather; you know, a lot of places get the majority of their rainfall or moisture in the spring, and you can also have cool temperatures. And, those two together with the cool-season grasses can create this condition where the grass is low in available magnesium; that, in turn, puts the cow at risk.

               The third thing that kind of enters into this [and impacts] a lot of spring-calving herds and mother cows is, those cows — once they start lactating — their magnesium requirement basically doubles. And then, you have this need for an increased level of magnesium in their diet all of a sudden.

               And, it’s kind of interesting when you talk to customers and producers that have issues with grass tetany, many times they will mention some of their best-milking cows are the ones that go down with grass tetany. And, that’s completely understandable because those higher-milking cows are going to need more magnesium, therefore they’re more susceptible to being short on magnesium.

Tom:      And why is magnesium important, especially [during] this time of year for cows on pasture?

Mark:    Sure. That gets back to that fact that they do start lactating this time of year with your spring-calving herds and that’s when their requirement will double. They’re trying to put more magnesium in the milk for the calf and that’s just why you tend to see it predominantly in the spring.

               Now, you can run into situations in the fall of the year where some pastures have fall regrowth, some lush grass that comes on in the fall, again, cool-season grasses. It’s not out of the question that you could see this actually in the fall as well on some pastures.

Tom:      Are there symptoms or specific signs of grass tetany that producers can watch out for?

Mark:    Sure. So, they sometimes refer to grass tetany as grass staggers, so you’re going to notice cows that are staggering. They may become very aggressive. If they stagger eventually, they’re going to fall down and they’d be laying there sometimes convulsing, sometimes with their muscles just basically twitching and shaking. And, again, that gets back to the lack of magnesium, the inability to relax those muscles.

               The other thing I would say, you know, you can’t necessarily just look at a pasture today or tomorrow or next and go, yeah, this one is going to be a problem. But, what you can do is if you’ve got some history in a pasture or it’s a new pasture you’re going into maybe previous owners or other people who have used it can tell you. Some pastures just seem to have more trouble with grass tetany than others and that’s a lot of time due to the species composition of that pasture.

               So, you can’t always predict it, but you can be ready for it and, like I said, you know, if it’s a warm, dry spring, [there’s] probably less chance of it. If you get a cool, wetter spring, there’s an increased chance of it. So, there are pastures that you may have problems everyone, two [or] three years, something like that and some pastures, you know, you may not have any trouble at all. So, it does vary, but history is probably your best ally there as far as predicting what could happen in the future.

Tom:      Are certain cows more susceptible than others?

Mark:    Yeah, your continental and British breeds are a little more susceptible than your Zebu breeds; the cows with little bit of ear on them, like the Brahman and such. But, you know there’s not a huge difference there, but in general, that’s a true statement.

Tom:      What about prevention, Mark? What can be done to manage it or prevent it?

Mark:    Sure. So, a very common method — just kind of a safety net where you may have a pasture that you typically have a little trouble with this, like I said, you may know this from history — is to feed a supplement that’s high in magnesium. So, you can get minerals that are high-mag minerals; you can get other self-fed supplements. We feed a lot of blocks. We make a lot of blocks with high-magnesium levels and that’s a very good way to do it.

               The blocks we make [are] typically very high in molasses and molasses does a good job of masking unpalatable ingredients. So, some of these ingredients don’t taste very good. Magnesium oxide is very good example of that. Phosphorous is another one that’s very unpalatable. You put that into a CRYSTALYX block with a lot of molasses to help cover it up and you can get decent intake.

               And you need intake every day. This isn’t something that the cow can store. You know the cow to some degree can store Vitamin A; they can store some copper for short periods of time. [They] absolutely can’t store magnesium; they have to hit it every day and that’s another reason that CRYSTALYX works very well. So, it covers up the bad taste and the cows will hit it every day, if not multiple times a day.

               The other thing is, you probably get cows started on a high-magnesium supplement a week or two before the typical time that the grass is going to be lush and growing and maybe susceptible to this. Now, again, I’m not trying to say that your feeding this two weeks ahead to store some magnesium up, but the reason you feed it a couple of weeks ahead of time is to make sure the cows know where the supplement is at [and] they’re used to going to it; you get them started on it.

You get more of the herd actually consuming the supplements, so when the day comes that the grass tetany [and] the low magnesium levels are a risk, the cows are on the supplement and they know where it is every day.

Tom:      So, Mark, are there specific CRYSTALYX products that can help with the risk of grass tetany?

Mark:    Sure. So, like I mentioned, you want a high-mag product. We’ve got a few CRYSTALYX products that we call high-mag. There’s a High-Mag Fescue-lyx®. We’ve got a product called SuperMag™. That’s a 12% protein product that has 4.4% magnesium. And then, other products, we may just have mag in the name; M-A-G. So, there’s a Blueprint® 17 Mag; there is a Breed-Up® 17 Mag

A lot of customers understand that mag stands for magnesium, but [for] anybody that doesn’t, it’s probably good that they understand and recognize those names. High-Mag, SuperMag, or just magnesium in the name generally indicates a product that’s at a higher level of magnesium.

Tom:      Mark Robbins, he is Director of Research and Nutrition Services with CRYSTALYX Brand Supplements.

               Thanks so much, Mark.

Mark:    Thank you, Tom.