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Grass tetany prevention started last fall

Alan Newport Young cow and calf on short green grass
A basic secret to preventing grass tetany is in grazing management before spring.
Seems everyone has a purchased grass tetany solution, but is there a better way?

Every spring as the grass greens up cattle producers get excited about turning the cows out to grass. If seeing a herd of cows and calves on fresh green grass does not make your heart sing, you probably should get that heart checked out for a defect.

However, along with green-up, talk of grass tetany begins to circulate around the morning coffee table at co-ops and cafes across many parts of America. The talk typically bounces from remedies of high-magnesium lick tubs or loose mineral to adding extra salt. Like any good coffee-drinking discussion, everyone knows someone who did something that nobody else did that worked “the best.”

But one aspect of grass tetany almost always gets left out of this conversation—did we set up our cattle for this problem through poor pasture management?

Fall grazing matters

The biggest fault for us as cattle producers (myself included) is we are cow-centric. Our brains revolve around the animals we love and our focus stays on them, above ground level. But as a wise Nebraska Sandhills rancher once told me, we need to consider ourselves to be “grass farmers” if we want the best for our cows.

Grass tetany is a prime example. Although this is little-discussed over coffee, grass tetany is more likely to occur in pastures with very short grazing heights the previous fall, which have little to no carryover forage residue. Look up a look at an article from North Dakota State University extension in 2014 on the topic if you want to learn more.

The reason these pastures cause the most problems has to do with the mineral composition of short, rapidly growing grass as compared to mature plants. These shorter plants, in particular the cool-season grasses or cereal-grain grasses, are not only low in magnesium, but high in potassium. Since potassium inhibits magnesium absorption through the rumen wall, this double whammy makes short grasses more problematic. Because this balance is better in mature grass, if our pastures had some mature residue left on them from the fall, our cows would get a mix of old and new grass to buffer against tetany issues.

Think back to what this pasture the cows are about to go onto looked like last fall. Did it have a chance for regrowth prior to the winter freeze? Or is this new grass struggling to get its start now in the spring because it was grazed down to nothing last year? If it is struggling today, it is almost certain that grass is pulling even more potassium from the ground into the leaf to grow as quickly as possible. This is good for the grass, but bad for the cow.

Full mineral feeders

Even if you are behind the eight-ball for grazing management, all is not lost to grass tetany. A second key to prevention is maintaining consistent salt and mineral intake. Salt is necessary because it is part of the process to pump magnesium from the rumen into the bloodstream.

There are a lot of variables to consistent intake of free-choice mineral, but one often overlooked factor is cows won’t eat mineral if we don’t have it available to them. Considering our highest risk for grass tetany falls during planting season, how diligent are we at checking our mineral feeders? Checking daily is crucial, because one day without access can trigger grass tetany. Add to this the fact wet spring grass makes cows go through mineral like a teenager goes through pizza, it becomes obvious that our best defense against the disease is keeping the preventative in front of the cows 24-7.

There is a lot of talk around the morning coffee table about things we can’t control. However, with grass tetany we should focus on the things we can control. Start with keeping salt and mineral in front of the cows constantly through the early growing season. Then, work to develop a grazing management plan that leaves residue on the ground in the fall. As the other writers in this issue have elaborated, this will not only combat grass tetany, but lead to benefits for the long-term health of your cattle operation.

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