By Andi Anderson
With spring’s arrival and pastures starting to green up, producers may feel tempted to fertilize. But experts warn against applying nitrogen or potassium-based fertilizers too early after a drought, as this can raise the risk of grass tetany in livestock.
Grass tetany is caused by low magnesium levels in the blood. Cool-season grasses are naturally low in magnesium, and when fertilized, they can become rich in potassium, which blocks magnesium absorption in ruminants such as cows, sheep, and goats.
Ruminants aren’t efficient at absorbing magnesium through digestion. Magnesium uptake in the rumen is disrupted when potassium levels are high and sodium levels are unbalanced. Magnesium, unlike calcium, can’t be pulled from bones to maintain blood levels, making daily intake essential.
To prevent grass tetany, provide high-magnesium mineral supplements before spring turnout. Cows need 20 grams of magnesium daily, which can be met by consuming 3–4 ounces of a mineral mix with 12–15% magnesium. Simply offering the mix isn’t enough—producers must ensure all animals are consuming it properly.
If the free-choice supplement isn’t being consumed, mix magnesium with palatable feeds like dried molasses or soybean meal. Commercial and homemade mineral mixes are both available.
Experts suggest introducing high-magnesium supplements 2 weeks to 30 days before grazing begins. Though year-round feeding isn’t required, it won’t harm livestock if given early or later into the season.
Older, lactating females are most at risk, while calves, steers, and dry cows are less affected but not immune. Symptoms include nervousness, muscle spasms, loss of appetite, convulsions, and even death. Immediate veterinary help is critical if symptoms appear.
When selecting supplements, check mineral types—organic minerals are better absorbed, though costlier. Magnesium oxide remains effective despite being inorganic.
Careful pasture management and proactive mineral supplementation can prevent losses and ensure a healthy grazing season.
Photo Credit: gettyimages-zoran-zeremski
Categories: Ohio, Sustainable Agriculture