Fall Grazing: Protecting Your Herd When the Weather Shifts

By Jeff Mattocks

Fall is just around the corner, and ruminant farmers everywhere are looking for ways to stretch the grazing season. That’s the goal, right? Unfortunately, every year during the spring and fall flush of grass, we hear the same calls: “My cows are bloating” or “We’ve got a case of grass tetany.”

So why are these lush grasses so risky in the cooler seasons? It comes down to weather. Shorter days, cooler temperatures, and better ground moisture all affect how grasses process nutrients. At night, plants pull up moisture and nitrogen from the soil and air, but without enough heat and sunlight, they can’t fully convert those nutrients into protein, fiber, and carbohydrates. Until the sun gets high enough, the grass remains less digestible—and potentially dangerous.

Here’s what happens: the rumen microbes keep breaking down forage, releasing gas and nitrogen, but the cow can’t digest it fast enough. That gas builds up, leading to bloat—and unless you act quickly, it can be fatal. In fact, you may only have one to two hours to intervene.

If you must turn cows out early in the morning, be proactive. Feeding extra magnesium can go a long way in preventing illness. Better yet, wait until later in the morning or around lunchtime, when grass has had time to start photosynthesizing again.

And let’s talk economics. Losing a cow is costly—most dairy or beef cows are worth $1,500–$3,000. Compare that to the cost of prevention: just 2 ounces of Epsom salt (magnesium sulfate) per cow per day, which works out to about 10–12 cents. For a 50-head herd, that’s $5–$6 per day, or $300–$360 for the fall season. A small investment compared to the loss of even a single cow.

If force-feeding magnesium sulfate isn’t practical, you can add it to your free-choice mineral mix. Fertrell also offers Grazier’s Choice with added magnesium, designed to make supplementation easier and more reliable. However, you do it, make a plan now to ensure your herd gets the protection it needs.

Your cows—and your bottom line—are worth it.

If you have questions, our livestock team is always here to help you find the best way to get magnesium into your herd.