Protecting Your Herd During Fall Grazing

Why Fall Grasses Can Be Risky

Although many producers focus on spring pastures as being high risk, fall grazing carries similar hazards. Cool nights + good moisture + shorter days combine to produce grasses that are lush but less digestible, which can lead to rumen upsets and bloat.

Key Risk Mechanics

As grasses grow in the cooler, wetter fall conditions, they pull up moisture and nitrogen during the n ight but they don’t have as much daylight/heat to convert those into mature fibre, stem or structural carbohydrates. That results in high moisture, high N (protein fraction) but low effective fibre and slower plant metabolism → less digestible forage.

That lower digestibility can slow rumen evacuation, increase gas build-up, and lead to bloat when animals eat too much too fast.

Meanwhile, cool-season grasses, especially regrowth or early fall flushes, often have low magnesium (Mg) levels or antagonistic high potassium (K) or nitrogen ( N ) which interfere with Mg uptake by the animal. This sets the stage for grass tetany.

Then What Happens?

Bloat: Gas builds in the rumen, often from animals turned onto lush legume or high moisture grass pastures when hungry or moist. The timing is critical — right after frost, early morning, or when the grass is wet.

Grass Tetany: Also called “staggers,” this is a metabolic disorder characterized by low blood Mg in ruminants grazing lush, Mg-deficient pastures (and often high K). Symptoms can progress rapidly to convulsions and death.

In non-ruminant animals – such as horses – similar dangers from fall pastures are present, but often show up as colic (digestive upset) or laminitis (inflammation in the hooves).

Practical Prevention Strategies

Here are some actionable steps to reduce the risk:

Delay turnout

Wait until pastures have dried after dew or rain (especially after frost or that first fall flush) before moving them onto the pasture, or to a new section of rotational grazing. Turn animals out later in the day when grasses have had a chance to ‘work’ in the daylight, usually around noon or so.

Fill them up with dry forage first

Give animals dry hay/forage before allowing access to high-risk pasture. This reduces the binge effect and the sudden influx of lush forage.

Pasture and Forage management

Avoid turn out on pure, young, rapidly growing grass flushes — especially cool season grasses or cereal covers. Where possible, include legumes which often have higher Mg and more structural fibre, which mitigate some risks.

Monitor fertilization: high N & K fertilizing increases risk of tetany because K antagonizes Mg in the rumen.

Supplementation of key minerals

For grass tetany: ensure animals have access to a mineral mixture that provides adequate magnesium such as Grazier’s Choice with added magnesium from Fertrell, or a magnesium block. You can also add epsom salt (magnesium sulfate) to your existing free-choice mineral to boost the magnesium content. You want to have a mineral that contains 10-14% magnesium, or about .6 ounces of pure Mg daily per head.

For bloat: consider anti-bloat measures (adding oil to your water trough) and avoid abrupt grazing changes that can upset the balance of the rumen. Make sure your herd has access to adequate salt amounts.

Combine mineral supplementation with the management practices above (delayed turnout, dry hay first, pasture mix, etc.) for best results.

Take-aways:

Fall grasses can pose hidden risks: bloat (from lush, wet, high-moisture/low-fibre pasture) and grass tetany (from Mg-deficient, high-K/N forage).

Prevention = good timing of turnout + ensuring animals are fed/have dry forage first + pasture composition + mineral support.

Using a mineral product like Grazier’s Choice (especially the Mg version) helps ensure animals have the micronutrient support they need.

Always monitor animals closely when first grazing new pasture flushes — the onset of issues can be very rapid.

Happy grazing!