Is Johnson Grass Safe for Horses? Why Sorghum Hay Is a Risky Shortcut

Is Johnson grass safe for horses? The short answer

Is Johnson grass safe for horses? Not as a regular feed: Johnson grass is a wild sorghum, and horses that eat sorghum-family plants for weeks can develop sorghum cystitis-ataxia, a nerve and bladder syndrome whose damage can be permanent. Stressed plants can also carry prussic acid (cyanide) or high nitrates, so a cheap bale of Johnson grass, Sudan grass or sorghum-sudan hay is a gamble most owners should skip.

That warning got a lot of attention on X this week. On September 20, an equine-therapy ranch posted that people had urged it to save money by feeding Johnson grass hay, and that it refused because the plant can leave horses wobbly and incontinent. The post drew hundreds of likes and dozens of reposts, and other users shared it as a warning to fellow owners.

The timing is no accident. Drought has shrunk hay supplies and pushed prices up in several regions (Virginia declared a hay-shortage emergency on September 16), so cheaper sorghum-family hay can look like a tempting budget option. On September 23, Ohio State University Extension also reminded readers that horses should not graze Johnson grass or other sorghum-type forages.

Why Johnson grass hay is risky for horses

Johnson grass (Sorghum halepense) is a tall, invasive perennial related to grain sorghum (milo), forage sorghum and Sudan grass. It is listed as a noxious weed in 19 U.S. states, is a major weed in Mexico (especially in the north), and thrives in ditches, fence lines and weedy hay fields. Spanish speakers may know it as zacate Johnson or sorgo de Alepo. Cattle producers sometimes use these plants as forage, but horses are a different story.

The risk comes in three forms.

1. Sorghum cystitis-ataxia: the long-term danger

This is the syndrome the ranch was worried about. The Merck Veterinary Manual describes it in horses that eat sorghum species over a long period: hind-end incoordination (ataxia) that can progress to irreversible paralysis, dribbling urine, urine scald and hair loss on the hind legs, and bladder infections that can spread to the kidneys.

• Most documented cases involve weeks of grazing sorghum pastures. Vets first described the syndrome in horses in the late 1960s.
• A 2025 scientific review in the journal Toxicon notes that researchers still don't know exactly how chronic exposure damages the spinal cord.
• That means no one has set a safe amount of sorghum-family forage for horses, and once nerve damage appears, recovery is uncertain.
• Sorghum has also been linked to abortions and birth defects, mostly in cattle and sheep.

2. Prussic acid (cyanide): fast and often fatal

Sorghum plants store a compound called dhurrin that releases cyanide when leaves are chewed, crushed, frozen or wilted. Levels spike in young plants, in fresh regrowth after a drought-breaking rain and in plants hit by frost. Horses are somewhat less sensitive than cattle, but they are not immune.

Curing usually lowers prussic acid, so many people assume dry hay is safe. But in an August 31, 2026 newsletter, Kansas State University reported that when it measured dhurrin in sorghum hay, the levels stayed stable through 1 to 10 weeks of dry storage. Bottom line: drying alone does not make stressed sorghum hay safe, and only a lab test can tell you.

3. Nitrates: the problem that stays in the bale

Johnson grass and other sorghums pile up nitrate when drought, cool weather or heavy fertilizer stunts their growth, and it concentrates in the lower stalk. Like the cyanide-forming compound, nitrate is not removed by drying. Merck notes that hay can be more hazardous than fresh pasture with the same nitrate level, and horses do turn some nitrate into more toxic nitrite in their hindgut, though less than cattle.

Warning signs to know

Here is how the three problems usually show up. Any of these signs is a reason to call your vet right away.

Acute cyanide poisoning moves so fast that animals are often found dead. If you suspect it, remove the feed, bag a sample and call your vet; do not try home remedies. For a refresher on normal vital signs, see our health basics guide.

How to check hay for Johnson grass, Sudan grass and sorghum

You don't need to be a botanist to spot most sorghum-family hay. Open a flake in good light and look for these clues:

• Wide leaves with a white stripe. Johnson grass blades are often about ½ to 1½ inches wide, with a pale midrib running down the center. Timothy and orchardgrass leaves are usually narrower.
• Thick, cane-like stems. Sorghum stems are round, smooth and stout, more like skinny cornstalks than grass stems.
• Big, open seed heads. Johnson grass forms loose, branching seed heads, usually about 4 to 24 inches long.
• The name and the price. Sorghum-sudan hay may be sold as "sudan," "cane hay" or "haygrazer," and it is often priced below horse-quality grass hay.

Then ask the seller three questions:

1. What species are in this hay, and was the field weedy?
2. Was the crop drought-stressed, frosted or heavily fertilized before cutting?
3. Do you have a nitrate test? For any sorghum-family hay, is there a prussic acid test too?

If the answers are vague, pass. If you already bought hay you're unsure about, send a sample to a forage lab through your county extension office. Kansas State suggests sampling 10% to 20% of the bales from each cutting and points out that testing costs far less than losing an animal.

Johnson grass in your pasture: why fall is riskiest

Hay isn't the only route. Johnson grass loves fence lines, ditches and creek banks, and horses will nibble it. Fall stacks the odds: a drought-breaking rain sparks tender regrowth, and the first frost ruptures plant cells and releases cyanide.

• Walk your fences and fence off or remove Johnson grass patches your horses can reach.
• Take extra care after frost, drought, a heavy rain following dry weather, or mowing, since new shoots are the most toxic.
• Don't turn hungry horses out onto weedy ground; feed hay first.
• Ask your extension office about control. Ohio State notes that Johnson grass doesn't tolerate repeated close mowing, which weakens its roots over time.

Safer ways to stretch your forage in a drought

Saving money on hay is smart. Saving it with a sorghum bale isn't. Here is what works better:

• Buy horse-quality grass or legume hay such as timothy, orchardgrass, brome, bermudagrass, teff or an alfalfa mix. Paying a little more per bale beats a vet bill.
• Hay cubes or pellets can replace hay pound for pound, according to University of Georgia Extension. Weigh them, because density varies by product.
• Soaked beet pulp, UGA adds, can cover up to half of the forage portion of the diet.
• A true complete feed can replace all forage for horses that need it, split into several small meals.
• Switch gradually over 10 to 14 days, and keep some long-stem hay in the diet if your horse's teeth allow.
• Cut waste with slow-feed nets and covered storage, and feed by weight. Our nutrition guide explains how much forage a horse needs each day.

What to watch next

• The first frost. Across the southern U.S. and northern Mexico, the first killing frost of fall is the classic trigger for prussic acid in Johnson grass and sorghum. Keep horses away from sorghum-family plants for the season.
• Regrowth after rain. Kansas State warns that nitrate can stay high for at least two weeks after drought-stressed plants start growing again, and that cool weather below about 55°F favors nitrate buildup.
• Hay deals that sound too cheap. As winter hay gets scarcer, more sorghum-sudan and weedy bales may show up for sale. Ask what's in them before you load the trailer.
• Your horse's hind end and bladder. If your horse has eaten sorghum-family forage recently, watch for stumbling behind, dribbling urine or scalded hind legs, and tell your vet exactly what it has been eating.

The ranch that started this conversation had it right: when hay money is tight, the cheapest bale is the one that doesn't put your horse at risk. Keep sorghum out of the manger, test anything you're unsure about, and lean on your vet and extension office for the rest.