What Your Horse Is Actually Eating — A Guide to Pasture Grasses, Grazing Dangers & What Belongs in the Field
Not all grass is the same, and not all of it is safe. From the fescue in your back pasture to the clippings your neighbor left at the fence line, what your horse grazes on every day has a direct impact on weight, metabolic health, and soundness.
By Notting Hill Equine · The Editorial · Horse Health & Pasture
There is a version of horse keeping in which the pasture is simply the green space outside the barn — something that exists, something the horse enjoys, something that takes care of itself. It is a reasonable assumption if you have never thought about it carefully. It is also a dangerous one.
The pasture is not a neutral backdrop. It is a complex ecosystem of grasses, legumes, weeds, and sometimes toxic plants — all competing for space, all interacting with your horse's digestive system in ways that range from deeply beneficial to acutely dangerous. The same field that sustains a healthy horse through summer can accumulate sugar levels that trigger laminitis in spring. The same fence line that looks tidy can harbor plants that cause liver failure. And the lawn clippings your well-meaning neighbor piled at the gate on a Saturday afternoon can kill a horse by Sunday.
This is not a reason to be afraid of turnout. Horses evolved to graze — it is the foundation of their digestive health, their mental wellbeing, and their physical soundness. But it is a reason to know what is actually growing in your field, and what the consequences are when the wrong things grow there.
17
Hours per day a horse will graze given free access to pasture
700+
Plant species documented as toxic or harmful to horses in North America
#1
Cause of laminitis in horses is diet-related — predominantly spring pasture
The pasture grasses
What Is Growing in Your Field — and Whether It Should Be
Most horse pastures in North America are a mixture of cool-season and warm-season grasses, often with legumes such as clover or alfalfa mixed in. Not all of these are equally suitable for horses, and the same grass can be safe or risky depending on the season, the growth stage, and the individual horse's metabolic health. Here is what you are most likely to find and what it means.
Timothy
Safe · Recommended
The gold standard of horse pasture grasses and the most widely used hay grass in North America for good reason. Timothy is palatable, relatively low in non-structural carbohydrates (NSC) compared to many alternatives, and well-tolerated by the vast majority of horses. It produces a clean, stemmy growth that horses find highly palatable without the sugar spikes associated with lush, rapidly growing grasses. If you are overseeding a worn pasture, timothy belongs in the mix.
Orchard Grass
Safe · High Quality
A high-yielding, palatable cool-season grass that horses tend to prefer over timothy in side-by-side grazing tests. Orchard grass is higher in calories than timothy — an advantage for hard keepers and performance horses, a consideration for easy keepers. It establishes quickly, tolerates partial shade better than most pasture grasses, and remains productive even under heavy grazing pressure. A reliable choice for performance horse operations.
Kentucky Bluegrass
Safe · Moderate NSC
The default lawn and pasture grass across much of the northern United States, and generally safe for horses in managed quantities. Bluegrass is highly palatable, spreads aggressively via rhizomes to fill bare patches, and handles hoof traffic reasonably well. The caution: it is among the higher-NSC cool-season grasses, and in spring when it is growing rapidly and fructan levels peak, metabolically sensitive horses — those with PPID, EMS, or a history of laminitis — should have their access managed carefully.
Bermuda Grass
Safe · Warm-Season
The dominant warm-season pasture grass across the southern United States and increasingly common in show horse operations from Florida to California. Bermuda is lower in NSC than most cool-season grasses — a significant advantage for insulin-dysregulated horses — and highly productive in heat and drought conditions that would devastate a cool-season stand. Coastal Bermuda hay is widely used and well-regarded. Its limitation is that it goes dormant and provides minimal nutrition in cold weather, requiring cool-season overseeding or supplemental hay through winter.
Tall Fescue
Caution · Endophyte Risk
The most widely grown pasture grass in the United States — and one of the most problematic for horses in certain circumstances. The issue is not fescue itself but the endophytic fungus Neotyphodium coenophialum that lives inside the vast majority of established fescue stands. Endophyte-infected fescue produces ergot alkaloids that cause serious reproductive problems in pregnant mares: prolonged gestation, thickened placenta, agalactia (failure to produce milk), and foal loss. Pregnant mares should be removed from endophyte-infected fescue no later than 60–90 days before their due date. Non-pregnant horses tolerate fescue reasonably well, though endophyte infection is still associated with reduced weight gain and heat stress. Endophyte-free or novel-endophyte fescue varieties exist and are the correct choice for any operation with broodmares.
Ryegrass (Perennial)
Caution · Staggers Risk
A highly productive, palatable cool-season grass commonly used in overseeding mixes. In normal conditions, perennial ryegrass is safe and nutritious. The risk arises under stress: during hot, dry summers, perennial ryegrass infected with the endophyte Neotyphodium lolii can produce lolitrem B, a neurotoxin responsible for ryegrass staggers — a condition characterized by muscle tremors, incoordination, and in severe cases, collapse. Ryegrass staggers is rarely fatal but can cause injury. Remove affected horses from infected pasture and symptoms typically resolve within days to weeks.
Sorghum / Sudan Grass
Danger · Do Not Graze
Sorghum, sudangrass, and their hybrids are occasionally grown as summer forage crops and should never be grazed by horses under any circumstances. These grasses produce prussic acid (cyanide) under stress conditions — drought, frost, overgrazing, or rapid regrowth — and can cause acute cyanide poisoning: rapid breathing, muscle tremors, convulsions, and death, sometimes within minutes of ingestion. Extended grazing of these species is also associated with sorghum cystitis ataxia syndrome, a progressive neurological and urinary disorder with no effective treatment. Do not plant these species in any field that horses will access.
Johnson Grass
Danger · Toxic Under Stress
A warm-season perennial weed grass common in disturbed soils and roadsides across the southern and central United States. Like sorghum, Johnson grass produces prussic acid under stress conditions — frosted growth, drought-stressed regrowth, and wilted material are particularly dangerous. It is also associated with nitrate toxicity. Johnson grass is often found along fence lines and in poorly maintained pasture perimeters. Walk your fence lines and remove it wherever it appears.
The clippings problem
Why Lawn Clippings Are One of the Most Dangerous Things at the Fence Line
This is the piece of pasture knowledge that is most urgent and least widely understood — including among people who genuinely love horses and mean no harm. Every spring and summer, well-intentioned neighbors, boarders, and property owners pile fresh lawn clippings at the fence line or toss them into the paddock as a treat. Horses eat them eagerly. And horses die from them regularly.
The danger is not the grass itself in most cases — it is the form in which it is consumed, and the contents it may carry.
Why Clippings Kill — The Mechanism
Fermentation rate. When grass is cut and piled, it begins fermenting almost immediately. A horse that eats a large quantity of rapidly fermenting clippings ingests material that continues to ferment inside the hindgut at an accelerated rate, producing gas and lactic acid faster than the digestive system can manage. The result is colic — sometimes severe enough to require surgery, sometimes fatal.
Chewing is bypassed. Horses grazing in a pasture take small bites, chew thoroughly, and ingest grass slowly over many hours. Clippings presented in a pile are consumed in large boluses with minimal chewing — overwhelming the digestive system with a volume of material it was not designed to process at that rate.
Lawn chemicals. Most residential lawns are treated with herbicides, pesticides, fungicides, or fertilizers — many of which are toxic to horses in sufficient quantities. Clippings from treated lawns concentrate these chemicals in the cut material. The homeowner who applied the lawn treatment two weeks ago and considers the yard "safe" may not realize that dried herbicide residue remains on the clippings they are tossing over the fence.
Toxic plant contamination. Lawn mowers do not discriminate. A bag of clippings from a residential lawn may contain sycamore seedlings, yew, oleander, foxglove, or any number of ornamental plants toxic to horses — all chopped fine and mixed into an otherwise harmless-looking pile of grass.
The rule is absolute and has no exceptions: no lawn clippings, ever, from any source. Post a sign at your fence line if necessary. Have the conversation with your neighbors before spring, not after an emergency. The horse that eats a bucket of clippings on a Saturday afternoon may be colicking by midnight.
No lawn clippings, ever, from any source. The rule has no exceptions.
The spring pasture problem
Why Spring Grass Is the Most Dangerous Time of Year for Many Horses
Spring pasture is lush, green, and highly palatable — and for a significant portion of the horse population, it is a metabolic hazard that must be actively managed. The problem is not the grass per se but its sugar content at this particular moment in the growing cycle.
Cool-season grasses accumulate non-structural carbohydrates — primarily fructans and simple sugars — as a response to the conditions of early spring: bright sunlight driving photosynthesis, cold nights slowing plant growth, and rapid new growth producing high concentrations of sugars that have not yet been metabolized into structural plant material. The result is grass that is simultaneously beautiful and dangerous for horses predisposed to insulin dysregulation, equine metabolic syndrome, or a history of laminitis.
Fructans in particular are not digested in the horse's small intestine — they pass directly to the hindgut where they are fermented rapidly by bacteria, causing shifts in hindgut pH that kill beneficial bacteria, trigger endotoxin release, and initiate the cascade that produces laminitis. A horse that was perfectly sound through the winter can founder on spring grass within a week of unrestricted turnout.
Managing Spring Grazing — Practical Steps
Time turnout for lower-sugar windows. NSC levels in pasture grass are lowest in the early morning hours before photosynthesis has had time to accumulate sugars, and after a period of overnight cloud cover. They are highest on sunny afternoons and after a cold, clear night followed by a warm, sunny day — the classic "founder weather" that every experienced horseperson knows. Limit at-risk horses to early morning turnout and bring them in before midday during peak risk periods.
Use a grazing muzzle. A well-fitted grazing muzzle reduces grass intake by approximately 75–80% while still allowing the horse the mental and physical benefits of turnout. For horses with EMS, PPID, or a laminitis history, a grazing muzzle is not a punitive measure — it is a management tool that allows them to live a normal turnout life without the metabolic consequences of unrestricted access.
Avoid stressed or frost-damaged grass. Grass that has been frosted, drought-stressed, or recently heavily grazed accumulates higher NSC concentrations as a survival mechanism. The day after a late spring frost is one of the highest-risk grazing days of the year. Keep susceptible horses off pasture on these days entirely.
Know which horses are at risk. Any horse with a cresty neck, a history of laminitic episodes, a diagnosis of EMS or PPID, or a body condition score above 6 should be treated as a high-risk grazing candidate and managed accordingly from the first day of spring turnout.
Toxic plants
What Should Never Be in Your Pasture — or Anywhere Near It
Toxic plants in horse pastures fall into two broad categories: those that horses will generally avoid unless nothing else is available, and those that horses will actively seek out and eat in quantities sufficient to cause serious harm. Knowing which plants are in your fields — and which of your neighbors' ornamentals are hanging over the fence — is not optional horse keeping. It is the baseline.
Ragwort (Senecio jacobaea)Liver failure · Cumulative · Often fatal
One of the most dangerous pasture weeds in the world. Ragwort contains pyrrolizidine alkaloids that cause progressive, irreversible liver damage — the insidious element is that symptoms may not appear until the liver is already severely compromised, often months or years after exposure. Horses typically avoid fresh ragwort but will eat dried ragwort willingly — making contaminated hay a serious risk. Inspect hay sources and walk pastures in late summer when ragwort is most visible.
Yew (Taxus species)Cardiac arrest · Extremely rapid · Often fatal
Arguably the most acutely dangerous plant a horse can encounter. All parts of the yew plant — bark, leaves, seeds — contain taxine alkaloids that interfere directly with cardiac muscle function. Death can occur within minutes of ingestion, often before any symptoms are observed. A single mouthful of yew clippings tossed over a fence from a neighbor's garden hedge is sufficient to kill an adult horse. Yew is extremely common in residential landscaping across North America and the UK. Know what is planted along your fence lines and your neighbors'.
Sycamore (Acer pseudoplatanus) — Seeds and SeedlingsAtypical myopathy · Seasonal · Often fatal
Sycamore seeds (helicopters) and seedlings contain hypoglycin A, the toxin responsible for atypical myopathy — a severe muscle disease that destroys skeletal and cardiac muscle tissue. Atypical myopathy is seasonal, occurring primarily in autumn when seeds fall and in spring when seedlings emerge, and has a mortality rate of approximately 75% in affected horses. Paddocks with or adjacent to sycamore trees require careful management: remove fallen seeds and seedlings, and limit turnout during high-risk periods.
Oleander (Nerium oleander)Cardiac · Extremely toxic · All parts
Common in warm-climate landscaping across the southern and western United States, oleander is highly toxic to horses in all its parts — fresh, dried, or clipped. A small quantity of leaves can cause severe cardiac arrhythmia and death. It is frequently planted as a decorative hedge along fence lines precisely where horses can reach it. If oleander is growing anywhere within reach of your horses, it must be removed entirely or fenced off at a distance that allows no access including fallen leaves.
Red Maple (Acer rubrum) — Wilted LeavesHemolytic anemia · Wilted leaves specifically
Fresh red maple leaves are not significantly toxic to horses. Wilted leaves — those that have fallen or been cut and partially dried — are. The wilting process concentrates gallic acid and other oxidants that cause hemolytic anemia in horses by destroying red blood cells. A windstorm that drops wilted maple branches into a paddock, or a branch pruned from a tree and left within reach, is the typical exposure scenario. Remove fallen branches promptly and do not allow trimmings to accumulate in or near horse areas.
Black Walnut (Juglans nigra)Laminitis · Shavings exposure · Roots and hulls
Black walnut toxicity in horses most commonly occurs through exposure to black walnut shavings in bedding rather than through grazing — even a small percentage of black walnut in a shaving mix can trigger severe laminitis within hours. The toxin juglone is present in the roots, bark, hulls, and leaves. Horses pastured near black walnut trees may be exposed through root contact in wet conditions or through fallen hulls. Confirm your bedding source is free of black walnut before it enters your barn.
Hemlock (Conium maculatum)Neurological · Respiratory failure · Fatal
Poison hemlock — the plant responsible for the death of Socrates — grows throughout North America in disturbed soils, roadsides, and fence lines, often reaching considerable height before it is identified. It contains coniine and related piperidine alkaloids that cause progressive neuromuscular blockade: weakness, incoordination, and respiratory paralysis. Horses typically avoid it due to its unpleasant smell but will consume it when other forage is scarce. Walk fence lines and property margins in spring and early summer when hemlock is most visible and remove it before it seeds.
Bracken Fern (Pteridium aquilinum)Thiamine deficiency · Cumulative · Chronic exposure
Bracken fern is common in woodland pastures and shaded areas and contains thiaminase, an enzyme that destroys thiamine (vitamin B1) in the horse's body. Toxicity is cumulative — a horse must consume significant quantities over an extended period before clinical signs appear, which include incoordination, muscle weakness, and in severe cases, a characteristic "bracken staggers" presentation. Horses typically avoid bracken but will graze it when other forage is depleted. Keep pastures well-maintained to reduce competition from bracken, and supplement hay during periods of poor pasture availability.
The pasture audit
Walking Your Field — What to Look for and When to Do It
A pasture audit is not a one-time event. It is a seasonal practice that belongs in every horse owner's calendar: once in early spring when new growth makes previously invisible plants suddenly identifiable, once in late summer when stress conditions push weeds into prominence, and once in autumn when seeds fall and the risk profile of the field changes again.
Walk the entire perimeter of every field your horses access. Look along fence lines specifically — this is where weeds establish most easily because they are less likely to be grazed and more likely to be adjacent to neighboring gardens and ornamentals. Note any plants you do not recognize and photograph them for identification before your horses go back in.
Pay particular attention to what is growing on the other side of every fence your horses can reach through. The neighbor's prize yew hedge, the ornamental oleander along the property line, the sycamore tree overhanging the paddock corner — these are not your plants, but they are absolutely your responsibility to manage. A polite conversation with a neighbor is significantly easier than an emergency call to the veterinarian.
Pasture Audit Checklist — Do This Every Season
Walk every fence line. Look for weeds, toxic plants, and ornamentals that horses can reach through or over the fence.
Check neighbor plantings. Identify any trees or shrubs overhanging or adjacent to your horse areas — yew, oleander, sycamore, and red maple are the highest priority.
Look for ragwort. Check in mid to late summer when it is most visible. Remove the entire root — ragwort regrows vigorously from the crown if only the top is pulled.
Identify your grass species. If you are not certain what is growing in your pasture, take samples to your local agricultural extension office for identification. Many offer this service free or at low cost.
Test for endophytes. If your pasture contains significant tall fescue and you have broodmares, test for endophyte infection. Your extension office or a private lab can analyze samples.
Check for signs of stress. Overgrazed pastures, bare patches, and compacted areas are where weeds establish. A pasture in poor condition is a pasture with a higher proportion of problem plants.
Soil test and overseed as needed. A well-maintained, densely growing pasture with desirable grasses is the single best defense against toxic weed establishment. Competition from healthy grass is more effective than any herbicide program.
"The pasture is not a backdrop. It is the foundation — of digestive health, mental wellbeing, and a soundness that lasts a season and beyond."
— The Editorial, Notting Hill Equine
Notting Hill Equine is a premium English tack and sport horse lifestyle shop for hunters, jumpers, and warmblood riders. Explore the full collection at nottinghillequine.com.
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