Fresh pasture grass might look perfect for horses, but it poses hidden dangers. Grazing provides important nutrients, exercise, and keeps horses mentally engaged.

But grass changes in nutrition throughout the year, so it’s important to keep an eye on how much your horse eats.

Weather and seasonal variations can increase sugar and starch levels in grass, which can be hazardous for horses. Spotting warning signs and picking safe turnout times helps keep them healthy.

This guide explains when grass poses the greatest risk and provides grazing tips for horses prone to EMS. Read on to learn more.​

When is Grass Most Dangerous for Horses? Key Takeaway

Grass is most risky for horses at certain peak times. In the spring, new growth means high levels of sugar and starch. After a frost, stressed plants build up even more sugar. These changes can lead to laminitis, obesity, and other health issues. Horses at risk should have limited turnout during these periods.

Factors Influencing Grass Safety for Horses

Grass safety depends on several factors, including:

Nutritional content

Ryegrass and fescue often have high levels of sugar and starch. Sugar level rises during rapid growth or stress. While horses need sugar for energy, too much causes health problems.

Diets high in sugar but low in fiber raise the risk of laminitis and related disorders. As such, provide fibre-rich grass to support digestion and gut health

Environmental conditions

The weather has a significant impact on the amount of sugar in grass. Sunny days raise sugar levels, and cold nights stop plants from using it, so it builds up by morning. 

Frost, drought, heavy rain, and overgrazing also stress grass and increase its sugar content. Weeds and toxic plants, such as ragwort and buttercup, create additional risks. 

It’s essential to monitor the type of pasture, its growth, and the weather to determine when and how long horses should graze.

​Specific Times When Grass Is Most Dangerous for Horses

Grass sugar levels increase markedly during specific seasons, including:

Spring growth

In spring, grass grows fast and is high in sugar, which can be risky for some horses. This can lead to laminitis, insulin resistance, and weight gain. 

Ponies, miniature horses, and sensitive horses can get laminitis even after a short period of grazing on spring grass.

Late summer and early fall

Late summer grass might look less green, but it can still be risky. The risk is highest during fast spring growth or when grass is stressed in late summer and fall.

Drought and hot days, followed by cool nights, make plants store more sugar.

Grass under stress usually has more sugar than mature grass. Also, when it’s cold, grass stops growing and can’t utilize the sugars produced during the day, so these sugars accumulate in the leaves.

Allowing horses to graze on frosty mornings poses significant health risks. Grass damaged by frost might look safe, but it can still cause laminitis or colic..​

Signs of Grass-Related Illness in Horses

Even well-cared-for horses can develop health problems from pasture exposure. Spotting warning signs early is key to preventing serious issues.

Laminitis

Laminitis is a serious condition associated with grass consumption. It occurs when excess sugar disrupts hoof circulation, causing inflammation of the laminae. 

Key symptoms include limping, reluctance to move, hot hooves, and a strong digital pulse. Affected horses may also shift weight to the heels or lie down more frequently.

Colic

Excessive sugar intake disrupts gut fermentation, resulting in gas accumulation or impaction. Colic symptoms include pawing, rolling, lying down, inappetence, or absence of manure production. 

Abdominal pain following grazing should be addressed promptly, as it may signify metabolic issues..

Metabolic distress

Some horses develop long-term metabolic problems that can be difficult to identify. Insulin resistance, which is common in EMS and Cushing’s disease, gets worse with high sugar. 

Watch for weight gain, tiredness after grazing, and fat deposits like a cresty neck or fat pads near the tail. Changes in behavior, like being grumpy or not wanting to work, can also be signs.

Subtle red flags

Watch for subtle signs, such as uneven hoof rings, a shorter stride, or unusual sweating. If you notice these, it may be linked to pasture. 

Acting early by limiting grazing or providing safer forage can prevent further problems. Contact your veterinarian if you notice any symptoms.

Is Grass Dangerous for My Horse?

Grass isn’t inherently dangerous, but issues arise when susceptible horses graze at risky times. Most healthy, active horses thrive on fresh pasture, but some are more at risk. 

Overweight horses can get obese and strain their hooves from overindulging sugar-rich grass. Ponies and miniature horses, used to eating less, can get sick on modern pastures. 

Horses with past laminitis can have relapses, and those with EMS or Cushing’s disease can’t handle even moderate amounts of grass.

Workload is another important factor. Horses that exercise regularly can burn off extra calories from grass. On the other hand, horses that aren’t active build up sugar and starch faster. 

Age matters too. Young horses can handle richer grass better than older ones with slower metabolisms. 

Additionally, grass composition changes with the seasons, so a pasture that’s safe in summer might be risky in spring or after a frost.

The safest approach is to control how much grass your horse eats, rather than taking them off pasture completely. 

Timed turnout, grazing muzzles, or dry lots can help limit intake. Giving hay before turnout can prevent overgrazing and maintain their gut health. 

With good management, even sensitive horses can enjoy pasture without getting sick. The aim is to let horses graze naturally while avoiding hidden risks.

Types of Grass that Pose a Higher Risk to Horses

Horses are more susceptible to metabolic disorders when grazing on certain grass species.

Ryegrass and Fescue

Ryegrass grows well but stores a lot of sugar, which can be risky for sensitive horses. If ryegrass is infected with endophytes, it can cause ryegrass staggers, a nerve problem in animals. 

Fescue, especially when infected, is dangerous for expectant mares and can cause problems with pregnancy and foaling.

Improved pasture grasses vs. native grasses

Improved pasture grasses, which are bred for cattle, grow fast and store more sugar. The high sugar content is especially detrimental for horses prone to laminitis or metabolic issues. 

Native grasses grow more slowly and have less sugar, making them safer but less productive. Accidentally planting improved grasses can increase the risk of health problems associated with grass.

Weeds and toxic plants

Weeds such as buttercups, ragwort, and horsetail can introduce toxins into pastures. Horses usually avoid them, but might eat them if there’s not enough grass. 

Rotating pastures, reseeding, and mowing can help mitigate the risks associated with sugary grass and toxic weeds. Knowing what plants are in your pasture is important for safe grazing. 

Testing your forage or planting horse-friendly grass mixes can make grazing safer and keep horses healthier.

Horses at Most Risk of Grass Toxicity

Not every horse will have health problems from the pasture, but some are at higher risk. It’s a good idea to work with your veterinarian and farrier to create a plan that meets your horse’s specific needs.

Ponies and easy keepers

These animals are accustomed to eating sparse forage and are very efficient at utilizing their calories. Rich pastures can overload their system, often leading to obesity and laminitis.

EMS horses

Horses with EMS struggle to regulate insulin effectively. Eating grass high in sugar can exacerbate the condition and increase the risk of laminitis.

Horses with Cushing’s disease (PPID)

Older horses with Cushing’s disease (PPID) undergo hormonal changes that impact their metabolism. Even a little sugar can cause laminitis flare-ups in these horses.

Previously foundered horses

Horses with a history of laminitis are very sensitive to high-sugar grass, which can quickly cause painful relapses because their hooves are fragile. 

These horses require careful grazing plans, often involving the use of grazing muzzles or limited pasture time.

Preventive Measures for Horse Owners

Regularly managing grazing is key to keeping horses safe from grass-related problems.

Monitoring grazing conditions

Check your fields regularly to assess the growth of the grass and its condition. Watch the weather, since sunny days followed by cool nights or frost can raise sugar levels. 

Identify the types of grass and weeds you have, and be cautious with excessive ryegrass or toxic plants. For the best results, test your forage to see how much sugar it contains.

Time pasture access carefully

Timing pasture access is critical. Grass sugar peaks in the late afternoon and early evening after sunny days. Early morning is safer for grazing if the previous night was warm. 

Avoid turnout on frosty mornings and limit access during rapid spring growth. Offering hay before turnout helps curb hunger and reduce the likelihood of binge grazing. 

Grazing muzzles slow intake while allowing natural behavior. Dry lots with slow feeders provide safe forage when pastures are too risky. Gradually introduce lush spring grass to prevent sudden metabolic overload.

Seek veterinary and professional support

Regular vet checkups can catch metabolic problems early. Blood tests can detect insulin resistance or Cushing’s disease before they worsen. 

Equine nutritionists can help you pick the right forage and supplements, and make safe feeding plans for sensitive horses.

Benefits of Grazing Horses at Night

Allowing horses to graze at night is a good way to reduce health risks for sensitive horses. During the day, especially when it’s sunny, plants make and store sugars. If nights stay warmer than 40°F, plants use up these sugars, so levels are lower by morning.

Turning horses out from late evening to early morning means they eat when sugar levels are lower. This is especially useful in spring and fall, when sugar is highest during the day. 

Night turnout also keeps horses cooler and less stressed. Horses tend to graze more calmly at night, which benefits the entire herd.

Safety is still important. Ensure fences are secure, there’s enough light, and be cautious of local wildlife. 

Providing hay during the day and grass at night helps maintain steady nutrition. Night grazing lets horses act naturally while staying safe.

FAQs 

Conclusion

Grass itself isn’t dangerous, but the environment can make it risky. Spring and fall grass with high sugar levels can turn pastures into a hazard for horses.

The risk is highest for horses with laminitis, EMS, or Cushing’s disease. Knowing when these high-risk times happen helps you plan turnout more safely.

Timed grazing, letting horses out at night, and using dry lots can help keep them safe and healthy. With careful management, pasture can still be a good feed for horses.