TURNOUT OF HORSES ON PASTURE AND THE RISKS OF LAMINITIS
Ing. Lucie Humeni
Pasture represents a natural way for horses to obtain feed. In part of the horse population—especially those with insulin dysregulation, obesity, or a history of laminitis—high intake of non-structural carbohydrates from fresh forage can trigger pathological processes in the hoof laminae. The risk is not the access to grass itself, but rather a sudden increase in the intake of non-structural carbohydrates without sufficient adaptation. Below I summarize what actually occurs in the body and how to manage grazing so that pasture becomes a benefit rather than a risk.
What is laminitis?
Laminitis is an inflammatory and metabolic disease of the hoof laminae, the lamellar apparatus. Inside the hoof there are lamellae (fine structures) that firmly connect the hoof wall to the coffin bone and ensure its stable position within the hoof capsule. If these structures become damaged, the connection is disrupted and the suspensory apparatus of the coffin bone weakens. As a result, in more severe cases the bone may shift or rotate relative to the hoof wall, which significantly affects hoof mechanics and the horse’s movement.
Fructooligosaccharides and non-structural carbohydrates
Grasses store energy in the form of fructans. Fructans are chains of sugars (technically fructooligosaccharides) that horses cannot break down in the small intestine because they lack the necessary enzymes. This means these carbohydrates are not absorbed into the bloodstream in the usual way but instead pass into the large intestine.
There, they undergo rapid fermentation by microorganisms. If the amount of fructans is excessive, fermentation accelerates to the point that intestinal pH decreases, some bacteria die, and substances they release (endotoxins) may pass through the intestinal wall into the bloodstream and trigger inflammatory reactions.
However, the fructan content is not the same in all plants. Grasses—especially fast-growing species such as perennial ryegrass—can accumulate high amounts of fructans, while legumes generally contain fewer fructans but more protein. This means the botanical composition of the pasture significantly affects the risk of laminitis. Horses grazing predominantly grass-based pastures are exposed to higher concentrations of rapidly fermentable carbohydrates than those grazing more diverse pastures containing legumes.
Why are early morning and frosted pastures the riskiest?
The fructan content in grasses fluctuates during the day and is influenced by temperature. During sunny days, plants produce sugars through photosynthesis. If the night is cold (below approximately 5 °C), the plant cannot use these sugars for growth and stores them in its tissues. In the morning, the leaves therefore contain a high concentration of rapidly fermentable carbohydrates, meaning the horse receives a “full dose of sugar” immediately after being turned out.
Frosted grass makes the situation even worse. Low temperatures slow down or stop plant growth, but the sugars produced during the previous day remain inside the leaves. As a result, even a small amount of frosted grass can contain excessive levels of fructans.
Season and level of risk
The content of non-structural carbohydrates is influenced by the stage of vegetation, light intensity, and temperature. The most risky periods are spring (rapid growth and fluctuating temperatures) and autumn (cool nights and sunny days).
A relatively safer period is stable, warm summer weather without large temperature fluctuations, when grass is more mature, contains more fiber, and has a lower proportion of soluble sugars. Young, rapidly growing pasture generally contains higher concentrations of non-structural carbohydrates than older, lignified grasses.
How should horses be introduced to pasture?
Adaptation must always be gradual. The microbiota of the large intestine needs time to adjust.
Recommended procedure for healthy horses:
- start with 15–30 minutes per day
- increase the time by 15–30 minutes every 2–3 days
- reach the target grazing time within 2–3 weeks
For at-risk individuals it is advisable to:
- use grazing muzzles
- limit access to morning pasture
- prefer late afternoon turnout when temperatures are stable
- monitor body condition
Sudden full-day turnout after winter represents a significant predisposing factor for the development of laminitis.
Water and mineral licks
When grazing, we must not forget about water. Adequate water intake supports stable fermentation processes and helps prevent hemoconcentration (thickening of the blood). Very delicate microcirculation occurs in the hoof laminae. If the blood becomes thicker, it flows less easily through small vessels, oxygen supply to the tissues worsens, and the tissues become more susceptible to damage.
Mineral licks are also an important component of pasture management. The mineral composition of pasture forage is not balanced and often does not cover the requirement for sodium or certain trace elements. Mineral licks therefore allow horses to continuously supplement especially sodium, which is essential for hydration regulation, nerve function, and maintaining internal physiological balance.
The importance of hay during grazing
In practice, I often encounter the opinion among stable owners that if a horse has pasture, hay is unnecessary. However, even during periods when pasture is abundant, I do not consider it appropriate for a horse to rely exclusively on fresh forage.
Fresh grass contains a high proportion of water and rapidly fermentable carbohydrates but less structural fiber than hay. The horse’s digestive tract is adapted to the continuous intake of fiber with a higher content of plant cell walls, which stabilizes the fermentation environment in the cecum.
Hay provided alongside pasture slows feed intake, limits the sudden consumption of larger amounts of sugars, and supports a more stable fermentation process. It also prolongs feeding time and contributes to increased saliva production. Therefore, even when grass is plentiful, the combination of pasture and good-quality hay makes more metabolic sense than fresh forage alone—especially for horses prone to laminitis or insulin dysregulation.
Conclusion
Pasture-associated laminitis is not a random event but the result of metabolic stress that some horses are unable to handle adequately. Fructan levels fluctuate throughout the day and season, with cold mornings posing the greatest risk. Gradual adaptation, body condition monitoring, combining pasture with hay, and continuous access to water and mineral supplements significantly reduce the likelihood of laminitis development.
If you want, I can also polish this translation to sound more like a native veterinary/academic article in English (slightly smoother wording for publication or a website).
