October 2025 Issue

EAST COAST EQUESTRIAN October 2025 28 By Laura Kenny, Equine Extension Educator, Penn State Extension The weather is getting cooler, the leaves are turning, our horses are feeling good. However, anyone who owns a laminitis-prone horse may dread this season because of the increased risk of laminitis from pasture forages. While the study of laminitis is ongoing, we have learned much that can help us manage our horses. For instance, we know that the horses at greatest risk of pasture-associated laminitis are those with metabolic conditions that affect their insulin levels. Normal horses can consume moderate and high amounts of starch and sugar with no problems; their hormonal systems properly regulate glucose and insulin levels. Horses with risk fac- tors such as obesity and insulin dys- regulation may have an abnormally high or prolonged insulin response to these same feeds, which can cause a bout of laminitis. If you have a horse that is prone to laminitis, your first line of defense is always your equine veterinarian. They can guide you through testing, management, and even medical treatment options. Nutritional and exercise management often do wonders for controlling insulin sen- sitivity. Your veterinarian can also advise you on whether your horse should be totally off fresh pasture or can have some controlled grazing, perhaps with a grazing muzzle to control intake. If your laminitis-prone horse has been cleared for grazing, you may be wondering when the safest time is to do so. By now, most of us know that sugars (more accurately, Non-Structural Carbohydrates or NSC which include sugars, starch, and fructans) are highest in pastures at certain times of day, but there are multiple other factors that affect NSC levels. Remember that NSC is the fuel source that plants create and use for growth, so plants will always contain some NSC. You may be wondering about testing grasses for NSC since it’s recommended for hay. Unfortunately, grass samples continue to lose NSC once cut unless they are frozen immediately and shipped on ice. Additionally, the turnaround time for analysis means that you’ll know what conditions were like a week or two ago, but not today. As you will see, they can vary greatly from day to day. The bottom line is that you can never precisely guess what the NSC level of a pasture is at any given time. There are simply too many factors at play at the same time. However, if you familiarize yourself with these factors, you can make some educated decisions about when to graze or dry lot your at-risk horse (with veterinarian clearance, of course). Time of Day Plants photosynthesize when the sun is shining and accumulate NSC throughout the day. At night, plants can use up these NSC for growth. This means that an average day has the highest NSC levels at sunset after a full day of photosynthesizing, and the lowest NSC levels at sunrise after a night of NSC utilization.As a result, early morning hours are generally the safest time to graze. However, keep in mind that when overnight tem- peratures fall below 45°F, NSC utilization slows down and levels may still be high the next morning. A series of sunny days followed by cold nights can result in ex- tended high NSC levels in pastures. This is a common scenario in the autumn. Season Research has shown us that NSC levels follow a sea- sonal pattern as well. NSC is highest in the early spring, dips in the summer, and is moderate in the fall. Keep in mind that other weather patterns and environmental conditions can create exceptions, such as drought in the summer or sunny days followed by cold nights in the fall. Forage Type Pasture forages may be grasses or legumes, warm-season or cool-season. These categories affect their nutrition and NSC levels. Legumes, like alfalfa and clover, tend to have the highest calorie and protein lev- els, but they are not capable of accumulating excessive amounts of NSC. Cool-season grasses that we typically grow in Pennsylvania and other Northeast states, like timothy, orchardgrass, fescue, and Kentucky bluegrass, are on average lower in calories and protein than legumes but can accumulate unlimited amounts of NSC. Finally, warm-season grasses such as bermudagrass, teff, and crabgrass tend to contain the lowest calorie and protein levels and cannot accumulate very high levels of NSC. Among the commonly planted cool-season grass species we use for pastures, research has not shown that one consistently has lower NSC than others. However, perennial ryegrass has been bred for high NSC levels, so this grass often contains higher NSC than others. Temperature Cool-season grasses tend to contain higher NSC levels during cool weather compared to warm weather. Warm-season grasses may have small NSC fluctuations based on temperature, but overall do not vary as much as cool-season grasses. Sunlight If photosynthesis is what drives NSC production, then days or areas with less sun may be safer for at-risk horses. Cloudy days or shady paddocks may have lower NSC levels compared to sunny ones. Environmental Stress Any stressors that prevent forage growth and there- fore NSC utilization will cause NSC to accumulate until the stressor is removed. One example is drought. The plant continues to photosynthesize and store NSC, but cannot grow and utilize them until water is replenished. Another example is low soil fertility, and yet another is overgrazing. Try to avoid grazing cool-season grasses below 3 inches in height, where they store their NSC reserves. As you can see, there are too many competing fac- tors to accurately predict a pasture’s NSC level at any given time. But if you can identify when these factors are increasing the NSC level of your pasture, then you can make better decisions about when your at-risk horses graze. Don’t forget to discuss your grazing plan with your veterinarian! Laura Kenny has served in extension roles in New Jersey and Pennsylvania since 2008. She has worked as an equine educator at Penn State for the past seven years. Her primary focus is on improving environmen- tal stewardship on horse farms. She also contributes to programs on horse health, forage quality and training conservationists to successfully work with horse farms. Spring May be Green, But Fall is the Season of Sugar Did you know that East Coast Equestrian provides a Calendar of Events covering 3 months of action and horse community?