During spring and summer months, it is important for horse owners to be aware of the risks of the consumption of too much grass especially by horses that have health problems such as laminitis and other nutrition-related diseases.
Research shows that some horses face serious metabolic upsets that are triggered by consumption of the sugars in fresh grass. Owners of such horses need to be aware of the health consequences.
Throughout history horses have enjoyed unrestricted grazing, but with new strains of forage, heavy fertilization of pastures, newly diagnosed metabolic complaints, and problems with equine obesity, grass has come under closer scrutiny.
Season of the year, rainfall, temperature, frequency of mowing, plant types, and grazing pressure influence the sugar levels in pasture plants. For extremely sensitive horses, there is no completely safe time to graze. These horses are best managed on low-carbohydrate hay.
During daylight hours, grasses manufacture and store sugars as they absorb water, sunlight, and carbon dioxide. These stored sugars are used to fuel plant growth during the night. Because of this growth process, sugar levels are at their highest in late afternoon and at their lowest in the very early morning hours.
Horses that are sensitive to carbohydrate levels in pasture grass can graze with least risk from the predawn hours until around 10:00 a.m. This is a time period when stored sugars have been used and have not yet been replenished by photosynthesis.
Sensitive horses should not be allowed to graze when sugars are being built up and stored, usually during the sunlight hours and through the early hours of the night.