With springtime comes warm, sunny days and an abundance of lush, green pasture, as well as an increased incidence of laminitis and colic. Fresh pasture can be a great source of relatively inexpensive nutrition for horses. A well-managed pasture can cost as much as a third less than feeding hay. Access to pasture also provides horses with exercise and an opportunity for natural grazing behaviors.
However, fresh pasture can also pose a few problems. The switch from hay to pasture can be a relatively dramatic change in the horse’s overall diet, with the potential to cause digestive upset. The nutrient composition of hay and pasture can be quite different, particularly in terms of nonstructural carbohydrate content.
The term nonstructural carbohydrate (NSC) is used to describe the nonfibrous carbohydrates found in plant material. In equine nutrition, NSC includes sugars and starch. Alternatively, the term structural carbohydrate is used to describe the fibrous carbohydrates that are more slowly fermented in the hindgut of the horse.
Research has shown that NSC accumulates in plants throughout the course of a day as a result of normal photosynthesis. Once the plants energy requirement has been met, any additional sugars produced are stored for later use. Once the sun sets, photosynthesis ceases, forcing the plant to rely on stored NSC for energy. This reliance gradually depletes the plants energy reserves over the course of the night. Consequently, NSC levels are highest in late afternoon and lowest in early morning hours. Plant maturity also affects NSC content; immature forage will have higher NSC levels than mature forage because, as the plant matures, nonstructural carbohydrates are gradually replaced with structural carbohydrates.
Sudden increases in intake of NSC (like that associated with over-consuming lush pasture) may lead to increased incidence of laminitis and colic. Consequently, it’s important to transition horses slowly from hay to pasture; start by allowing horses access to pasture for about 30 minutes a day for the first few days and gradually increase the duration of their grazing time over the course of two to three weeks. One way to prevent horses from gorging themselves when turned out to pasture is to feed them hay first. This way, they’re already full and physically limited to how much grass they can consume.
Extra precautions should be taken with horses that are particularly sensitive to NSC levels (i.e. those with a history of laminitis, insulin resistance, Cushing’s disease, polysaccharide storage myopathy [PSSM], or equine metabolic syndrome [EMS]). For these horses, it is recommended that spring grazing time be eliminated altogether or grazing be reduced to a few hours per day until pasture forages have matured and NSC content has decreased.
Both manufactured horse feeds and straight grains can contribute to the NSC content of the overall diet. Co-op Pinnacle Horse Feeds have been formulated to contain lower levels of NSC, with one product in particular designed for horses that are sensitive to NSC levels: Pinnacle Low Starch (#319PE).
Unfortunately, both laminitis and colic have been associated with the lush, spring pasture we look forward to each year. Consider your current management strategies and the horses under your care. Do you need to make adjustments to your management program to help prevent these potentially devastating conditions on your farm?