Owners with horses prone to laminitis should try to avoid grazing their horses at the end of the day, when grasses peak in NSC concentrations.
Non-structural carbohydrates (NSC) are often associated with increased risk of laminitis and insulin resistance in horses. NSC are highly fermentable carbohydrates and excessive consumption can lead to negative consequences in horses such as accelerated hindgut pH which has been implicated in pasture associated laminitis. NSC are a component of all forage species, including cool-season grasses such as fescues, ryegrasses orchardgrass, bluegrass, and bromegrass. Concentrations of NSC can fluctuate throughout the growing season, in response to stresses (i.e. drought), and throughout each day, usually increasing during the daylight hours and falling during the night. The fluctuation in NSC throughout the day is due to the amount of photosynthetic activity occurring. Because of the potentially high NSC concentrations that can occur at different times of day, researchers from North Carolina State University wanted to obtain a better estimation of NSC concentrations and its role in pasture-associated laminitis. The goal of the study was to determine how time of day affected daily pasture NSC concentrations, fecal pH, fecal lactate concentrations, and total volatile fatty acid concentrations.
Twelve mature, idle, light-horse geldings were enrolled in the study during the fall and were rotated through 3 treatments. The three treatments consisted of 1) 24 hours of continuous grazing beginning; 2) 10 hours of grazing over-night beginning at 9 pm; and 3) 10 hours of grazing during full daylight beginning at 10 am. The highest pasture NSC concentrations occurred around 9 pm, peaking at 20% NSC. NSC content at 7 am was 17%. Fecal pH and volatile fatty acid concentrations and ratios were highest in the continuously grazed group. Time of day does effect grass NSC content without significantly influencing fecal pH and volatile fatty acid production.
Length of grazing did have an impact on fecal pH and volatile fatty acid production. Even though pH was lower in both of the 10-hour grazing groups, it was not low enough to be of concern for causing any detrimental health effects. This is most likely due to the fact that pasture NSC content likely did not reach high enough levels to induce any problems. However, owners with horses prone to laminitis should try to avoid grazing their horses at the end of the day, when grasses peak in NSC concentrations.
Summarized by Emily Glunk, MS, University of Minnesota