Technical Abstract: Anecdotal observations suggest increased incidences of metabolic problems in horses on pasture after a frost. The speculation is that frost increases the level of nonstructural carbohydrates (NSC) in cool-season grasses, which have been implicated in horse metabolic problems (e.g., laminitis). We conducted a preliminary study to test the hypothesis that frost increases NSC levels in cool-season grasses. The NSC levels were similar among bluegrass, ryegrass, and tall fescue. Orchardgrass had lower NSC levels that the other grasses. The NSC levels increased in bluegrass, orchardgrass, and ryegrass after the 24 hour simulated frost. Tall fescue NSC decreased slightly after frost. Thus, the speculation that frost causes increased NSC levels in cool-season grasses may have some validity. Would the additional small increase after a frost be enough to trigger the metabolic problem? Based on this preliminary study, we conclude that frost slightly increases NSC levels in cool-season forages. We do not know if this increase is enough to trigger metabolic problems in horses.