Diurnal Variation in Forage Nutrient Composition of Mixed Cool-Season Grass, Crabgrass, and Bermudagrass Pastures.
Authors: Weinert-Nelson Jennifer R, Meyer William A, Williams Carey A
Journal: Journal of equine veterinary science
Summary
Warm-season grasses such as crabgrass and bermudagrass have gained attention as potential lower-sugar alternatives to traditional cool-season pastures, particularly for horses requiring NSC (non-structural carbohydrate) restriction due to conditions like equine metabolic syndrome or laminitis. Weinert-Nelson and colleagues collected forage samples at four-hourly intervals over three days from boot-stage mixed cool-season grass, crabgrass, and bermudagrass swards, then analysed their nutrient composition and soluble carbohydrate fluctuations throughout the day. Cool-season grass proved considerably higher in NSC at 17.6%, compared to just 10.6% for bermudagrass and 10.9% for crabgrass, whilst cool-season grass also delivered superior digestible energy (2.29 Mcal/kg) despite lower crude protein levels (16.1%). Perhaps most significantly, the diurnal pattern—where NSC peaks in afternoon and evening hours (14.5–14.9%) and dips in early morning (11.2–11.4%)—was substantially more pronounced in cool-season grasses than warm-season varieties, meaning the common practice of restricting grazing to early morning yields much greater benefit on conventional pastures. For equine professionals managing horses sensitive to high sugar intake, these findings validate warm-season grasses as genuinely lower-risk options throughout the day, whilst confirming that traditional pasture management strategies remain most critical when cool-season swards dominate the grazing landscape.
Read the full abstract on PubMed
Practical Takeaways
- •Warm-season grasses (crabgrass, bermudagrass) offer a practical low-NSC alternative to cool-season pastures for horses at laminitis risk, with NSC levels approximately 40% lower
- •If using cool-season pastures, restrict grazing to early morning hours when NSC is lowest (11.2-11.4%) rather than afternoon/evening (14.5-14.9%)
- •Diurnal NSC variation is much less pronounced in warm-season grasses, making them a more consistent and predictable forage option for metabolically compromised horses
Key Findings
- •Cool-season grass pastures contained significantly higher NSC (17.6%) compared to crabgrass (10.9%) and bermudagrass (10.6%)
- •NSC concentrations peaked in afternoon/evening (14.5-14.9%) and were lowest in early morning (11.2-11.4%) across all forage types
- •Diurnal variation in NSC was most pronounced in cool-season grasses versus warm-season grasses
- •Warm-season grasses (crabgrass and bermudagrass) may serve as alternative low-NSC pasture forages for horses where NSC intake is a concern