Effects of Harvest Date, Sampling Time, and Cultivar on Total Phenolic Concentrations, Water-Soluble Carbohydrate Concentrations, and Phenolic Profiles of Selected Cool-Season Grasses in Central Kentucky.
Authors: Kagan Isabelle A, Goodman Jack P, Seman Dwight H, Lawrence Laurie M, Smith S Ray
Journal: Journal of equine veterinary science
Summary
Understanding how forage phenolic and water-soluble carbohydrate (WSC) concentrations fluctuate across the grazing season is critical for managing horses prone to metabolic conditions, yet little research has characterised these compounds in commonly used cool-season grass cultivars. Researchers in Kentucky sampled five grass varieties ('Linn' and 'Calibra' perennial ryegrass, 'Cajun II' tall fescue, 'Persist' orchardgrass, and 'Ginger' Kentucky bluegrass) at morning and afternoon intervals across late April, early May, and late May, quantifying total phenolics and WSC whilst profiling individual phenolic compounds using high-performance liquid chromatography and mass spectrometry. Afternoon grazing offered significantly higher WSC across all cultivars, with afternoon concentrations varying among varieties and declining substantially by late May (P <0.0001); phenolic concentrations showed distinct patterns, generally decreasing or remaining stable from late April onwards except in Persist orchardgrass, and declining further in afternoon samples of Persist orchardgrass and Calibra perennial ryegrass (P = 0.015). The five cultivars exhibited markedly different phenolic profiles—with Calibra and Linn perennial ryegrass plus Cajun tall fescue clustering together whilst Ginger bluegrass and Persist orchardgrass showed distinct compound compositions—suggesting phenolic diversity that may modulate palatability and potentially interact with WSC effects on equine metabolic health. These findings indicate that forage management strategies should account for both harvest timing and cultivar selection, particularly for insulin-dysregulated horses, and warrant further investigation into how individual phenolic compounds influence nutrient uptake and metabolic responses.
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Practical Takeaways
- •Morning grazing may reduce WSC intake for horses at metabolic risk (laminitis-prone), as afternoon WSC concentrations are significantly elevated in cool-season pastures
- •Grass cultivar selection matters: Persist orchardgrass and Calibra perennial ryegrass showed distinct phenolic profiles and temporal patterns that may influence forage safety and palatability for individual horses
- •Phenolic compounds vary by cultivar and time of day, suggesting potential interactions with WSC that warrant further investigation for horses with metabolic or digestive sensitivities
Key Findings
- •Water-soluble carbohydrate concentrations were significantly higher in afternoon samples (P < 0.0001) across all grass cultivars
- •Total phenolic concentrations were initially highest in Calibra perennial ryegrass and Persist orchardgrass but decreased or remained constant from late April to late May (P < 0.0001)
- •Phenolic profiles differed significantly between cultivars, with Calibra PRG, Linn PRG, and Cajun tall fescue sharing similar profiles distinct from Ginger Kentucky bluegrass and Persist orchardgrass
- •Afternoon sampling showed decreased total phenolics in Persist orchardgrass and Calibra PRG (P = 0.015)