Alkali‐Labile Cell‐Wall Phenolics and Forage Quality in Switchgrasses selected for Differing Digestibility

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Abstract
Alkali‐labile cell‐wall phenolics have been implicated in previous research as factors that affect forage digestibility by ruminants. Alkali‐labile cell‐wall phenolics, in vitro dry matter digestibility (IVDMD), neutral‐detergent fiber (NDF), acid‐detergent fiber (ADF), lignin (permanganate‐oxidation), and crude protein (CP) were determined in three switchgrass (Panicum virgatum L.) strains differing genetically for IVDMD to determine relationships between these quality parameters and IVDMD during the grazing season. Grazed (upper 1/3 of grazed plants) and ungrazed (whole plants in caged exclosures) forage was collected weekly from replicated 0.4− ha pastures of ‘Trailblazer’ (high IVDMD), ‘Pathfinder’, and a low‐IVDMD strain during three grazing seasons from 1983 to 1985. The principal alkali‐labile phenolics (g kg−1 NDF) detected were p‐coumaric acid (PCA) and ferulic acid (FA). Increased PCA concentration due to increased maturity averaged >70% during each grazing season and corresponded with increased NDF, ADF, and lignin and decreased IVDMD, CP, and FA/PCA ratio. Ferulic acid concentration either declined slightly or remained unchanged. Averaged across 3 yr, Trailblazer had higher (P < 0.06) IVDMD, lower (P < 0.09) PCA and higher (P < 0.10) FA/PCA ratio than a divergently selected low‐IVDMD strain. Differences between strains in detergent‐fiber constituents, FA, and CP were either not apparent or inconsistent with strain differences in IVDMD. Results were consistent with both grazed and ungrazed switchgrass and indicate that alkali‐labile cell‐wall phenolic composition in switchgrass is heritable and genetically correlated to IVDMD.