Date of this Version
Crop Sci. 30:1313-1320
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°/o 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.