Fiber digestion dynamics of sward components within switchgrass populations

Forage quality as it relates to plant maturity is well established; however , strategies for improving fiber digestion in switchgrass populations have not been determined. The objectives of this study were to determine fiber d igestion of sward components within switchgrass (Panicum virgatum L.) popul ations and which aspects of fiber digestion dynamics caused in vitro dry ma tter disappearance (IVDMD) differences of six switchgrass populations, This study was conducted in 1993 near Ames, LA, and Mead, NE. The experimental design was a randomized complete block design with a split-plot arrangement of treatments with four replicates at each location. Whole plots were popu lations and subplots were sward maturity. 'Trailblazer', 'Pathfinder', 'Cav e-in-Rock', and three experimental switchgrass populations were used in thi s study. Populations were harvested on 9 June, 19 July, and 27 August at Am es and on 10 June, 27 July, and 36 August at Mead, Fiber composition and di gestibility were determined on leaf blade, leaf sheath, and stem fractions of the primary growth stages, Significant differences for theoretical true digestibility (TD) and neutral detergent fiber (NDF) existed for morphologi cal components at each sward maturity, However, digestion characteristics o f the sward components were not stable across primary growth stages. Rate o f fiber digestion was faster for most sward components at Ames than Mead, a lthough stems of elongating tillers from elongating swards digested faster on plants grown at Mead than Ames. Rate of fiber digestion of stems was typ ically slower than either leaf blades or sheaths, but in several instances they were similar or stems had faster rates of fiber digestion. Although ph enotypic selection can increase fiber digestibility, plant maturity remains an important factor, and selections may require evaluation at different st ages of morphological development, Thus, improvements in forage digestion, at least in switchgrass, may only he manifested for the growth stage at whi ch it was selected.