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.