Determination of forage quality and in situ digestibility of miscanthus over time

Abstract Text: Miscanthus, a C4, perennial grass, may be a potential bioenergy source due to plant yield and hardiness. Excellent yields during early growing stages means miscanthus may also be an alternative forage for ruminants. We hypothesized that early cuttings of Miscanthus would be more digestible in ruminants, and have reduced NDF and ADF concentrations and greater CP concentrations than samples taken later in the growing season. Therefore, objectives of this study were to evaluate forage characteristics and in situ digestibility of 3 miscanthus varieties: (1) Miscanthus sacchariflorus (Blumel), (2) Miscanthus xgiganteus (Illinois), and (3) Miscanthus sinensis (Emerald Shadow; Emerald), over time. Samples were taken at 2 wk intervals over 8 wk. Samples were harvested from randomly selected, non-border plants from 4 different plots per variety per time point, to minimize field effects. Samples were analyzed for DM, NDF, ADF, and N. Digestibility was determined by in situ DM disappearance (DMD) and NDF disappearance (NDFD). Field replications of each variety, composited by time, were placed in ruminally fistulated steers (n = 2). After 48h incubation, in situ bags were dried at 55°C for 3d, weighed, then composited for 105°C DM and NDF analysis. Data were analyzed via the MIXED procedures of SAS (SAS Inst. Inc., Cary, NC). There was an interaction (P ≤ 0.03) of variety and week sampled for ADF and NDF concentrations. Over time, ADF and NDF concentration of Emerald increased at a slower rate than either Blumel or Illinois. There was no variety by week interaction (P = 0.38) for CP concentrations; however, CP decreased (P < 0.01) over time in all varieties. Mean CP concentrations were greatest (P < 0.01) in Emerald and not different in Illinois and Blumel (8.72, 7.89, and 7.96%, respectively). There was an interaction (P < 0.01) of variety and week for DMD. While all varieties decreased from wk 2 through 6, Emerald DMD continued to decrease from 6 to 8 wk but Illinois and Blumel increased. There was a variety by week interaction (P = 0.05) for NDFD. Illinois and Blumel NDFD decreased at a faster rate than Emerald for the first 6 wk. Increasing NDF and ADF concentrations, coupled with decreasing CP and in situ disappearance suggest that forage quality of miscanthus decreases over time, reducing its desirability as an alternative forage for cattle.

Keywords: cattle, forage quality, miscanthus