Evaluation of the Effect of Maturity On Switchgrass Hay WHEN FED to Beef Cattle in Kentucky.

Kentucky producers have recently shown interest in using switchgrass (Panicum virgatum) as a dual purpose crop for both forage for feeding cattle and biomass.  The objective of this study was to evaluate the effect of maturity on switchgrass hay digestibility when fed to beef steers. In this study, 'Alamo' and 'Cave-in-Rock' switchgrass were harvested for hay at two different locations in Kentucky.  Each cultivar was harvested as hay at the late vegetative, mid-boot, and early flowering stages of maturity.  Hays were sampled and analyzed to determine quality.   Hays were individually fed to 500-600 lb Angus x Hereford steers to determine apparent in-vivo digestibility.  After an adjustment feeding period, fecal grab sampling using acid detergent insoluble Ash (ADIA) as an internal marker was used to estimate fecal output.   Digestion coefficients were then calculated to determine dry matter digestibility (DMD), neutral detergent fiber digestibility (NDFD), and crude protein digestibility.  Intake and digestion data were analyzed according to the REPEATED measures option in the MIXED procedure of SAS.  The LSMeans statement was used to calculate treatment means.  The model terms were treatment, block, time (i.e. collection period), and treatment x time.  Steer was considered the subject with compound symmetry as the co-variance structure.  Preliminary results suggest that stage of maturity at harvest has a significant effect on intake, DMD, NDFD, and digestible CP.  They also suggest that mean intake, DMD, NDFD, and digestible CP were greatest for hays harvested at the late vegetative stage of maturity.  Few differences were observed in mean intake, DMD, and NDFD between the latter two harvests.  These data suggest that switchgrass should be harvested as hay no later than at the late vegetative stage.  Delaying harvest of switchgrass hay to the mid-boot, or flowering stages will reduce animal performance.