Treatment of mature switchgrass and cornstalks with calcium hydroxide and comparison of untreated mature switchgrass and cornstalks as roughage in beef cattle feedlot diets

Abstract Text: An in situ digestibility study was completed to evaluate the effect of calcium hydroxide treatment of switchgrass and cornstalks.  Bales of cornstalks and mature switchgrass were ground to pass a 17.78 cm sieve and water was added to achieve 60% DM.   A 2 x 2 x 2 factorial of treatments was utilized with the factors of roughage source (cornstalks or switchgrass), chemical treatment (none or calcium hydroxide at 7%), and duration of incubation (1 or 4 wk). After the allotted time, barrels were emptied and samples were collected, dried, ground (1 mm screen), weighed, and placed into Dacron bags (n = 3 bags·sample^-1time point^-1). Bags were incubated in the rumen of a cannulated steer for 24, 36, or 48 h, then dried and weighed.  There was an interaction between treatment and wk (P < 0.001). Digestibility of both roughages was improved by chemical treatment and wk of chemical treatment (P < 0.0001); however, digestibility of untreated cornstalks did not differ due to wk of incubation (P > 0.2) while untreated switchgrass digestibility tended to be lesser after 4 wk of incubation (P = 0.15).   A feeding trial using 121 crossbred steers (380 kg initial BW) was also conducted to evaluate the utilization of untreated mature switchgrass as a roughage source in feedlot diets.  Steers were randomly allocated to 1 of 4 pens (n = 30 or 31 per pen), with 2 pens receiving cornstalks  (STALK) and 2 pens receiving switchgrass (SWITCH) at 14.2% of diet DM.  Cattle were fed for 131 days with Revalor IS implants administered on d 27 and d 77 of the feeding period, and Optaflexx fed the final 32 d on feed at 300 mg·steer^-1d^-1.  Cattle were marketed on a common date and carcass data were collected.   Data were analyzed using the MIXED procedure of SAS.  When compared to STALK cattle, SWITCH cattle had lesser marbling scores (P = 0.0095).  Backfat, HCW, KPH, ribeye area, and yield grade did not differ between treatments (P ≥ 0.19).  Additionally, carcass-adjusted ADG did not differ between treatments (P = 0.43).  Cattle fed SWITCH had lesser DMI than did STALK cattle (P = 0.0004) but G:F did not differ between treatments (P = 0.9783).  In summary, untreated switchgrass may replace cornstalks at low inclusions in finishing diets, and digestibility of this low quality roughage may be improved through alkaline treatment.   

Keywords: Switchgrass, Feedlot, Digestibility