Evaluation of perennial switchgrass as a replacement for cornstalks in high sulfur beef cattle diets

Abstract Text: Perennial switchgrass is a bio-renewable energy resource, and may serve as a roughage source in feedlot diets. Mature switchgrass is a very low quality feedstuff, but alkali treatments have been shown to increase its digestibility. This study determined the effects of untreated and alkali treated switchgrass on cattle growth performance, ruminal pH and hydrogen sulfide concentrations when used as a replacement for cornstalks in diets calculated to contain 0.5% S.  Thirty-six Angus-cross steers (430.6 ± 30.55 kg, SD) were blocked by BW to pens with feed bunks capable of recording individual intake (12 steers per treatment). Pens (6 steers per pen) were assigned to one of the following high-S, corn-based diets, where roughage was provided by: 1) chopped corn stalks (11.5% of diet DM; providing 10% NDF from roughage), 2) chopped untreated switchgrass (11.8% of DM; 10% roughage NDF), or 3) chopped switchgrass treated with calcium hydroxide (added at 7% of DM) for 1 wk before feeding (11.8% of DM; matching untreated switchgrass inclusion).  Weights were recorded on two consecutive days at the start and end of the 88 d trial. Data were analyzed using Proc Mixed in SAS, with steer as the experimental unit and the fixed effect of diet and block. Analyzed as repeated measures, ruminal pH and hydrogen sulfide concentrations collected on d 14, 21, 35, and 42 at 6 hr post-feed delivery were not affected by the treatment × time interaction (P ≥ 0.11). Steers fed untreated switchgrass had greater (P = 0.02) ruminal pH than steers fed cornstalks, but pH was not different (P ≥ 0.29) between any other treatments.  Ruminal hydrogen sulfide concentrations were unaffected by diet (P = 0.57). Final BW was not affected by treatment (P = 0.84). Overall ADG was consistent between treatments (P = 0.66), as was DMI (P = 0.92) and G:F (P = 0.61). There were no differences between treatments (P ≥ 0.43) for HCW, backfat thickness, ribeye area, marbling score, or calculated yield grade. Based on these results there is no apparent benefit to alkali treatment of switchgrass when used at low inclusions in concentrate-based diets, and mature switchgrass may replace cornstalks under these conditions. 

Keywords: cattle, sulfur, switchgrass