Effects of bismuth subsalicylate and calcium-ammonium nitrate on in vitro fermentation of bahiagrass hay with supplemental molasses

Abstract Text: A randomized complete block design was used to determine the effects of increasing amounts of bismuth subsalicylate (BSS) and calcium-ammonium nitrate (CAN) on in vitro fermentation of bahiagrass hay (Paspalum notatum). Serum bottles (125-mL) containing 100 mL of a 4:1 buffer:ruminal fluid inoculum and 0.7 g of an 80:20 bahiagrass hay:molasses substrate (DM basis) were incubated for 48 h. Three d (block) of incubation were performed. Treatments were arranged as a 4 × 3 factorial with 4 concentrations of BSS (0.00, 0.33, 0.66 and 1.00% of diet DM) and 3 concentrations of CAN (0.0, 1.2 and 2.4% of diet DM). Treatments were made isonitrogenous with urea. Two ruminally cannulated crossbred steers (348 ± 29 kg BW) fed bahiagrass hay ad libitum and 2.27 kg/d (as is) of a 50:50 molasses:crude glycerol mixture, were used as ruminal fluid donors. In vitro OM digestibility (IVOMD) was determined in a separate set of tubes. Data were analyzed using PROC MIXED of SAS with fixed effects of BSS, CAN, BSS × CAN, and random effect of day. Gas production and IVOMD were linearly decreased (P ≤ 0.001) as CAN and BSS increased. Ammonia-N was linearly decreased (P = 0.001) as CAN increased. Methane production (mmol/g substrate fermented) was linearly reduced (P < 0.001) as CAN and BSS increased. Both CAN (P = 0.032) and BSS (P < 0.001) reduced H₂S production, with 0.33% BSS reducing production by 61% compared with 0.00%. There was no effect (P > 0.05) of CAN on concentrations or molar proportions of any VFA analyzed. As BSS increased, concentration of acetate (P = 0.002), propionate (P = 0.007), and total VFA (P = 0.003) decreased linearly.  When comparing treatment means, no difference (P = 0.119) in total VFA was observed between 0.33% and 0.00% BSS. The acetate:propionate (A:P; P = 0.005) and molar proportions of acetate (P = 0.041), and propionate (P = 0.005) were quadratically affected by BSS inclusion, where 0.33% BSS decreased A:P compared with 0.00% BSS (P= 0.050). Including BSS at 0.66% and 1.00% of the diet DM had negative effects on in vitro fermentation of bahiagrass hay. However, when BSS was included at 0.33%, A:P was decreased and total VFA concentrations were unaffected. Nitrate inclusion reduces methane production without negatively affecting fermentation. A combination of BSS and CAN may favorably affect ruminal fermentation while decreasing methane emissions.

Keywords: Bismuth subsalicylate, nitrate, fermentation