Effects of monensin inclusion and the subspecies of cattle on utilization of bermudagrass hay (13.7% CP) were evaluated using ruminally cannulated steers (5 Bos indicus, BI and 5 Bos taurus, BT; 398 kg BW). Subspecies were concurrently subjected to a 2 period, 2 treatment crossover design. Treatments consisted of 0 (CON) or 200 (MON) mg·hd⁻¹ monensin (Rumensin 90; Elanco Animal Health, Greenfield, IN) fed daily in 0.91 kg DDGS. Steers were group housed during adaptation periods and moved to individual covered pens to facilitate sampling. Periods were 70 d in length allowing 42 d adaptation, and 28 d withdrawal between periods. Ruminal fluid was collected with a suction-strainer 0, 2, 4, 8, and 12 h after feeding on d 42 for analysis of pH, VFA, and ruminal ammonia-N. Ruminal contents were squeezed through 4 layers of cheesecloth into insulated containers 2 h after feeding on d 42 for determination of rate of ammonia production and CH₄-producing activity. No subspecies × treatment interactions were observed (P ≥ 0.14). There was an effect of time after feeding (P ≤ 0.01) on pH, ruminal ammonia-N, total VFA, acetate:propionate, and molar percentages of acetate and propionate. Total VFA concentration was greater (P = 0.01) in CON vs. MON steers (66.5 vs. 62.0 mM). Total VFA concentration was similar (P = 0.28) for BI and BT subspecies (62.7 and 65.8 mM, respectively). Monensin decreased the molar percentage of acetate (P = 0.02) from 72.5% to 71.2% and increased the molar percentage of propionate (P < 0.01) from 16.9% to 18.7%, reducing (P < 0.01) the acetate:propionate ratio from 4.34 to 3.85. Although CH₄- producing activity was not significantly different (P = 0.19) between CON and MON, monensin feeding resulted in a 15.8% reduction in CH₄-producing activity. Bos indicus steers had greater (P = 0.07) CH₄-producing activity than BT steers (21.37 vs. 16.62 μmol CH₄·mL⁻¹·h⁻¹). Monensin had no effect (P ≥ 0.19) on pH, ruminal ammonia-N, or rate of ammonia production. Overall, monensin decreased the acetate:propionate ratio by decreasing acetate and increasing propionate and numerically reduced CH₄-producing activity. Bos indicus had greater CH₄-producing activity compared with BT steers.