<p>Sixteen Angus crossbred steers were used to determine the impact of trace mineral (TM) source, diet type, and monensin and tylosin supplementation on rumen fermentation characteristics. Experiment 1: Steers were adapted to a finishing diet before being assigned dietary treatments. A 2 × 2 factorial arrangement of treatments was utilized with factors: (1) TM source (sulfate; STM or hydroxy; HTM) and (2) with or without monensin and tylosin (MT). Following the 28-day feeding period, rumen samples were collected at 0, 2, and 4&#xa0;h post-feeding. Experiment 2: Steers were adapted to a lactating dairy cow diet and assigned dietary treatments for 28&#xa0;days. A 2 × 2 factorial arrangement of treatments was utilized. Factors included (1) TM source (STM or HTM) and (2) with or without monensin (M). On day 29, rumen samples were collected at 0, 2, and 4&#xa0;h post-feeding. Rumen fluid samples from both experiments were analyzed for short chain fatty acids (SCFA), pH, and ammonia concentrations. Experiment 1: Molar proportions of acetate were lesser (<i>P</i> &lt; 0.04) and propionate greater (<i>P</i> &lt; 0.01) in steers receiving HTM compared to steers receiving STM. Experiment 2: Total SCFA production was greater (<i>P</i> &lt; 0.01) in steers supplemented with HTM compared to STM. Supplementation of M reduced the molar proportion (<i>P</i> &lt; 0.01) of acetate and increased (<i>P</i> &lt; 0.05) molar proportions of propionate and butyrate. These data indicate that TM source and M may modulate rumen fermentation characteristics but their impacts on rumen fermentation may be diet dependent.</p>