The objective of this study was to evaluate the effects on ruminal parameters of Nellore steers fed with high-grain diet using virginiamycin (VM) and monensin sodium (MON). Twelve Nellore steers (268 ± 38 kg BW) with ruminal cannula were used in completely randomized design with 2 treatments and 6 replicates. Treatments were defined by kind of additive used in diet, VM (25 ppm) and MON (30 ppm). The animals were kept in feedlot in individual pens for 21 d. Ruminal ammonia nitrogen (NH₃-N), short-chain fatty acids concentration (SCFA) and ruminal fluid pH were measured before feeding (T0), 6 and 12 h after feeding (T6 and T12, respectively). Animals were fed ad libitum twice daily with a diet containing 85% whole corn and 15% pelleted feed (soybean, minerals and the additive). Data are shown in Table 1. There were no effects (P > 0.05) on NH₃-N and SCFA concentration and pH values when MON or VM were added in diet. Acetate:propionate ratio (A:P) did not show differences (P > 0.05) between treatments. However, the pH value decreased after feeding for both treatments. In conclusion, VM and MON did not affect pH, NH₃-N, SCFA and A:P ratio, however, the pH values were next to 6 and there was not wide variation between the measurement times. Table 1. Ruminal parameters of Nellore steers fed with high-grain diet containing virginiamycin or monensin sodium

Ruminal pH	VM	MON	SEM	P-value
T 0	6.11	6.08	0.307	0.952
T 6	6.07	6.15	0.322	0.868
T 12	5.98	6.02	0.256	0.921
SCFA (mM)
T 0	120.34	114.99	5.073	0.476
T 6	103.74	100.00	3.969	0.534
T 12	108.95	105.23	4.025	0.536
A:P ratio
T 0	2.25	2.44	0.228	0.556
T 12	2.07	2.12	0.166	0.812
NH3-N (mg/dL)
T 0	9.28	8.76	1.491	0.813
T 6	12.31	12.98	3.28	0.889
T 12	10.63	13.88	1.545	0.187