LAUSR

The objective of this study was to evaluate the effect of adding monensin into high-concentrate diets based on either finely-ground or high-moisture corn during the transition from adaptation to finishing diets on ruminal pH of cannulated Angus and Nellore steers. Four 30-mo-old Nellore and four 30-mo-old Angus steers were divided (± 550 kg) into two 4 x 4 Latin squares, where each square was composed by animals from same breed, and randomly submitted to a 2 x 2 factorial arrangement of treatments as follows: T1) Finely-ground corn + monensin; T2) Finely-ground corn; T3) High moisture corn + monensin; T4) High-moisture corn. Periods were divided as follows: 14 days of adaptation diets and 18 days of finishing diet (80% concentrate). The study lasted 149 days, including three 7-d washout intervals. The rumen pH was assessed continuously via data loggers on days 4, 8, 12, 16, 20, 24 and 28. Interactions between breed and days were observed for DMI (P = 0.02) and pH duration below 5.6 (P = 0.01), where Angus steers had greater DMI and spent a longer time below 5.6 than Nellore animals on days 12, 16, 20, 24 and 28. The addition of monensin decreased (P = 0.01) DMI on days 16, 20, 24 and 28. Regarding pH duration and area below 5.6, an interaction between breed and corn was observed (P = 0.001), in which Angus steers fed finely-ground corn spent a longer time (416 min/day) and had a larger area (224.6 min x pH units/day) below 5.6 than animals from other treatments. For mean pH, steers consuming high-moisture corn had higher pH (6.45 vs. 6.29); and an interaction was observed (P = 0.03) between breed and monensin, where monensin addition decreased pH for Angus (5.96 vs. 6.18), but not for Nellore steers (6.68 vs. 6.63). The feeding of monensin and finely-ground corn did not positively impact rumen pH of Angus steers.