PSVI-15 Effect of direct-fed microbials on fecal characteristics during an acidosis induction

The objective was to investigate the effects of two direct-fed microbial dosing strategies on fecal characteristics of beef cattle during an acidosis challenge. Ruminal acidosis is a metabolic disorder in beef cattle that may contribute to hindgut acidosis. Eighteen ruminally cannulated steers (BW = 328 ± 20 kg) were used in a completely randomized design with 6 steers in each period. Two steers in each period were randomly assigned to one of three treatments: blank media (NCON), a single strain of Megasphaera elsdenii at 108 CFU (DFM1), and a combination of Megasphaera elsdenii and proprietary microbial strains at 1010 CFU per dose (DFM2). On d 1, DFM1 was dosed once and DFM2 and NCON were dosed daily at 0700 on d 1-15. A basal diet (45% forage) was fed ad libitum on d 1-7. To induce acidosis, steers were fasted for 24 h on d 8 and were fed the challenge diet (10% forage) ad libitum on d 9-15. Fecal pH was measured throughout the challenge and total feces was collected on d 11-14 to determine washed fecal particle size and observe mucin casts. Fecal pH and mucin cast score was not affected (P ≥ 0.29) by treatment. Fecal particle size in DFM1-treated steers was greater (P = 0.01) than NCON and DFM2. Fecal particle size tended (P = 0.06) to increase over time. Fecal particle size was not correlated (P ≥ 0.56) to ruminal or fecal pH. Fecal mucin cast score was positively correlated to dry matter intake (P < 0.01) and mean ruminal pH (P = 0.06). Mucin cast score may help in monitoring ongoing bouts of ruminal acidosis. Overall, results indicate direct-fed microbial treatment affected fecal particle size but not fecal pH and mucin cast score during an acidosis challenge.