53 Relationships Between Fecal Characteristics, Ruminal Ph, Intake and Digestion in Feedlot Cattle

Abstract

Abstract The objectives were to: 1) determine the relationship of fecal characteristics with ruminal pH, dry matter intake (DMI) and dry matter digestion and 2) determine the ability of fecal characteristics to predict ruminal pH, DMI, and dry matter digestion. Data were collected in two metabolism studies using eighteen ruminally cannulated steers (n = 36). Each study was a completely randomized design evaluating the effect of a direct-fed microbial during an acidosis challenge. Ruminal pH, DMI, total tract DM digestion and fecal characteristics (fecal pH, washed fecal particle size and mucin casts) were measured for 4 d after the acidosis challenge. Rumen pH was not correlated (P ≥ 0.15) with mucin cast score or mean fecal particle size but was negatively associated with fecal pH (r = -0.42; P < 0.01). Total tract DM digestion was correlated (r ≥ 0.53; P ≤ 0.02) to fecal pH and fecal particle sizes between 1180 and 2360 µm. Dry matter intake was correlated (r ≥ 0.41; P < 0.01) to mean fecal particle size and fecal particle sizes between 2360 and 4750 µm. Multiple regressions were performed with the GLMSELECT procedure of SAS 9.4 using stepwise selection. Ruminal pH was best predicted (r2 = 0.20) by fecal pH and fecal particle size between 1400 and 1700 µm. Total tract DM digestion was best predicted (r2 = 0.92) by fecal pH, mucin cast score, and fecal particle size between 3350 and 1700 µm. Dry matter intake was best predicted (r2 = 0.51) by mean fecal particle size, fecal pH and fecal particle size between 1400 and 850 µm. Overall, results indicated fecal pH was correlated to ruminal pH and total tract DM digestion. Fecal characteristics including washed particle size can also predict total tract DM digestion in feedlot cattle.