PSI-10 - Relationships Between Fecal Characteristics, Rumen pH, and Intake During an Acidosis Challenge

Abstract: The objectives were to: 1) determine the relationship of fecal particle size with rumen pH, fecal pH, dry matter intake (DMI) and 2) determine the ability of fecal characteristics to predict rumen pH and DMI. Decreased ruminal pH during an acidotic bout may reduce fiber digestion and increase subsequent washed fecal particle size. Data were collected in a metabolism experiment using eighteen ruminally cannulated steers. The study was a completely randomized design evaluating the effect of a lactate adaption before an acidosis challenge. Ruminal pH, DMI, and fecal characteristics (fecal pH and washed fecal particle size) were measured for 4 days after the acidosis challenge. Fecal particle size was measured with 7 sieves with diameters ranging from 4750 to 600 µm. Average rumen pH over 4 days was associated (r = 0.60; P < 0.01) with mean fecal particle size. However, rumen pH was not correlated with fecal pH (P > 0.1). Fecal pH was not correlated with mean fecal particle size (P > 0.1). Mean fecal particle size was correlated with days after the acidosis challenge (r = 0.36; P < 0.01). Multiple regressions were performed with the GLMSELECT procedure of SAS 9.4 using stepwise selection. Rumen pH was best predicted (r² = 0.22) by fecal particle size between 1700 and 1400 µm, 1180 and 850 µm, and less than 600 µm. Dry matter intake was best predicted (r² = 0.17) by fecal particle size between 2360 and 1700 µm, 1400 and 1180 µm, and 850 and 600 µm. Overall, results indicated mean fecal particle size was correlated with rumen pH and days after the acidosis challenge. Additional data are needed for fecal characteristics to accurately predict ruminal pH and DMI.