Redox potential of cecum content of growing pigs and its relation with pH and VFA concentration

Digestive microflora is partly responsible for physiological gut conditions. Measurements of redox potential (Eh) and pH of digesta may give a basis for understanding microbial activity and dynamics of fermentation. However, few studies have assessed the Eh of the gastrointestinal tract of pigs. Twenty-four pigs of 30 kg BW were slaughtered to measure Eh and pH of cecum content in situ and to obtain samples of ileum, cecum, and colon contents for VFA determinations. Pigs had previously been fed with a nonmedicated starter feed for 5 wk. Measurements of Eh and pH were recorded first at 2 min and then at 5-min intervals for 35 min to estimate kinetics and the delay to reach stabilization of the Eh value. Cecum Eh rapidly decreased (P < 0.001) from -115 to -180 mV after 15 min of insertion of the electrodes and then slowly decreased until -185 mV at 35 min. Cecal pH started at 5.74 and decreased (P < 0.01) slowly afterwards until 5.53 after 35 min. The Eh value after stabilization was negatively correlated (r = -0.64; P < 0.001) with final pH. Acetic, propionic, and butyric acids accounted for 58.7, 24.0, and 12.8%, respectively, of total VFA production of cecum content. The VFA production of ileal content was lower (P < 0.001) when compared to cecum or colon (50.8, 142.1, and 130.8 mu mol/g, respectively) and a higher proportion of formic and lactic acids was detected (32.3 and 27.0%, respectively). Proportions of acetic and propionic acids were negatively (r = -0.53; P < 0.01) and positively (r = 0.66; P < 0.001) correlated with Eh, respectively. In conclusion, Eh measured after stabilization seemed to be a meaningful predictor of hindgut fermentative activity.