Alteration of Acid-Binding Capacity of Various Nursery Pig Diets and Its Influence on Properties of Digesta Along the Gastrointestinal Tract.

The objective of this study was to investigate the effects of reduced dietary acid-binding capacity (ABC) by acidifiers on the properties of digesta along the gastrointestinal tract of pigs. In Exp. 1, 144 pigs at 21 d of age [6.5 ± 0.9 kg body weight (BW)] were housed in pens (3 pigs/pen). In Exp. 2, 540 pigs weaned at 21 d of age (6.9 ± 0.9 kg BW) were housed in pens (3 barrows and 3 gilts/pen). In Exp. 1, the basal diet was supplemented with 0.25% bacitracin methylene disalicylate, 0.30 or 0.50% lactic acid-formic acid blend, or 0.30% lactic acid-formic acid-benzoic acid blend. In Exp. 2, the basal diet was supplemented with 0.25% bacitracin methylene disalicylate, 0.25, 0.35, or 0.50% benzoic acid, or 0.30, 0.40, or 0.60% sodium benzoate. In both Exp. 1 and 2, pigs were fed diets in 3 phases: phase 1 (7 d in both Exp. 1 and 2), phase 2 (14 d in Exp. 1 and 17 d in Exp. 2), and phase 3 (21 d in Exp. 1 and 17 d in Exp. 2), respectively. The range of ABC at pH 4 in diets was 256 to 300, 194 to 220, and 129 to 176 meq/kg in phases 1, 2, and 3 of Exp. 1, and 234 to 273, 214 to 247, and 152 to 197 meq/kg in phases 1, 2, and 3 of Exp. 2, respectively. On d 42 in Exp. 1 and d 41 in Exp. 2, one pig representing the median BW in each pen was euthanized, and digesta from the stomach, proximal jejunum, distal jejunum, and cecum were collected to analyze the properties of digesta. The pH of digesta in the stomach was 4.0, which was lower (p < 0.05) than the pH of digesta in the proximal jejunum (6.0), distal jejunum (5.9), and cecum (5.5). The pH of digesta in the cecum was lower (p < 0.05) than the pH of the digesta in the proximal and distal jejunum. The dry matter (DM) content in stomach digesta was 32.5%, which was higher (p < 0.05) than the DM content of digesta in the proximal jejunum (14.9%), distal jejunum (14.4%), and cecum (14.3%). The ABC at pH 4 of nursery diets was not correlated with the ABC at pH 3 of freeze-dried stomach digesta and pH of stomach digesta. However, the ABC-3 of freeze-dried stomach digesta was positively correlated (p < 0.05) with the DM content in stomach digesta (r = 0.57) and the pH of stomach digesta (r = 0.63) in nursery pigs. The DM content in stomach digesta was also positively correlated (p < 0.05) with the pH of stomach digesta of nursery pigs (r = 0.54). In conclusion, reducing dietary ABC by 40 to 50 meq/kg using acidifiers was not sufficient to reduce ABC or pH of stomach digesta in nursery pigs. However, the DM content in stomach digesta was positively correlated with its ABC and pH indicating that a decrease in the DM content and ABC of stomach digesta, if influenced by diets, is a primary factor contributing to reducing digesta pH in the stomach of nursery pigs.