Comparative effects of benzoic acid and sodium benzoate in diets for nursery pigs on growth performance and acidification of digesta and urine.

The objective of this study was to evaluate the comparative effects of benzoic acid and sodium benzoate in feeds on digesta pH, urinary pH, and growth performance for nursery pigs. A total of 432 pigs (6.9 ± 0.9 kg BW) were assigned to eight treatments (6 pigs per pen, replication = 9) in a randomized complete block design with initial body weight (BW) as a block and fed for 41 d in three phases (7/17/17 d, respectively). Treatments were 1) a basal diet (NC), 2) NC + 0.25% bacitracin methylene disalicylate (antibiotic; bacitracin: 250 g/t feed; PC), 3) NC + 0.25% benzoic acid, 4) NC + 0.35% benzoic acid, 5) NC + 0.50% benzoic acid, 6) NC + 0.30% sodium benzoate, 7) NC + 0.40% sodium benzoate, and 8) NC + 0.60% sodium benzoate. Growth performance and fecal scores were measured for each phase. One gilt representing the median BW of each pen was euthanized to collect digesta from the stomach, proximal jejunum, distal jejunum, and cecum, and urine. The PC tended to improve average daily gain (ADG) in phase 1 (P = 0.052) and phase 2 (P = 0.093) as well as average daily feed intake (ADFI) in phase 2 (P = 0.052). Overall, increasing supplemental benzoic acid tended to have a quadratic effect on ADG (P = 0.094), but no difference in ADFI was observed. Increasing supplemental sodium benzoate showed a quadratic effect (P < 0.05) on ADG and linearly increased (P < 0.05) ADFI. Urinary pH linearly decreased (P < 0.05) with increasing supplemental benzoic acid, but was not affected by supplemental sodium benzoate. Increasing supplemental benzoic acid or sodium benzoate linearly increased (P < 0.05) benzoic acid content in digesta of the stomach. Increasing supplemental benzoic acid or sodium benzoate also linearly increased (P < 0.05) urinary hippuric acid. However, the PC did not decrease urinary pH or increase urinary benzoic acid and hippuric acid. With slope-ratio assay using ADG and urinary hippuric acid as dependent variables and benzoic acid intake as an independent variable, the relative bioavailability of benzoic acid compared to sodium benzoate was not different. In conclusion, supplementation of benzoic acid and sodium benzoate could improve the growth performance of nursery pigs. The relative bioavailability of sodium benzoate to benzoic acid of nursery pigs did not differ based on BW gain and urinary hippuric acid.