Benzoic acid (BA) is approved for use in fattening pig diets with an inclusion concentration of 0.5 to 1.0% with the aim to reduce ammonia emissions from slurry. It was also reported that BA supplementation resulted in small changes in blood pH. Urinary BA and hippiuric acid (HA) excretion showed relatively little diurnal variation compared with the fast consumption of dietary BA in pigs fed twice daily. The present study aimed to investigate the portal absorption profile, hepatic metabolism of BA, and renal excretion of HA underlying the relatively small impact of BA on systemic acid-base status.
A total of eight growing pigs (BW = 63 ± 1 kg at sampling) fitted with permanent indwelling catheters in the abdominal aorta, hepatic portal vein, hepatic vein, and mesenteric vein were allocated to 4 sampling blocks and randomly assigned to control (CON; nonsupplemented diet) or BA supplementation (B; control diet + 1% BA top-dressed). Feed intake was restricted to 3.6% of BW and the ration divided into 3 equally sized meals offered at 8-h intervals. Blood pH (7.465 and 7.486 ± 0.004) and urinary pH (4.99 and 7.01 ± 0.09) were less (P = 0.03 and P < 0.01) in B compared with CON. The arterial concentration, net portal flux, and net hepatic uptake of BA increased (P < 0.01) in B compared with CON. The net portal flux of BA increased (P < 0.01) after feeding with B, but remained positive (P < 0.01) at all sampling times (n = 8). Recovery of dietary BA as increased net portal flux and hepatic uptake of BA was 87 ± 5% and 89 ± 15%, respectively. The recovery of dietary BA as urinary excretion of BA and HA was 0.08 ± 0.02% and 85 ± 7%, respectively.
It is concluded that the small impact of BA supplementation on systemic acid-base status was caused by a protracted BA absorption and efficient hepatic extraction and glycine conjugation in combination with efficient renal clearance of HA. Together, these physiological mechanisms prevented major BA and HA accumulation in body fluids.
NB Kristensen, JV Nørgaard, S Wamberg, M Engbæk, JA Fernández, HD Zacho, and HD Poulsen. Absorption and metabolism of benzoic acid in growing pigs . 2009. Journal of Animal Science. 87:2815-2822. doi:10.2527/jas.2009-2003