Effects of benzoic acid and inulin on ammonia-nitrogen excretion, plasma urea levels, and the pH in faeces and urine of weaner pigs

The present experiment tested the hypothesis that dietary supplementation with BA and IN would reduce total ammonia-N (NH₃-N) excretion. Ninety-six female pigs (Large White×Landrace) aged 21±3days and weighing 5.87±0.077kg (mean±S.E.) were used in a 2×3 factorial experiment, with the respective factors being benzoic acid (BA; 0 and 5g/kg) and inulin (IN; 0, 40 and 80g/kg) in the diets. Pigs were housed individually and fed their respective diet for 3weeks. Blood samples from 6 focus pigs per diet were collected on days 14 and 21, and digesta, urine and faecal samples were collected at slaughter on day 21. Feeding only BA decreased (P=0.050) the combined faecal and urinary NH₃-N concentration while IN increased (P=0.001) the NH₃-N proportion in faeces and proportionally decreased (P=0.001) the NH₃-N proportion in urine. Additionally, dietary BA reduced the pH level in urine (P=0.001) and faeces (P=0.033), and plasma urea levels were decreased with both BA (P=0.010) and IN (P=0.008). No significant BA×IN interactions were noted. These data suggest that BA and IN can reduce NH₃-N excretion by different mechanisms, possibly by reducing excreta pH and bacterial populations (BA), as well as changing bacterial metabolic activities (BA and IN).