Benzoic acid (BA) reduces pH of urine and thereby reduces the emission of ammonia and possibly also odorous sulphur-compounds from slurry. The effect of BA on mineral metabolism in growing pigs is not clear. The objective was therefore to study the effect of BA and methionine (Met) as a sulphur (S) source in diets for pigs on urine acidification and mineral metabolism. Twenty-four 45 kg pigs in a 2 × 2 factorial design were fed one of 4 diets, containing 0 or 2% BA and a low or high dietary S level provided through diet supplementation of 0 or 1% Met. The pigs were placed in metabolic cages for a 5 d adaptation period and a 7 d period with collection of faeces and urine. Benzoic acid was metabolized into hippuric acid which reduced urinary pH by 0.8 pH units (P < 0.001), and dietary supplementation with 1% Met reduced urinary pH by 1.0 unit (P < 0.001). The group of pigs receiving the unsupplemented diet showed the lowest apparent digestibility of phosphorus (P) (P < 0.001) and calcium (Ca) (P = 0.04). The urinary concentrations of Ca were increased (P = 0.02) by BA supplementation, but the retained proportion of absorbed P and Ca was affected by neither BA nor Met supplementation. Sulphur apparent digestibility was not (P = 0.58) affected by BA, but on the 1% Met diets, S excretion into urine was reduced (P = 0.006) by BA. In conclusion, both BA and Met supplementation increased P and Ca apparent digestibility and decreased urinary pH. The increased acid load provided through dietary BA did not significantly affect the intermediary metabolism of P and Ca.
Livestock Science, 2010, Vol 134, Issue 1-3, p. 113-115