Influence of benzoic acid and dietary protein level on performance, nitrogen metabolism and urinary pH in growing-finishing pigs

An experiment was conducted to examine the effect of benzoic acid and two dietary protein levels on pig performance, nitrogen balance and urinary pH. A total of 24 crossbred barrows (26 kg to 106 kg BW) received one of four diets: low protein level with and without 1% benzoic acid (LP- and LP+, respectively) and high protein level with and without 1% benzoic acid (HP- and HP+, respectively). The animals were fed restrictively grower and finisher diets and were kept in metabolic cages in weeks 3, 6, 9, and 12 of the experiment. The addition of benzoic acid did not improve weight gain and feed conversion ratio. N-intake and digested N were only influenced by dietary protein level (p < 0.01), while N-balance was similar in all four diets. Dietary benzoic acid improved N-digestibility in the grower period (p < 0.01) but not in the finisher period. The addition of benzoic acid reduced urinary pH by about one pH-unit in both feeding periods independent of the protein level of the diet (p < 0.01) and increased the concentration of urinary hippuric acid markedly (p < 0.01). The results of this study indicate a positive influence of dietary benzoic acid on pigs especially in case of feeding a low protein diet in the grower period.