Proc. Soc. Nutr. Physiol. (2008) 17
57. Effect of benzoic acid on urinary mineral excretion in growing pigs (Wirkung von Bezoesäure auf die Mineralstoffausscheidung über der Harn beim wachsenden Schwein). H.D. Hess* and A.
Gutzwiller – Posieux
Organic acids, such as benzoic acid (BA), have antimicrobial activity, may improve growth performance in pigs and lower urinary pH. However, a reduced urinary pH could also result in an elevated urinary excretion of minerals. This would be particularly relevant in diets with reduced phosphorus (P) contents which are frequently used in European pig production systems in order to lower P losses to the environment. Results of a recent experiment indicated that diets with reduced P contents (4 g/kg) may impair mineralization and breaking strength of bones in pigs and that this effect tended to be enhanced by dietary BA supply (1). The aim of this study was to test whether BA combined with normal or reduced dietary P levels affects urinary mineral excretion in growing pigs.
Methods: 16 barrows with an initial body weight (BW) of 24.6±2.3 kg were assigned according to litter origin and BW to 4 experimental diets: normal P (NP; 5.7 g/kg) supplemented with 0 or 1% BA and low P (LP; 4.0 g/kg) supplemented with 0 or 1% BA. All 4 diets had a Ca:P ratio of 1.3:1, contained 13.6 MJ/kg digestible energy and the crude protein content was 163 and 150 g/kg in NP and LP diets, respectively. At 50 kg BW, the barrows were placed in metabolic cages for 4 consecutive days for measurement of feed intake and total collection of urine and feces. Data were subjected to analysis of variance regarding the 2×2 factorial arrangement of treatments. Litter origin, P content (P), BA and the interaction between P×BA were considered as sources of variation.
Results: Irrespective of dietary P content, dietary BA supply decreased (P<0.05) urinary pH by 0.7 units on average (Table 1). As intended intake of Ca and P was lower (P<0.001) in barrows fed LP diets and was not affected by BA supply (P>0.2). Urinary excretion of Ca (P<0.1) and P (P<0.05) increased with the addition of BA. Urinary Mg excretion was increased when BA was combined with reduced but not with normal P (P×BA interaction; P<0.01). Fecal Ca, P and Mg excretion was decreased (P<0.001) when LP diets were offered but was not affected (P>0.1) by BA (data not shown). Neither dietary P content nor BA affected (P>0.1) Ca, P or Mg retention (data not shown).
Table 1 Urinary pH, intake and urinary excretion of minerals (g/d) in growing pigs (n=4)
P content Normal Low SEM P-values
Benzoic acid 0% 1% 0% 1% P BA P×BA
Urinary pH 6.71 5.97 6.21 5.57 0.258 0.109 0.021 0.847
Intake
Ca 13.5 13.9 10.1 9.9 0.35 <0.001 0.843 0.362
P 10.1 10.3 7.2 7.5 0.25 <0.001 0.285 0.866
Mg 2.5 2.5 1.8 1.9 0.06 <0.001 0.290 0.470
Urinary excretion
Ca 0.10 0.13 0.08 0.24 0.052 0.390 0.078 0.211
P 0.49 0.55 0.44 1.04 0.125 0.108 0.022 0.051
Mg 0.08 0.08 0.15 0.47 0.039 <0.001 0.002 0.002
Conclusion: The results of this study revealed that the addition of benzoic acid to the diet of growing pigs increases urinary Ca, P and Mg excretion, particularly when combined with a reduced dietary P content. However, the contribution of urinary excretion to total mineral excretion was too small to affect Ca, P or Mg retention.
1) GUTZWILLER, A, HESS, HD, STOLL, P, LIESEGANG, A and GUGGISBERG D, (2007):
Schriftenreihe Institut für Nutztierwissenschaften, ETH Zurich, Band 29, 201-203.
* Agroscope Liebefeld-Posieux Research Station ALP, P.O. Box 64, CH-1725 Posieux
