PSVI-6 - Benzoic acid supplementation in low protein nursery diets for pigs

Abstract: Using low crude protein (CP) diets can be an alternative to reduce feed costs and nitrogen waste in swine production. However, low CP diets could limit nitrogen available for non-essential amino acid, and particularly glycine, production. The objective of this study was to evaluate the effect of adding benzoic acid, which is excreted in urine as its glycine conjugate hippuric acid, to low CP diets on growth performance of starter pigs. At 28 d age, pigs were weaned and divided into nursery room pens according to body weight and sex (5 mixed-sex pigs per pen). Pigs were fed a commercial nursery diet for 4 d; at 32 d age, pigs were weighed and pens were assigned to one of three dietary treatments: 1) high crude protein (HCP; 19.8% CP; n = 12 pens); 2) low crude protein (LCP; 15.8% CP; n = 11 pens) and 3) low crude protein + benzoic acid (LCP+BA; 15.8% CP, 0.9% benzoic acid; n = 12 pens). Pigs were fed for four weeks and pig body weights and feed disappearance were measured weekly to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency (FE; gain-to-feed ratio). At day 0, 14 and 28, blood was collected from one pig/pen by jugular venipuncture. Serum was analyzed for hippuric acid and amino acid concentrations. The ADG of HCP group (0.58 ± 0.01 kg/d) was greater than LCP (0.54 ± 0.01 kg/d) and LCP+BA (0.50 ± 0.01 kg/d; P < 0.05); ADG of LCP was also greater than LCP+BA (P < 0.05). There was no difference in ADFI among groups (P > 0.05). However, FE of LCP+BA was lower than both HCP (0.536 vs 0.579 ± 0.006 kg/kg; P < 0.05) and LCP (0.536 vs 0.576 ± 0.006 kg/kg; P < 0.05); there was no difference in FE between HCP and LCP (P > 0.10). Serum hippuric acid concentration was greater in the LCP+BA group compared to either the HCP and LCP groups on day 14 and day 28 (P < 0.05). Glycine concentration in LCP+BA (518 ± 33 µmol/L) was lower than LCP (637 ± 33 µmol/L; P < 0.05), whereas glycine concentration of HCP (584 ± 33 µmol/L) was intermediate. Lysine concentrations were lowest in HCP (106 ± 8 µmol/L), intermediate in LCP (139 ± 8 µmol/L), and greatest in LCP+BA (168 ± 8 µmol/L; P < 0.01). The decrease in growth performance caused by benzoic acid is greater than what occurs with low CP diets alone. Higher lysine levels in pigs fed with benzoic acid suggest that lysine was not used as efficiently for growth. Collectively, supplementing benzoic acid to nursery diets without also including additional protein could be problematic.