ABSTRACT:In 2 simultaneous experiments (Exp. 1 and Exp. 2), the effects of benzoic acid (BA) and phytase (Phy) in low-P diets on bone metabolism, bone composition, and bone stability in growing and growing-finishing pigs were examined. Exp. 1 was conducted with 16 crossbred gilts in the weight range of 25 to 66 kg BW, whereas in Exp. 2, 32 crossbred gilts (25 to 108 kg BW) were used. All pigs were individually housed in pens and restrictively fed one of 4 diets throughout the experiment. Total P content of the wheat-soybean diets was 4 g/kg (all values asfed basis). The experimental diets were: 1) CC, unsupplemented control diet; 2) CBA, control diet with 0.5% BA; 3) PhyC, Phy diet with 750 Phy unit (FTU) Phy/kg and no BA; and 4) PhyBA, control diet with 750 FTU Phy/kg and 0.5% BA . Blood samples were taken at the beginning of the experiment, wk 3 (only for pigs in Exp. 1), wk 6, and before slaughter to determine P and Ca in serum and concentrations of total alkaline phosphatase (AP), serum crosslaps (SCL, marker for bone resorption), and osteocalcin (OC, marker for bone formation).Ash, P, and Ca contents of bones and bone stability were examined using the left metatarsal bones and tibia of the pigs after slaughter. Benzoic acid did not influence any of the blood variables (P > 0.09). The addition of Phy increased (P ≤ 0.03) P concentration in serum from 2.71 ± 0.08 to 3.03 ± 0.07 mmol/L at wk 3 and SCL content from 0.39 ± 0.02 to 0.45 ± 0.02 ng/mL at wk 6 and decreased (P < 0.05) OC at wk 6 by 160 ng/mL. No long-term effect of diets on serum mineral concentrations, AP, and bone markers in serum could be detected. Benzoic acid negatively affected (P ≤ 0.03) Ca content in bones and distal bone mineral density, especially in the younger pigs. In diets CBA and PhyBA, these variables were reduced by 6 and 11%, respectively. Throughout the whole growing and finishing period, Phy increased (P ≤ 0.02) ash, P, and Ca contents in bones by 29.4, 4.8, and 11.6 g/kg DM. Bone mineral density and bone mineral content were higher in diets with Phy (P ≤ 0.03), as well as breaking strength of tibia (+ 3 22%) and metatarsal bones (+ 27%; P < 0.01). The results of this study indicate that for a healthy skeleton, BA should not be used in low-P diets without the addition of Phy.

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.

In a feeding trial with 32 crossbred gilts (13-108 kg bodyweight) the effect of benzoic acid (5 g/kg diet) in low (NDF: 150 g/kg DM) and high (NDF: 202 g/kg DM) fibre diets on performance and apparent nutrient digestibility was examined. The animals were restrictively fed one of four grower and finisher diets: low fibre diet without and with benzoic acid (LF- and LF+), and a high fibre diet without and with benzoic acid (HF- and HF+). At 56 kg bodyweight, four animals per diet were slaughtered to obtain data on volatile fatty acid (VFA) production in the gut. In the grower period, digestibility of nitrogen, energy and neutral detergent fibre was positively influenced by benzoic acid (p < 0.01) and reduced by fibre addition (p < 0.01). The concentration of butyric acid in caecum and colon was increased by benzoic acid (p < 0.05). Dietary fibre content did not influence VFA concentrations. It is concluded that the addition of benzoic acid helped animals to utilise high fibre diets better.

No abstract

No abstract