Influence of benzoic acid and phytase in low-phosphorus diets on bone characteristics in growing-finishing pigs1

Abstract

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.

Mineralisation of tubular bones is affected differently by low phosphorus supply in growing‐finishing pigs

“…Generally, the observed low bone net mineralisation in pigs fed the LP diet is in agreement with other studies confirming that deficient P supply leads to reduced mineral content of bones …”

“…Similar to previous reports, the present results showed that the LP supply was not sufficient to achieve the same overall BMD level in the diaphysis of all four studied bones as the MP and HP supplies. This is supported by previous results showing that decreased P supply to pigs reduced body P retention .…”

“…Generally, the observed low bone net mineralisation in pigs fed the LP diet is in agreement with other studies confirming that deficient P supply leads to reduced mineral content of bones. 9,10,13,14,25-27 wileyonlinelibrary.com/jsfa Similar to previous reports, 13,25 the present results showed that the LP supply was not sufficient to achieve the same overall BMD level in the diaphysis of all four studied bones as the MP and HP supplies. This is supported by previous results showing that decreased P supply to pigs reduced body P retention.…”

“…In the present study, an LP‐induced lower trabecular BMD was solely found in the distal section of the metacarpal, which indicates that the distal trabecular tissue is more involved in bone mineral metabolism than the proximal part. Buhler et al found a similar reduction in the trabecular BMD in pigs weighing 66 kg when dietary P decreased even though the difference was counterbalanced at 108 kg BW (1.4 versus 2.6 g digestible P kg −1 ). Moreover, Larsen et al found that low dietary Ca (3.5 versus 9.4 g kg −1 DM) resulted in a 36% lower trabecular bone volume and increased osteoid thickness.…”

Effects of Benzoic Acid and Dietary Calcium:Phosphorus Ratio on Performance and Mineral Metabolism of Weanling Pigs

“…The effects of BA on bone traits of growing-finishing pigs reported by Bühler et al (2010) are equivocal: Benzoic acid tended to reduce ash concentration in the metatarsal bones, but did not affect the breaking strength of the tibia, despite a significantly reduced tibial bone mineral density. In conclusion, the majority of published data do not show significant negative effects of BA on bone breaking strength and bone ash concentration, suggesting that the risk of reduced bone mineralization caused by this feed additive is low.…”