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  • Title: Effect of limestone solubility on mineral digestibility and bone ash in nursery pigs fed diets containing graded level of inorganic phosphorus or increasing dose of a novel consensus bacterial 6-phytase variant.
    Author: Velayudhan DE, Kumar A, Marchal L, Dersjant-Li Y.
    Journal: J Anim Sci; 2022 Jun 01; 100(6):. PubMed ID: 35569061.
    Abstract:
    The effect of a novel consensus bacterial 6-phytase variant (PhyG) on total tract digestibility (ATTD) of minerals and bone ash was evaluated in pigs fed diets containing medium- and high-solubility limestone (MSL and HSL, 69.6 and 91.7% solubility, respectively, at 5 min, pH 3.0) in a randomized complete block design. For each limestone, eight diets were formulated: an inorganic phosphate-free negative control (NC) based on wheat, corn, soybean-meal, canola-meal and rice-barn [0.18% standardized total tract digestible (STTD) P and 0.59% Ca]; the NC supplemented with 250, 500, 1,000, or 2,000 FTU/kg of PhyG, and; the NC with added monocalcium phosphate (MCP) and limestone to produce three positive controls (0.33, 0.27, and 0.21% STTD P, and 0.75, 0.70, and 0.64% Ca, respectively; PC1, PC2, PC3). In total, 128 pigs (12.8 ± 1.33 kg, 8 pigs/treatment, housed individually) were adapted for 16 d followed by 4 d of fecal collection. Femurs were collected from euthanized pigs on day 21. Data were analyzed by one-way ANOVA with means separation by Tukey's test, and by factorial analysis (2 x 4: 2 levels of limestone solubility, 4 STTD P levels, and 2 × 5: 2 levels of limestone solubility, 5 PhyG dose levels). Phytase dose-response was analyzed by curve fitting. A consistent negative effect of HSL on ATTD P and Ca was observed in control diets (P < 0.001). Across phytase-supplemented diets, HSL reduced (P < 0.05) ATTD Ca and P (% and g/kg) compared with MSL. Across limestones, increasing phytase dose level increased (P < 0.05) ATTD P exponentially. Limestone solubility had no effect on bone ash, but PhyG linearly increased (P < 0.05) bone ash; 500 FTU/kg or higher maintained bone ash (g/femur) equivalent to PC1. In conclusion, ATTD P and Ca were reduced by a high compared with a medium soluble limestone, but the novel phytase improved ATTD P and Ca independent of limestone solubility. Microbial phytase is added to commercial pig diets to increase phosphorus (P) availability and reduce P excretion. It is known that an excess of calcium (Ca), mostly sourced from limestone, can affect phytase efficacy. However, less is known about the impact of limestone quality. This study investigated the effect of a medium- compared to a high-soluble limestone (MSL and HSL, respectively), in combination with increasing dose levels of a novel phytase (PhyG), on mineral digestibility and bone mineralization in young pigs. Without phytase, total tract digestibility of P was lower with HSL than MSL, indicating a negative effect of more soluble limestone on mineral digestibility. Increasing the phytase dose increased digestibility of P with either limestone, and reduced the negative effect of HSL at high dose. Bone mineralization was unaffected by limestone but markedly increased by phytase. At 1,000 FTU/kg, PhyG released an estimated 1.89 or 2.32 g/kg of digestible P from monocalcium phosphate in diets containing MSL and HSL, respectively based on bone ash content. The results demonstrate the efficacy of PhyG in young pig diets whilst indicating that limestone solubility can affect phytase efficacy.
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