Dose-response effect of a consensus bacterial 6-phytase variant on mineral digestibility and retention in weaned pigs fed European-style diets with varying phytate-phosphorus content

Abstract

The effect of increasing dose levels of a consensus bacterial 6-phytase variant (PhyG) on the digestibility and retention of minerals, bone ash and growth performance was evaluated in weaned pigs fed a mixed cereals diet containing varying levels of phytate-phosphorus (PP) and no added phosphate. Treatments comprised: a wheat, corn, barley and soybean meal-based negative control diet (NC), containing no inorganic phosphate and reduced in calcium (Ca), energy and digestible amino acids formulated at three PP levels (low, 2.40 g/kg; medium, 2.90 g/kg; high, 3.40 g/kg diet), and; the NC supplemented with PhyG at 500, 1000, 2000 or 4000 phytase units (FTU)/kg or with a comparator phytase (PhyB) at 1000 FTU/kg. A completely randomized design employed 144 DanBred $\times$ Piétrain males with 8 pigs per treatment; initial body weight (BW) = 9.2 ± 1.0 kg. Pigs were adapted for 10 days in floor pens (2 animals per pen) and 5 days in metabolism crates (individually), followed by 5 days of fecal collection. Pigs were slaughtered on day 20 to collect ileal digesta and femurs. Dietary PP level had no effect on BW, BW gain, feed intake or apparent ileal digestibility (AID) coefficients of P or Ca, bone ash or strength. Apparent total tract digestibility (ATTD) and retention coefficients of P at day 20 were reduced in medium compared with low PP diets (-6.4 % and −6.6 %, respectively; P < 0.05) whereas ATTD and retention of Ca were reduced in medium or high compared with low PP diets (P < 0.05). Body weight (day 10 and 20), day 0–20 BW gain, AID of P, ATTD and retention of P and Ca and ATTD of gross energy increased exponentially with increasing PhyG dose level (P < 0.05) across PP levels; compared with the NC, PhyG at 1000 FTU/kg increased ATTD, standardized total tract digestibility (STTD) and retention of P from 0.438 to 0.634, 0.609–0.679 and 0.433–0.629, respectively, whereas at 4000 FTU/kg these measures were increased to 0.683, 0.678 and 0.676, respectively. At 1000 FTU/kg, ATTD and retention of P and Ca were higher with PhyG than PhyB (ATTD of P 0.634 compared with 0.608). In conclusion, in a European-style diet, PhyG increased total tract digestibility and retention of minerals in weaned pigs in diets of varied PP level, and at 1000 FTU/kg PhyG was more efficacious at improving ATTD of P than PhyB. Negative effects of increasing PP level on ATTD of P and Ca were ameliorated by increasing the dose level of the phytase.