Comparative efficacy of four commercial phytases in piglets fed an energy- and nutrient-reduced corn-wheat-soybean meal-based diet without added inorganic phosphate

Abstract

The efficacy of four commercial phytases in weaned pigs was evaluated based on mineral digestibility, bone quality, growth performance and feed costs savings. A total of 144 pigs (initial body weight 9.7 ± 1.2 kg) were assigned to six treatments [two pigs/pen, 12 pens (6 pens with males and 6 pens with females) per treatment]. Treatments comprised: a nutritionally adequate corn-wheat-based positive control containing inorganic P (PC); a negative control (NC) formulated without added inorganic phosphate, reduced in Ca, net energy and standardized ileal digestible amino acids (by 1.5 g/kg, 34 kcal/kg and up to 0.26 g/kg, respectively, vs. PC), and the NC supplemented with 1,500 FTU/kg of either: a consensus bacterial 6-phytase variant (PhyG); a Citrobacter braakii 6-phytase (PhyC); a hybrid 6-phytase (PhyH), or; an Escherichia coli phytase (PhyE). Pigs were fed ad libitum for 42 d, fecal samples were collected during d 39–41 and metacarpi/metatarsi from one pig per were extracted on d 42. Pigs fed the NC showed reduced (P < 0.05) weight gain, increased feed conversion ratio (FCR) and decreased apparent total tract digestibility (ATTD) of P, bone ash and bone strength compared with the PC. Overall (d 0–42) FCR was reduced (P < 0.05) in all phytase treatments (1.41,1.44, 1.46 and 1.49, respectively, for PhyG, PhyC, PhyH and PhyE) compared with the NC (1.71) and not significantly different from PC (1.42). The difference in overall FCR among the phytase sources was not statistically significant, P > 0.05). Compared with the NC, PhyG increased (P < 0.05) bone strength to a greater extent than the other phytases or the PC, and increased ATTD of P during d 0 to 42 compared with PhyC and PhyE. Based on ATTD P, the calculated digestible P improvement above the NC was 2.08, 1.69, 1.83 and 1.35 g/kg with PhyG, PhyC, PhyH and PhyE, respectively (P < 0.05). The PhyG-supplemented diet also showed significant production cost savings compared with the PC (−0.044 €per kg BW gain; P < 0.05) which was accompanied by reductions in both carbon footprint and nitrogen emissions. In conclusion, to a different extent, all four phytases improved growth performance, total tract P digestibility and bone strength relative to the unsupplemented NC diet but not all phytases had the same effect: PhyG had the greatest beneficial effect on P digestibility, feed efficiency, bone strength, feed cost savings, and reductions in CFP and nitrogen emissions per kg live weight.