Effects of feeding corn-expressed phytase on the live performance, bone characteristics, and phosphorus digestibility of nursery pigs.

A 41-d feeding trial was conducted to determine the efficacy of a corn-expressed phytase (GZ; GraINzyme, Agrivida Inc., Woburn, MA) on the live performance, bone characteristics, and P digestibility of nursery pigs fed a reduced P diet. Weaned piglets (21 ± 3 d; n = 324) were acclimated on a common diet for 7 d (phase 1) before randomization into 54 single-sex pens (5 gilt and 4 barrow pens per treatment) containing 6 pigs (6.6 ± 1.2 kg) per pen. Six treatments were fed: positive control (PC; 0.4% or 0.32% aP for phase 2 or 3 and 4, respectively), negative control (NC; 0.15% reduction in aP), and 500, 1,000, 2,000, or 4,000 FTU per kg phytase from GZ added to NC in a 3-phase feeding program. Pigs were weighed on day 1, 14, 28, and 41, and feed disappearance recorded per phase. Apparent total tract digestibility (ATTD) of P was determined by feeding chromic oxide marker (day 28 to 35) and collecting fecal samples on day 35. On day 41, 4 pigs per pen were euthanized and metacarpal bones were collected to evaluate bone breaking strength (BBS) and ash. Data were analyzed using PROC GLM of SAS (block, sex, and treatment). Treatment least squares means were separated and linear and quadratic treatment effects evaluated. Other than feed efficiency (G:F) and day 15 to 28 ADFI, the pigs fed PC were superior (P < 0.05) to NC-fed pigs in all other variables. Pigs fed ≥500 FTU per kg phytase had increased (P < 0.05) ADG and ADFI compared to NC pigs and equivalent (P > 0.05) ADG and ADFI as PC pigs from day 0 to 41. Feeding ≥500 FTU per kg phytase resulted in higher (P < 0.05) ATTD of P than both NC and PC pigs and higher (P < 0.05) BBS and bone ash weight than NC. Pigs fed 1,000 or 2,000 FTU per kg phytase had equivalent (P > 0.05) BBS and bone ash weight compared to pigs fed PC diets. Feeding 4,000 FTU per kg phytase resulted in higher (P < 0.05) day 1 to 41 ADG, ATTD of P, and bone ash weight compared to feeding ≤1,000 FTU per kg phytase or PC diets. There were linear (P < 0.05) increases in ADG, ADFI, ATTD of P, BBS, and bone ash characteristics as GZ inclusion increased. In conclusion, ≥500 FTU per kg phytase from GZ improved growth, ATTD of P, BBS, and bone ash when added to a reduced P diet and 4,000 FTU per kg phytase increased growth greater than the PC treatment.