Super Dosing Effects of Corn-Expressed Phytase on Growth Performance, Bone Characteristics, and Nutrient Digestibility in Nursery Pigs Fed Diets Deficient in Phosphorus and Calcium

This study was conducted to determine the super dosing effects of phytase from corn-expressed phytase (CEP, Agrivida, Inc., Medford, MA) on growth performance, metacarpal bone characteristics, and apparent ileal digestibility (AID) of nutrients in nursery pigs fed corn-soybean meal diets deficient in P and Ca. Seventy pigs (21 d of age with 6.7 ± 0.6 kg BW) were individually housed and allotted to 7 treatments in a randomized complete block design with initial BW and sex blocks. A negative control diet (NC) had 0.40% ATTD P and 0.80% Ca without supplemental phytase. Other 6 treatment diets had 0.25% ATTD P and 0.68% Ca supplemented with phytase at 0, 500, 1,000, 2,000, 4,000, and 6,000 FTU/kg diet. Pigs were fed for 30 d (Phase 1: 10 d and Phase 2: 20 d) with ad libitum access to water and diets. Feed intake and BW were recorded every 10 d. Pigs were euthanized on d 30 to collect metacarpal bones and ileal digesta. Data were analyzed using polynomial contrasts in the MIXED procedure of SAS. Pigs fed NC had greater (P < 0.05) ADG, G:F, bone P (g and %), AID P, and bone strength than pigs fed a basal diet without phytase. Increasing phytase levels increased (linear, P < 0.05) BW (13.5 to 18.0 kg), ADG (230 to 370 g/d), ADFI (420 to 520 g/d), and G:F (0.54 to 0.73). Increasing phytase levels increased (linear, P < 0.05) weight (5.85 to 7.22 g), fat-free dry weight (1.19 to 1.73 g), the amounts of P (0.10 to 0.16 g) and ash (0.10 to 0.13 g), and breaking strength (242 to 408 N) of metacarpal bones. Increasing phytase levels increased (linear, P < 0.05) AID P (78.1 to 86.1%), AID DM (53.0 to 79.4%), AID GE (50.3 to 78.6%), and AID ether extract (59.8 to 75.5%). Pigs fed basal diets had smaller (P < 0.05) ADG, ADFI, bone P (g and %), and AID P than NC with phytase below 4,000 FTU/kg, whereas they did not differ (P > 0.10) from NC with phytase above 4,000 FTU/kg. In conclusion, super dosing CEP up to 6,000 FTU/kg improved growth performance, bone characteristics, and nutrient digestibility in pigs fed P and Ca deficient diets. Pigs fed P and Ca deficient diets supplemented with phytase above 4,000 FTU/kg performed similar to pigs fed a diet with sufficient P and Ca.