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

This study was conducted to investigate the super dosing effects of phytase from corn-expressed phytase (CEP, 3,962 FTU/g CEP, Agrivida, Inc., Medford, MA) on metacarpal bone characteristics, apparent ileal digestibility (AID) of nutrients, and gut health of nursery pigs fed corn-soybean meal diets sufficient in P and Ca (0.44 and 0.36% STTD P and 0.83 and 0.74% Ca for Phase 1 and 2, respectively, meeting nutrient requirements suggested by NRC, 2012). Pigs (16 barrows and 16 gilts at 21 d of age with 6.2 ± 0.7 kg BW) were allotted to 4 dietary treatments (n = 8) based on a randomized complete block design with initial BW and sex blocks. Pigs were fed a basal diet supplemented with ground CEP to have phytase activities at 0, 500, 1,500, or 3,000 FTU/kg based on 2 phases (Phase 1: 10 d and Phase 2: 20 d). Analyzed phytase activities were 96, 320, 1,190, and 2,210 FTU/kg in Phase 1 diets and 60, 541, 898, 2,150 FTU/kg in Phase 2 diets, respectively. Plasma samples (d 25), metacarpal bones (d 30), ileal digesta (d 30), and tissues from jejunum (d 30) were collected. Characteristics of metacarpal bones were evaluated by determining the composition and strength. Phase 2 diets contained titanium oxide (0.25%) as indigestible external marker to calculate AID of nutrients. Numbers of proliferating enterocytes in crypts were counted in jejunum using immunohistochemistry of Ki-67. Data were analyzed using polynomial contrasts in the MIXED procedure of SAS. Increasing phytase levels increased (linear, P < 0.05) fat-free dry weight (2.02 to 2.72 g) and the amounts of P (0.17 to 0.25 g), Ca (0.36 to 0.52 g), and ash (0.15 to 18 g), and tended to increase (quadratic, P = 0.058) breaking strength (323 to 401 N at 1,500 FTU/kg) of metacarpal bones. Increasing phytase levels increased AID CP (linear, P < 0.05; 69.1 to 77.4%) and tended to increase AID ether extract (linear, P = 0.088; 54.9 to 65.7%) and AID Ca (0 vs. others, P = 0.081; 66.6 to 72.4%). Increasing phytase levels did not affect the numbers of proliferating enterocytes in crypts of jejunum. In conclusion, super dosing corn-expressed phytase up to 3,000 FTU/kg enhanced bone characteristics and nutrient digestibility of pigs fed diets with sufficient P and Ca meeting NRC requirements.