Effect of xylanase supplementation of a phytase-supplemented diet on apparent total tract digestibility in pigs

Dietary xylanase (endo-1,4-β xylanase [Enzyme Commission number 3.2.1.8]) supplementation can improve energy digestibility in pigs; however, the effect of supplementation to a diet already containing phytase has not been clearly determined. A total of 25 barrows (76.5 ± 0.6 kg start weight) were allotted to 5 treatments to evaluate xylanase as follows: 1) a positive control (PC), a corn–soybean meal–based diet with 15% each of corn germ meal, corn dried distillers’ grains with solubles, and wheat middlings; 2) a negative control (NC), in which ME was reduced by 103 kcal/kg from the PC diet by fat replacement with starch; 3) NC + 8,000 xylanase units (BXU)/kg diet (NX1); 4) NC + 16,000 BXU/kg diet (NX2); and 5) NC + 24,000 BXU/kg diet (NX3). All diets were formulated to contain 250 phytase units of phytase/ kg diet. Feces and urine were collected for 5 consecu tive days after a 7-d adaptation period for determining apparent total tract digestibility (ATTD) and retention. There were no differences in ATTD of DM, GE, N, ADF, and P. However, the PC treatment had the greatest ATTD of ether extract (P < 0.05) among all groups. Energy retention in the PC treatment tended to be greater than that in the NC, NX1, and NX2 treatments but similar to that in the NX3 treatment (P = 0.09). In the comparison of xylanase effects, ATTD of hemicellulose linearly increased with increasing xylanase level (P < 0.05); a tendency for improvement in ATTD of NDF was observed at the 24,000 BXU/ kg level (linear, P = 0.15). These results demonstrate that xylanase supplementation to a high-fiber diet (19.8% NDF) also containing phytase can improve hemicellulose and perhaps NDF and digestibility and, thereby, energy utilization.