Effects of dietary β-mannanase supplementation on the additivity of true metabolizable energy values for broiler diets

OBJECTIVE: This experiment was conducted to determine the effects of dietary β-mannanase on the additivity of true metabolizable energy (TME) and nitrogen-corrected true metabolizable energy (TME(n)) for broiler diets. METHODS: A total of 144 21-day-old broilers were randomly allotted to 12 dietary treatments with 6 replicates. Five treatments consisted of 5 ingredients of corn, wheat, soybean meal, corn distillers dried grains with solubles, or corn gluten meal. One mixed diet containing 200 g/kg of those 5 ingredients also was prepared. Additional 6 treatments were prepared by mixing 0.5 g/kg dietary β-mannanase with those 5 ingredients and the mixed diet. Based on a precision-fed chicken assay, TME and TME(n) values for 5 ingredients and the mixed diet as affected by dietary β-mannanase were determined. RESULTS: Results indicated that when β-mannanase was not added to the diet, measured TME and TME(n) values for the diet did not differ from the predicted values for the diet, which validated the additivity. However, for the diet containing β-mannanase, measured TME(n) value was greater (p<0.05) than predicted TME(n) value, indicating that the additivity was not validated. CONCLUSION: In conclusion, the additivity of energy values for the mixed diet may not be guaranteed if the diet contains β-mannanase.