Three experiments were conducted to assess enzymes with potential to improve the digestibility of dietary components by pigs fed diets based on extruded or non-extruded corn.
In Experiment 1, effects of enzyme blends (amylase, protease and xylanase) at different dose rates (high, medium, low) on the coefficient of apparent digestibility (CAD) were investigated in vitro using a two-stage enzyme incubation method.
The CAD of starch and neutral-detergent-fibre (NDF) were both higher in High and Medium enzyme diets than in Low enzyme and control diets.
Though the CAD of dry matter (DM), gross energy (GE), starch and NDF did not differ between High and Medium enzyme diets, the crude protein (CP) CAD was higher in High enzyme than in Medium enzyme diets.
Experiment 2 was designed to further examine the effects of corn extrusion, the addition of phytase and its combination with High and Medium enzyme on the CAD of dietary components.
In this experiment Medium levels of xylanase and amylase were included in both the High and Medium enzyme blends, with protease dosage being held the same in each blend as in Experiment 1.
The CAD of all dietary components evaluated was higher in the extruded corn diets.
For non-extruded corn diets, the combination of phytase with Medium and High enzymes resulted in a higher CAD of GE, CP, NDF and starch than did phytase addition alone.
In vivo experiment
In Experiment 3, both in vitro and in vivo trials were conducted to evaluate responses of corn-based diets to the extrusion process and the addition of phytase, High and Medium enzyme blends.
Five cannulated pigs were fed five diets according. Similar to the results observed in the in vitro trial, the extruded corn diet had higher CAD of DM, CP, starch, NDF and GE than the non-extruded diet.
Medium and High enzyme addition both resulted in increased DM and CP CAD of non-extruded corn diets. The CAD of amino acids in these diets with High enzyme addition was comparable with that of the extruded corn diet, and was higher than that of the non-extruded corn control diet except for Met, Thr, Trp and Cys.
These results suggest that extrusion and multiple enzyme addition are effective ways to improve the nutritional value of corn-based diets for pigs.