448 Interactive effects of extrusion and particle size reduction of corn on metabolizable energy by weanling pigs

Abstract The objective was to test the hypothesis that there are interactive effects of extrusion and reduction of the particle size of corn on apparent total tract digestibility (ATTD) of gross energy (GE) and digestible energy (DE) and metabolizable energy (ME) when fed to weanling pigs. Six corn-based diets were arranged in a 3 × 2 factorial with 3 particle sizes of corn (i.e., 700, 500, or 300 μm) and two forms (i.e., meal or extruded corn). The daily feed allowance was limited to 3.0 times the energy requirement for maintenance and pigs had free access to water. Pigs [n = 48; initial body weight (BW) = 12.8 kg; SD = 1.32) were housed in metabolism crates and allotted to the 6 diets using a randomized complete block design with two blocks. Fecal and urine samples were quantitatively collected for 4 d following 5 d of adaptation. The statistical model included diet as fixed effect and block as random effect. Contrast coefficients were used to determine effects of extrusion, linear effects of particle size, and the interaction. Results indicated that the ATTD of GE and DE and ME in corn increased by reducing the particle size of corn only if corn was in a meal form, but that was not the case for extruded corn (interaction; P < 0.001; Table 1). Regardless of particle size, the ATTD of GE and DE and ME in corn were increased (P < 0.001) by extrusion. In conclusion, reducing particle size of corn had a positive impact on energy digestibility in non-extruded corn. Regardless of particle size, extrusion of corn increased energy digestibility and DE and ME, which is likely a result of starch gelatinization in extruded corn. However, the effects of reducing particle size and extrusion were not additive, which indicates that it is not necessary to grind corn to 500 or 300 μm before extrusion.