Effects of extrusion and particle size on nutrient and energy digestibility of wheat millrun in growing pigs

Particle size reduction and extrusion can increase the nutritional value of feedstuffs for pigs, but effects on wheat millrun are unclear. Thus, apparent ileal digestibility (AID) of DM, GE, CP, and AA, standardized ileal digestibility (SID) of AA and CP, and apparent total tract digestibility (ATTD) of DM and GE of coarsely or finely ground wheat millrun that was extruded or non-extruded were evaluated in pigs. Wheat millrun was ground in a hammer mill, and either extruded (X115, Wenger, Sabetha, KS) or not. Samples were ground finely (non-extruded: 283 µm; extruded: 276 µm) or coarsely (non-extruded: 508 µm; extruded: 470 µm), and mixed with 50% wheat-soybean basal diet. Six ileal-cannulated barrows (36.4 ± 0.9 kg) were fed the 4 test diets, basal diet, and N-free diet at 2.8 × maintenance DE for six 9-d periods (5 d adaptation, 2 d feces and 2 d digesta collection) in a 6 × 6 Latin square. Wheat millrun data were analyzed as 2 × 2 factorial arrangement using the MIXED model of SAS with extrusion and grinding as fixed effects, and pig and period as random effects. The 4 wheat millrun samples contained (DM basis) 18.2% CP, 13.9% ADF, and 4.6 Mcal/kg GE. Particle size and extrusion interacted (P < 0.05) for AID and SID of AA of wheat millrun. Extrusion increased (P < 0.05) the AID and SID of Lys and Ile (13–19%), and SID of Arg (6%) for coarsely, but not for finely ground wheat millrun. Coarse grinding increased (P < 0.05) AID and SID of Lys, Leu, Ile, and Arg of extruded wheat millrun (12–17%) compared with non-extruded. Extruding wheat millrun increased (P < 0.05) the AID of His (4.6%), Phe (3.9%), and Thr (6.9%); the SID of Phe (3.9%) and Thr (6.9%); the ATTD of DM (2.6%) and GE (2.4%), and DE value; and tended to increase (P < 0.10) the AID and SID of Met, compared with non-extruded. Coarsely grinding wheat millrun increased (P < 0.05) the AID of His (5.6%), Trp (11.7%), and Val (6.3%), and the SID of Trp (11.5%) and Val (6.0%) compared with finely ground wheat millrun. Extrusion increased AID of AA and ATTD of GE of wheat millrun, indicating that heat processing modified the physicochemical properties of its nutritional components making them more available to the pigs. Fine grinding decreased the nutritional value of wheat millrun.