Effects of particle size of yellow dent corn on physical characteristics of diets and growth performance and carcass characteristics of growing-finishing pigs.

The objectives of this experiment were to determine effects of reducing particle size on growth performance, carcass characteristics, stomach morphology, and VFA concentration in the hindgut of growing-finishing pigs if diets were formulated to a constant ME. Thirty-six gilts and 36 barrows (32.00 +/- 1.58 kg initial BW) were individually penned and randomly allotted to 4 dietary treatments in a 2 x 4 factorial design with sex (gilts and barrows) and corn particle size (i.e., 865, 677, 485, and 339 mu m) as factors. The ME was determined in the same 4 batches of corn in a previous experiment to be 3,826, 3,868, 3,895, and 3,964 kcal/kg DM, respectively. Pigs were fed a 3-phase program from 32 to 129 kg. Within each phase, 4 corn-soybean meal diets were formulated, and the only difference among diets was that the corn used was ground to the 4 specified particle sizes and soybean oil was added to the diets in decreasing amounts as the corn particle size was reduced to reflect the increased ME in corn with reduced particle size. Results of the experiment indicated that initial BW, final BW, overall ADFI, and overall ADG were not different among treatments, but final G:F for gilts decreased from 0.38 to 0.35 (linear, P < 0.05) as the particle size decreased from 865 to 339 mu m, but no difference was observed for barrows (interaction, P < 0.05). However, G: F did not change if calculated based on HCW because dressing percentage increased (linear, P < 0.01) from 79.30 to 80.29% as the particle size decreased, which was partly due to a reduction (linear, P < 0.01) from 3.01 to 2.52 kg in empty intestinal weight. Back fat depth, HCW, loin eye area, and carcass fat-free lean percentage were not different among treatments. There were no incidences of ulcers in the esophageal region of the stomach regardless of the particle size of corn, but parakeratosis in the esophageal region increased (P < 0.05) as the particle size of corn decreased. The concentration of acetate, proprionate, and butyrate in the cecal contents decreased (linear, P < 0.01) from 2,537 to 1,846, from 872 to 617, and from 702 to 226 mu g/mL, respectively, and the pH in the cecal and colon contents increased (linear, P < 0.01) from 6.04 to 6.64 and from 5.85 to 6.25, respectively, as the particle size decreased. In conclusion, by using corn ground to a smaller particle size, the amount of added fat may be reduced in the diets without affecting growth performance of barrows or carcass composition of barrows and gilts.