Effects of reducing the particle size of corn grain on the concentration of digestible and metabolizable energy and on the digestibility of energy and nutrients in corn grain fed to growing pigs

Two experiments were conducted to determine the apparent ileal digestibility (AID) of starch and gross energy (GE), the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA), the concentration of digestible energy (DE) and metabolizable energy (ME), and the standardized total tract digestibility (STTD) of P in corn ground to 4 different particle sizes (i.e., 865, 677, 485, and 339µm). In Experiment 1, 10 growing barrows (initial body weight: 29.2±1.4kg) were surgically equipped with a T-cannula in the distal ileum and randomly allotted to a replicated 5×5 Latin square design with 5 diets and 5 periods in each square. One lot of corn was divided into 4 batches that were ground to the specified particle sizes and each batch was used in one diet that contained 965.5g/kg corn (as-fed basis) as the only source of starch, GE, and AA. Results indicated that the AID of starch and GE was increased (linear, P<0.05) as the particle size decreased from 865 to 339μm. With the exception of Trp, there was no impact of corn particle size on the SID of CP or any indispensable AA. In Experiment 2, 40 growing barrows (initial body weight: 22.8±2.1kg) were placed in metabolism crates and allotted to a randomized complete block design with 4 diets and 10 replicate pigs per diet. Each diet contained one of the 4 batches of corn used in Experiment 1 (977.0g/kg, as-fed basis) as the only source of GE and P. Results indicated that the concentration of ME was 16.02, 16.19, 16.31, and 16.60MJ/kg dry matter for corn ground to a mean particle size of 865, 677, 485, and 339µm, respectively. The ME concentration increased (linear and quadratic, P<0.01) as the particle size decreased. The average STTD of P in the 4 batches of corn was 37.4% and no differences among treatments were observed. In conclusion, decreasing the particle size of corn from 865 to 339µm linearly increased the concentration of DE and ME and the AID of starch and GE in corn, but the particle size of corn did not affect the STTD of P or the SID of indispensable AA and CP.