Effect of the pelleting process on diet formulations with varying levels of crystalline amino acids and reducing sugars on digestibility in growing pigs

The objective of this experiment was to determine the effects of pelleting on the standardized ileal digestibility (SID) of amino acids (AA) and crude protein (CP) in diets with or without increased concentrations of free AA and reducing sugars (RS). Eight individually housed, ileal cannulated barrows (initially 31.4 kg) were allotted to an 8 × 8 Latin square with eight diets and eight 7-d periods with ileal digesta collected on days 6 and 7. Treatments were arranged in a 2 × 2 × 2 factorial with the main effects of diet form (mash or pellet), crystalline AA (low or high), or RS (low or high), provided by distillers dried grains with solubles and bakery meal. Diets were pelleted to achieve a hot pellet temperature of 85 to 88 °C. Data were analyzed as a Latin square design using the GLIMMIX procedure of SAS 9.4. A feed form × RS interaction (P < 0.026) for SID of tryptophan was observed. Feeding pelleted low RS diets increased SID of tryptophan compared with mash high and low RS diets, and pelleted high RS diets. For the main effects of feed form, the SID of total AA, CP, and indispensable AA was greater (P < 0.042) in pelleted diets compared with mash diets. For the main effects of crystalline AA, pigs fed high crystalline AA had increased (P = 0.007) SID of tryptophan and decreased (P = 0.050) SID of histidine compared with those fed low crystalline AA diets. For the main effects of RS, high RS diets had decreased (P < 0.05) SID of total AA, CP, and indispensable AA compared with low RS diets. In conclusion, pelleting diets increased AA digestibility, and pelleting diets with increased crystalline AA or RS did not affect the improvement in AA digestibility from pelleting. Diets formulated with high crystalline AA had increased SID of tryptophan. Formulating diets with high RS resulted in decreased AA digestibility compared with corn-soybean meal-based diets.