Effect of pellet die thickness on standardized ileal digestibility of amino acids when pelleting diets fed to growing pigs

Components of the pelleting process, such as steam conditioning and feed retention time in the conditioner and die, expose feed to various degrees of heat, moisture, pressure, and shear which changes its physical and chemical characteristics. These changes may influence nutrient digestibility. Therefore, the objective of this experiment was to determine the effect of different pellet die thicknesses on the apparent ileal digestibility (<b>AID</b>) and standardized ileal digestibility (<b>SID</b>) of crude protein (<b>CP</b>) and amino acids (<b>AA</b>) in commercial diets fed to pigs. A total of 12 growing barrows with an initial average body weight of 77.1 ± 3.53 kg were allotted to a triplicated 4 × 4 Latin square design with 4 treatments and 4 periods for a total of 12 replicate pigs per treatment. The dietary treatments consisted of a mash diet and three separate diets that were pelleted using a 1-ton pellet mill equipped with different pellet die length: diameter ratios (<b>L:D</b>) of 6 (26.5- × 4.4-mm), 8 (35.2- × 4.4-mm), and 10 (44.0- × 4.4-mm). The pelleted diets were steam conditioned for 30 s (Wenger twin staff pre-conditioner, Model 150), production rate was kept constant at 708 kg per hour, and conditioning temperature was adjusted to accomplish hot pellet temperature of 85°C. Ileal cannulated pigs were housed individually in pens equipped with a feeder, a drinker, smooth-side walls, and a fully slatted metal floor. For the AID and SID of CP and AA, the diets pelleted using the L:D 8 or L:D 10 pellet dies were greater (<i>P</i> < 0.05) than the mash diet and the diet pelleted using the L:D 6 pellet die, except for Lys, Met, Trp, and Gly. Diets pelleted using an L:D 10 pellet die had increased (<i>P</i> < 0.05) SID Lys compared with the mash control with other treatments being intermediate. Diets pelleted with the L:D 8 or L:D 10 die had increased (<i>P</i> < 0.05) SID of Met compared with the mash diet, whereas there was no difference in SID of Met between the mash control and L:D 6 and L:D 8 pelleted diets. For Trp and Gly, the AID and SID of the diet pelleted using the L:D 8 pellet die were greater (<i>P</i> < 0.05) than if the L:D 6 die was used with the other treatments being intermediate. Results indicate that AA digestibility improvement resulting from pelleting diets depends on pellet die thickness with diets pelleted using an L:D of 8 or 10 having improved AA digestibility for specific AA.