The inclusion of Azomite® (AZM) in broiler diets containing dicalcium phosphate has been shown to increase apparent ileal amino acid digestibility (AIAAD). These findings are likely due to die-scouring and lubrication properties that decreased the frictional heat exposure of feed. Past research indicates that modifying pellet die thickness (PDT) affects the frictional heat exposure of feed. Therefore, it was hypothesized that PDT and AZM would interact to influence AIAAD and broiler performance. The study’s objective was to determine the effect of AZM (0.0% or 0.25%) and PDT (32 and 45 mm with a common pellet diameter) on broiler performance and AIAAD from 0 to 21 days of age. Live performance did not differ due to the interaction or main effects (P > 0.05). However, AIAAD was influenced by AZM and PDT interactions (P < 0.05), with 11 amino acids demonstrating increased digestibility in the 45mm control treatment. The AIAAD increase was likely not enough to influence performance. The increased frictional heat was presumed to deactivate trypsin (TI) and chymotrypsin inhibitors (CTI), ultimately increasing AIAAD.
Quantitative analysis of TI and CTI activity, utilizing a novel assay based on the current American Oil Chemists’ Society and the American Association of Cereal Chemists International accepted procedure, showed no practically influential amount of either inhibitor before or after pelleting. The authors, therefore, speculate that the increased AIAAD was due to cell lysis of the corn aleurone layer via increased frictional heat exposure of the 45mm PDT and the absence of AZM.
