Pellet die thickness and a commercial throughput agent interacted to demonstrate that high frictional heat increased apparent ileal amino acid digestibility, but did not influence trypsin inhibitor activity or male broiler performance

Modifying pellet die thickness (PDT) has been shown to affect the frictional heat exposure of feed. The inclusion of Azomite (AZM) in broiler diets containing dicalcium phosphate has been shown to maintain apparent ileal amino acid digestibility (AIAAD). This is likely due to AZM's proposed die-scouring and lubrication properties that decreased the frictional heat exposure of feed which can change protein conformation and reduce AIAAD. Therefore, it was hypothesized that PDT and AZM would interact to influence AIAAD and broiler performance. The objective of the study was to determine the effect of AZM (0.0% or 0.25%) and PDT (32 and 45 mm; with a constant pellet diameter of 4.5 mm) on broiler performance and AIAAD from 0 to 21 d of age using a corn and soybean meal-based diet. Live performance was not influenced by AZM, PDT, or their 2-way interaction (P > 0.05). However, AIAAD was affected by AZM and PDT interactions (P < 0.05), with 11 amino acids demonstrating increased AIAAD in only the 45 mm control treatment. The AIAAD increase was likely not enough to influence performance. It was presumed that increased frictional heat deactivated trypsin inhibitors (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 (Ba 12–75) and the American Association of Cereal Chemists International (22-40.01) accepted procedures, showed no practically influential amount of either inhibitor before or after pelleting. The authors, therefore, speculate that the increased AIAAD was due to corn aleurone layer cell wall lysis via increased frictional heat exposure of the 45 mm PDT and the absence of AZM.