PSVIII-18 - Standardized amino acid digestibility and nitrogen-corrected true metabolizable energy of frozen raw, freeze-dried raw, fresh, and extruded dog foods using cecectomized and conventional rooster assays

Abstract: Processing conditions, particularly temperature and duration of heating, impact the digestibility of pet foods. Various alternative commercial pet food formats are now available, but few have been well tested. Therefore, the objective of this study was to determine the amino acid (AA) digestibility and nitrogen-corrected true metabolizable energy (TMEn) of frozen raw, freeze-dried raw, fresh, and extruded dog foods using the precision-fed cecectomized and conventional rooster assays. The diets tested were: Chicken and Barley Recipe [extruded diet; Hill’s Science Diet (EXT)], Chicken and White Rice Recipe [fresh diet; Just Food for Dogs (FRSH], Chicken Formula [raw frozen diet; Primal (FRZN)], Chicken and Sorghum Hybrid Freeze-dried Formula [hybrid freeze-dried raw diet; Primal (HFD)], and Chicken Dinner Patties [raw freeze-dried diet; Stella & Chewy (FD)]. Two precision-fed rooster assays utilizing Single Comb White Leghorn roosters (1.5-2.5 years, 2.5-3kg) were conducted. In the first assay, 20 cecectomized roosters (n=4) were used to determine AA digestibility. In the second assay, 20 conventional roosters (n=4) were used to determine TMEn. In both assays, roosters were crop intubated with 12 g of test diet and 12 g of corn, and then excreta was collected for 48 h. The reactive lysine:total lysine ratios were 0.94, 0.96, 0.93, 0.93, and 0.95 for the EXT, FRSH, FRZN, HFD, and FD diets, respectively. In general, FD had the highest AA digestibilities and EXT had lowest AA digestibilities. Arginine digestibilities were different (P< 0.05) across all diets and in this pattern: FD > FRZN > FRSH > HFD > EXT. Isoleucine digestibilities were different (P< 0.05) across all diets, but with a slightly different pattern: FD > FRZN > FRSH > EXT > HFD. Lysine digestibility was higher (P< 0.05) in FD and FRZN than EXT, with other diets being intermediate. Methionine digestibility was higher (P< 0.05) in FD than FRSH, with other diets being intermediate. Threonine digestibility was higher (P< 0.05) in FD than EXT, with other diets being intermediate. Valine digestibilities were different (P< 0.05) across all diets and in this pattern: FD > FRZN > EXT > FRSH > HFD. Digestibilities of the other essential AA were not different among diets. TMEn was higher (P< 0.05) in FRZN than FD, FRSH, and EXT, higher (P< 0.05) in HFD than FRSH and EXT, and higher (P< 0.05) in FD than EXT. In conclusion, our results support the notion that diet processing impacts AA digestibility, with freeze-dried raw, frozen raw, and fresh diets consistently having higher digestibility coefficients, not to mention a greater TMEn, than the extruded diet. More research in dogs is necessary to test the effects of these diet formats on palatability, digestibility, stool quality, and other physiologically relevant outcomes.