LAUSR

Previous work has evaluated fermentation of fiber ingredients; however, the effect of extrusion has rarely been explored. The objective was to determine post-extrusion fiber fermentability with a dog fecal in vitro model. Dietary treatments containing 10% apple pomace (AP), blueberry pomace (BP), or miscanthus grass (MM) were compared to a control (CD) with no added fiber. Diets were produced with a single screw extruder under set processing conditions. In addition, higher (MH) and lower (ML) mechanical energy was applied to miscanthus treatments. Post-extrusion samples were pre-digested and residual fibers fermented for 1, 3, 6, and 12-hours. Short chain fatty acids (SCFA) and organic matter disappearance (OMD) were determined for each fiber and time point. Data were analyzed as a completely randomized design with statistical software (SAS, v 9.4). The OMD was greatest (P < 0.05; 56.1%) for CD than AP, MM, and BP (average 35.19%). Total SCFA concentration was greatest (P < 0.05) for CD followed by AP and BP, and lowest for MM (1.53, average 1.19, and 0.92 mmol*g-1 of substrate, respectively). Acetate proportions were highest (P < 0.05) for BP (60.85%) and lowest for CD (52.86%), with AP and MM intermediate (average 56.57%). Propionate proportions were similar (P < 0.05) across all treatments (average 21.18%). Butyrate proportions were highest (P < 0.05) for CD (11.91%) and lowest for BP and MM (average 9.60%), with AP similar (10.15%) to all treatments. Processing did not affect (P < 0.05) OMD, SCFA concentration or proportions among the different mechanical energy inputs to the miscanthus grass treatments. When corrected for total fiber, CD had the lowest SCFA concentration (P < 0.05; 6.74 mmol*100g-1of diet) compared to all other treatments (average 12.8 mmol*100g-1of diet). While, CD was most fermentable on a gram of fiber basis; on a dietary basis, all fiber treatments had greater concentrations of total SCFA and butyrate.