52 Evaluation of barley digestibility with an in vitro total tract digestion simulation

Abstract

Methods of investigating the digestibility of horse feeds have focused on the hindgut fermentation of feedstuffs, neglecting the foregut digestibility. The aim of this study was to evaluate the foregut digestibility and hindgut fermentation of barley in vitro. Three forms of barley (untreated (UB), micronised (MB)and torrefied (TB)) were evaluated. Substrates were ground to 2-mm and weighed into polyester bags (ANKOM R1020). Three replicates of 5 g (DM) per substrate were weighed into large bags (10 × 20 cm) while 4 replicates of 1g (DM) per substrate were weighed into smaller bags (4 × 10 cm). An in vitro simulated foregut digestion was set up as follows: one beaker containing artificial saliva (2.86 g/L NaCl, 1.5 g/L KHCO 3 , 2.77 g/L NaHCO 3 at pH 8.6), one with artificial gastric juice (2g/L pepsin, 1L 0.075M HCl, 10g/L Bioacidophilus powder at pH 3) and one with artificial pancreatic juice (2g/L pepsin, 1L 0.075M HCl, 85 mL/L pancreatic solution at pH 7 (45 PancrexV capsules/200 mL H 2 O)). All bags were incubated for 3h10min at 38°C: first suspended for 10min in artificial saliva, 2 h in artificial gastric juice and 1h in artificial pancreatic juice. At this point the large bags were rinsed in water and oven-dried for 24h at 60°C to determine foregut DM loss (F-DMd). Small bags were incubated for a further 72h within culture bottles with a digestion medium and equine fecal inoculum. After fermentation, suspension pH was measured, and bags oven-dried to calculate total DM loss (T-DMd). A one-way ANOVA analysis was conducted on Minitab Ⓡ 2019 to determine substrate effect on F-DMd, T-DMd and pH; significance level was set at P < 0.05 and Tukey post-hoc test used to define pairwise differences. The F-DMd was highest for TB, followed by MB, with UB being lowest ( P < 0.001), while T-DMd was highest for MB compared with UB ( P < 0.05); pH after fermentation was lower for UB in comparison with TB ( P < 0.01). These findings suggest that both micronisation and torrefaction improve the in vitro foregut digestibility of barley; however, the greatest effect was seen with torrefaction.