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The use of filter bags in combination with an in vitro system to evaluate forage degradation in mixed substrates

Castro-Montoya, J.M., Dickhoefer, U.
Animal feed science and technology 2019 v.249 pp. 46-53
acetone, bags, corn silage, fatty acid composition, fermentation, forage, grass hay, short chain fatty acids
The current study determined the effects of using ANKOM R510 filter bags for substrate incubation during in vitro fermentations using the ANKOM RF technique on gas production (GP, ml/g DM), truly degraded dry matter (TDDM, g/100 g), and total short chain fatty acids concentration (SCFA, μmol/ml). Maize silage and grass hay tested separately in combination with a concentrate mixture (70:30 ratio, dry matter basis) were used as substrate for three experiments. In Experiment 1, 2.0 g of substrate (1.4 g of forage and 0.6 g of concentrate) were incubated during 48 h following three methodologies: Control, where the forage and concentrate were incubated freely in the incubation medium; Forage.In, where the forage was incubated inside the filter bag while the concentrate was incubated freely in the medium; Conc.In, where the concentrate was incubated inside the bag while the forage was incubated freely in the medium. In Experiment 2a only the Control and the Conc.In methodologies were considered. The sample size was reduced to 1.2 g and the incubation time was 24 h. A further modification was included in Experiment 2b by pre-washing the filter bags with acetone prior to the incubation and otherwise following the same procedures of Experiment 2a. A regression of GP, TDDM and SCFA of the control on those parameters of the Conc.In across all three experiments was performed to evaluate the correspondence between both methodologies. In Experiment 1 GP, total SCFA and TDDM decreased when utilizing the filter bag, particularly for the Forage.In methodology (P < 0.08), likely by interfering with fiber degradation. Reducing the sample size (Experiment 2a) minimized the differences between the Control and Conc.In compared with Experiment 1 (P = 0.03). No further improvement was obtained by pre-washing the bags prior to the incubation (Experiment 2b). A high correlation (R2 > 0.90) between control and Conc.In was observed for all three parameters, indicating that comparable results can be expected when the concentrate is incubated inside the filter bag to those obtained when the mixed substrate is incubated freely in the incubation medium. Overall, the use of R510 filter bags to separately incubate the forage and the concentrate portion of a substrate can be used with confidence as long as the concentrate portion is incubated inside the bag and all samples studied are evaluated using the same methodology.