Effect of in vitro techniques and exogenous feed enzymes on feed digestion

• Several factors associated with batch culture affected in vitro fermentation.
• Manual vs. automated gas recording resulted in reduction of dry matter digestibility (DMD).
• Exogenous enzyme effect on DMD was independent on the factors studied.

The objective of this study was to assess whether changing gas production (GP) recording method (GPR), substrate delivery method (MD), and fineness of substrate grinding (FG) alter in vitro GP from feed digestion with and without exogenous feed enzymes (EFE) treatment. The experiment was a 2 GPR × 2 MD × 2 FG × 2 EFE factorial arrangement using barley straw, alfalfa hay or wheat dried distillers grain with solubles (DDGS) as substrates. There was no interaction of EFE with GPR, MD or FG on GP and dry matter digestibility (DMD). Compared to automated methods, manual recording increased (P < 0.01) GP, but enclosing substrate in bags vs. dispersing it in media reduced (P < 0.04) GP from both alfalfa hay and DDGS. Gas production was greater (P < 0.05) with 2 mm vs. 1 mm ground barley straw. The manual vs. automated GP recording resulted in reduced (P < 0.01) DMD of alfalfa hay and wheat DDGS. For all three substrates, DMD was consistently higher (P < 0.01) when enclosed in bags vs. dispersed in bottles. The DMD of alfalfa hay was improved (P < 0.04) with reducing FG (1 vs. 2 mm). Moreover, EFE improved (P < 0.01) the DMD of DDGS without affecting that of barley straw or alfalfa hay. These results showed that the GPR, MD and FG were little interacted with EFE effect on in vitro GP and DMD of feeds, suggesting that the impact of these factors on in vitro EFE effect is minimal. Hence, enclosing feed substrate in filter bags can be recommended to screen EFE products for feed digestion because of practical convenience. Moreover, the impacts of GPR, MD and FG on in vitro GP and DMD of feeds suggested that these factors should be carefully considered when comparing the nutritive values of various feeds using in vitro techniques.