In Vitro Assessment of Fecal Inocula From Horses Fed on High-Fiber Diets With Fibrolytic Enzymes Addition on Gas, Methane, and Carbon Dioxide Productions as Indicators of Hindgut Activity

• Fecal source × enzyme interaction occurred for gas and methane productions.
• Xylanase at 3-μL/g dry matter improved fecal fermentation.
• Fecal from horses fed cellulase + xylanase (1:1) had the highest methane production.

The aim of this study was to assess the effect of fecal inocula from horses fed on concentrate (restricted amount daily) and oat straw (ad libitum) supplemented with fibrolytic enzymes on in vitro hindgut activity. Cellulase (CE), xylanase (XY), and CE + XY (1:1 vol/vol; CX) were tested at three levels (μL/g dry matter [DM]): 0, 1, and 3, in addition to control without enzyme addition. Fecal inocula were collected from 16 Quarter Horse mares supplemented with enzyme at 0 (without enzyme), or fed 5-mL enzyme/mare/d of CE (FCE), XY (FXY), or CE + XY (1:1 vol/vol; FCX) for 15 days. The fecal content mixed with the culture media were used for incubation in bottles containing 1-g DM of substrate (a mixture of concentrate and oat straw [1:1 DM]). Gas (GP), methane (CH4), and carbon dioxide productions were measured at 2, 4, 6, 8, 10, 12, 24, and 48 hours after incubation. Interactions occurred (P < .05) between fecal source × enzyme product for the asymptotic GP, the rate of GP, CH4 production, and fermentation kinetic parameters. Moreover, interactions were observed (P < .05) between fecal source × enzyme product × enzyme dose for the rate of GP, CH4 production, and DM digestibility. Xylanase at 3-μL/g DM with FXY fecal increased (P < .05) the asymptotic GP, short-chain fatty acids, and microbial protein productions with lowering (P < .05) partitioning factor. At 24 and 48 hours and without enzyme, FCX and FXY, had the highest (P < .05) CH4 production. It can be concluded that XY enzyme at 3-μL/g DM was the most effective compared with other treatments.