Effects of fungal enzyme preparations on hydrolysis and subsequent degradation of alfalfa hay fiber by mixed rumen microorganisms in vitro

An in vitro study was conducted to investigate mechanisms by which fibrolytic enzymes improve fiber degradation in ruminants. Alfalfa hay was pre-treated with fibrolytic enzymes (Depol 40, Sumizyme X, Liquicell 2500, an experimental preparation and Multifect xylanase; DP, SX, LQ, PB and MX, respectively), diluted in buffer (pH 6.5), or with buffer alone (control) at 39°C, without (0 h pre-treatment) or with a 2 h incubation (2 h pre-treatment). The hay was then autoclaved to denature enzymic activities and washed extensively to remove hydrolysis products. The solid residue was dried and incubated with mixed rumen microorganisms for 12 and 48 h. The 0 h pre-treatment with MX, PB and SX increased NDF degradation at 48 h (P<0.05). Pre-treatment with MX, PB and SX for 2 h increased NDF degradation (P<0.05) at 12 h but, at 48 h, this effect was only evident for MX and PB (P<0.05). Compared to no incubation (0 h pre-treatment) incubation with DP, LQ, PB and MX increased NDF degradation at 12 h (P<0.05). However, at 48 h the benefit of incubation was only evident for MX (P<0.05). For the 0 h pre-treatment, degradation of the NDF at 12 h was positively correlated to acetyl xylan esterase activity (r2=0.84; P=0.08), and to endo-1,4-β-xylanase activity (r2=0.92; P<0.05). Furthermore, degradation of cellulose at 48 h was positively correlated to endo-1,4-β-xylanase activity (r2=0.88, P=0.06). In contrast, for 2 h pre-treated alfalfa, degradation of NDF was negatively correlated to several hydrolases of β-linked glucans (r2=0.86–0.95; P=0.05–0.07). Fibrolytic enzymes enhance fiber degradation by altering the structure of alfalfa hay. Xylanases and esterases are implicated as activities responsible for the initiation of this stimulatory effect.