Effect of mastication on degradation of orchardgrass hay stem by rumen microbes: fibrolytic enzyme activities and microbial attachment

Two in situ experiments were completed to study effects of mastication on particle-associated microbial mass and fibrolytic enzyme activity. In experiment 1, orchardgrass hay stems were cut into lengths of 10 cm (L, long), 2 cm (S, short) or ground to pass a 1 cm screen (G, ground), and offered to an esophageally fistulated steer in order to collect ingesta (LC, long and chewed; SC, short and chewed; GC, ground and chewed). These three forms of chewed ingesta and S (non-chewed short stem) were incubated for 2, 6, 14, 24, 48 or 96 h in the rumen of three wethers fitted with ruminal cannulae to which orchardgrass hay was fed. Chewed stem (LC, SC and GC) had higher fibrolytic enzyme activity from stem-associated microbes, higher rates and extents of neutral detergent fiber (NDF) disappearance, and shorter lag times than S (P<0.05). LC had a higher rate and extent of NDF disappearance than GC and SC (P<0.05). In experiment 2, tested materials were G (as in experiment 1), GC, reground GC (GCG, ground, chewed and reground; simulated rumination) and G treated with NaOH (G-NaOH). These materials were incubated in the rumen of three wethers for 2, 6 or 24 h. GC incubated in the rumen had higher concentrations of chitin (a fungal marker; P<0.05) and tended to have higher concentrations of diaminopimelic acid (DAPA, a bacterial marker; P=0.13), and higher colonization of Fibrobacter succinogenes (P<0.05) compared with G. GCG had a higher specific surface area, a higher number of F. succinogenes (P<0.05) and higher activities of fibrolytic enzymes (i.e. total and specific xylanase at 6 and 24 h, P<0.15), when compared to GC. G-NaOH had the highest NDF disappearance (41.7%, P<0.05) of the four stem types. Results show that chewing promotes fibrolytic microbial attachment, colonization and subsequent production of enzymes for ruminal fibrolysis by increasing physical damage, reducing particle size and increasing the surface area of the feed particles.