Effects of fibrolytic enzyme on ruminal fermentation characteristics of beef steers fed high and low quality growing diets

The effects of exogenous cellulases and xylanases (Trichoderma reesei) were evaluate in two studies: 1) in vitro true digestibility with several byproduct substrates; and 2) intake, digestibility, feeding behavior and ruminal fermentation characteristics of beef steers fed high and low quality growing diets. For the in vitro assessment, ruminal inoculum was collected from steers (n = 2; BW = 520 ± 30 kg) consuming low- and high-quality diets, mixed, incubated on DAISYII Incubator system. Within the lab, enzymes (0.75 µl/g of substrate DM) were included or not. Within in vitro batch (n = 5), substrates (n = 12) were incubated and in vitro true digestibility of DM, OM, NDF, ADF, and HEM was evaluated. For objective 2, ruminally cannulated crossbreed beef steers (n = 5, BW = 520 ± 30 kg) were used in a 5 x 4 unbalanced Latin square design, in which a 2 x 2 factorial arrangement of treatments was used: a) growing diet quality (high = HQ; and low = LQ); and b) enzyme inclusion (0 or 0.75 mL/kg of diet DM; ABVista, UK). Steers were fed ad-libitum during periods (n = 4; 14d for adaptation and 7d for collections) in which samples of diet, refusals, and feces (twice-day) were collected. Ruminal pH probes were used to continually assess ruminal pH. Ruminal fluid samples were collected at 2, 4, 8, 16 and 24h post-feeding for VFA and ammonia analyses. Subsamples of ruminal fluid (50 mL) were incubated (24h) for in vitro assessment of total gas and CH4 productions. A continuous observation (24h) was used for the feeding behavior analyses. Data were analyzed using the GLIMMIX procedures of SAS. Incubation batch and steer were considered the experimental unit for the in vitro and Latin-square assessment, respectively. Collection day was used as repeated measure for the in vivo assessment. An interaction (enzyme × substrate) was observed, in which intact sorghum grain in vitro disappearance of DM, OM, and NDF increased (P < 0.01) by at least 13.2% when enzymes were added, while corn-stalks tended (P = 0.10) for similar effect. Regardless of substrate type during incubations, the addition of fibrolytic enzymes increased (P < 0.01) disappearance of ADF by approximately 13.6%. When ruminally cannulated beef steers were fed, no major diet quality × enzyme interactions (P ≥ 0.18) were observed for intake variables. Enzyme-fed steers increased the intake of DM (P = 0.04), digestible DM (P = 0.05), and digestible NDF or ADF intakes (P ≤ 0.02) by approximately 6, 14, 21, and 24%, respectively, compared to steers not fed enzyme. Regardless of enzyme, steers fed HQ growing diets consumed more (P ≤ 0.04) DM, digestible DM, and OM, and less (P ≤ 0.03) total and digestible fiber variables than steers fed LQ growing diets. Ruminal pH average decreased (P = 0.01) when enzyme was fed and when growing diet was HQ. An interaction was observed for VFA, in which molar proportion of ruminal propionate increased (P = 0.01) by 4.3% for steers fed enzyme, and total VFA (mMol/L of ruminal fluid) tended (P = 0.06) to be 16% greater for enzyme-fed steers with HQ diet, but not in LQ growing diets. Steers fed HQ diets had greater (P < 0.01) valerate molar proportions, and lower (P < 0.01) acetate, and acetate:propionate ratio than steers fed LQ growing diets. Inclusion of enzyme did not affect (P ≥ 0.50) in vitro methane and total gas productions, although LQ diet-fed steers tended (P = 0.09) to increase in vitro methane production compared with steers fed HQ diets. Feeding behavior was not affected (P ≥ 0.50) by dietary enzyme treatment, except for a tendency (P = 0.09) to increase eating time when the enzyme was fed with LQ diets. Steers fed HQ diets showed less chewing activity variables (P ≤ 0.01) than those fed LQ. The use of fibrolytic enzyme (Trichoderma reesei extract) positively affected fiber digestion of commonly fed roughage sources in cattle diets, and might have additional benefit when used on sorghum grain-based diets. Fibrolytic enzymes in beef cattle growing diets stimulated intake and generated positive aspects of ruminal fermentation. Beef cattle high quality growing diet positively affected intake and ruminal fermentation characteristics, even when chewing activity was reduced.