412 Supplementation of high-grain diet with brewers’ spent grain protein hydrolysates reduced protein degradability and methane production in Rusitec

The objectives were to investigate the effect of supplementing brewers’ spent grain (BSG) protein hydrolysates on rumen fermentation, nutrient digestibility, gas production and microbial protein synthesis in Rusitec. The experiment was a completely randomized design with four treatments assigned to sixteen fermenters in two Rusitec apparatuses. Protein hydrolysates from BSG were prepared using two proteases (Alclase and Flavourzyme) at 1% protease of BSG protein under optimum pH and temperature conditions. The treatments were control diet consisting of 10% barley silage and 90% barley concentrate (DM basis), control diet supplemented with alcalase hydrolysates (AlcH) or flavourzyme hydrolysates (FlaH) at 10 g/kg of diet DM, or antibiotics (Ant; 33 mg monensin + 11 mg tylosin/kg diet DM). The study consisted of 8 d for adaptation and 7 d for sampling. It was highest (P < 0.01) with control and AlcH, intermediate with FlaH and lowest with Ant for digestibility of DM (76.5, 76.1, 75.3, 72.7%), CP (75.1, 75.4, 73.4, 69.7%) and starch (90.7, 90.8, 89.5, 87.8%). Digestibility of NDF did not differ among control, AlcH and FlaH (average 39.3%), but higher (P < 0.01) than Ant (31.8%). Production of NH3-N (mmol/d) was greater (P < 0.01) in the order of AlcH and FlaH (average 4.1) > control (3.7) > Ant (2.6). The VFA production (average 54.3 mmol/d) and acetate/propionate ratio (average 0.79) were not different among control, AlcH and FlaH, but greater (P < 0.01) than Ant (48.9 mmol/d, and 0.69). Total gas production were not affected by treatments, but CH4 production (mg/g digested DM) was lower (P < 0.01) for FlaH (3.5) and Ant (2.2) than control (3.8). Microbial protein production (mg/d) was lesser (P < 0.05) for FlaH (476) and Ant (459) than control (502). These results indicate that adding FlaH in high-grain diet effectively reduced rumen CH4 production and CP degradability without affecting fibre digestion.