PS1-25. Impacts of Exogenous Enzymes on in Vitro Digestion of Cereal Grains.

Abstract Water conservation efforts in recent years have increased within the High Plains region of the US in response to declining Ogallala aquifer reserves caused by extensive use of surface irrigation. This has prompted renewed interest in grain sorghum, which is recognized for ability to survive in arid conditions. One limitation to grain sorghum (Sorghum bicolor (L.) Moench) utilization is its decreased digestibility compared to corn (Zea mays L.), which can be attributed to structure of the complex starch-protein matrix found within the grain endosperm. The objective of this experiment was to evaluate four protease enzymes supplemented at two inclusion levels as a means of disrupting the protein-starch matrix, potentially improve sorghum digestibility. Eleven treatments were utilized to evaluate in vitro dry matter disappearance (IVDMD), terminal culture pH, and volatile fatty acid (VFA) profiles. The experiment used a randomized complete block design with nine replicates across two experimental runs, incorporating substrate (sorghum or corn) inclusion levels (dry basis) of 0.3 mg in run 1 and 0.5 mg in run 2. Corn and sorghum samples were processed using a cyclone sample mill (Udy Corporation, Fort Collins, CO) equipped with a 1-mm screen. For in vitro cultures with sorghum, enzymes were added at 0, 3, or 30 mL per 50-mL centrifuge tube. Enzyme preparations included fungal neutral protease, fungal protease, fungal neutral protease, and Liquipanol. On the day of in vitro incubations, enzyme solutions were mixed in a 1:1 v/v ratio with deionized water and transferred by pipette into in vitro culture tubes. Ruminal fluid was collected from a fistulated steer and used as inoculant. In vitro cultures were terminated at 36 h in run 1 and 48 h in run 2. Terminal pH, IVDMD, and VFA profiles were analyzed as mixed models with treatment as fixed effect and run and block within run as random effects. Contrasts were performed to compare 1) average of sorghum treatments to control corn treatment; 2) effect of enzyme addition to sorghum; and 3) effect of enzyme concentration. The control corn treatment was superior to sorghum-based treatments, having greater IVDMD, lower terminal pH, and greater VFA concentrations (P < 0.01). Enzyme addition did not affect terminal pH, IVDMD, or VFA profiles (P > 0.10). No differences were observed between high and low inclusion rates for acetate or isobutyrate production (P > 0.10), but the high rate of enzyme addition depressed IVDMD and propionate production compared to the low enzyme inclusion rate (P < 0.01). Enzyme addition to sorghum failed to improve grain digestion, but future research may be warranted to expand on enzyme inclusion levels to determine if lower rates of addition may be more effective in improving sorghum digestibility.