Effect of inclusion of oyster mushroom substrate on the in vitro fermentation kinetics of Brachiaria brizantha hay

<span>The objective of this study was to evaluate the effect of inclusion of exhausted substrate of Pleurotus ostreatus on the in vitro fermentation of Brachiaria brizantha hay-based diets. The experiment was conducted using the semi-automated gas production technique. The ruminal inoculum was collected from three fistulated cattle kept on Brachiaria brizantha pasture. Brachiaria brizantha hay and exhausted substrate of Pleurotus production were used for composition of the diets: ES (100% exhausted substrate), BH (100% Brachiaria brizantha hay), ES5 (5% ES + 95% BH), ES20 (20% ES + 80% BH), and ES30 (30% ES + 70% BH). The experimental design was a 5x3 factorial scheme consisting of five treatments and three ruminal inocula. The degradation kinetics of dry matter (DM) was determined after 96 hours of fermentation [D (96h)]. No significant differences in the cumulative volume of gas (A) were observed between BH (262.6 mL/g DM), ES5 (284.3 mL/g MS), ES20 (256.6 mL/g MS) and ES30 (261.7 mL/g MS), indicating that inclusion of the substrate did not affect hay fermentation. A lower gas volume (165.9 mL) and lower degradability (52%) were observed for the ES diet, showing a lower nutritional value of this substrate compared to Brachiaria brizantha hay, probably due to the action of enzymes that degrade structural carbohydrates found in the mycelia of Pleurotus. The ES diet exhibited a shorter colonization time (L=2.6 h; P&lt;0.05), a finding that may be attributed to the interaction between the mycelium and substrate, facilitating initial colonization. The inclusion of exhausted substrate did not increase microbial growth or degradation compared to the BH diet, but seems to have favored initial colonization of this substrate. The use of ES does not negatively affect colonization and may be used as an ingredient of ruminant diets.