Methane production by in vitro ruminal fermentation of feed ingredients

Abstract

This study investigates the methane and carbon dioxide gas production, dry matter degradation, and final pH values obtained during the in vitro incubation of corn grain, soybean hulls, citrus pulp, corn silage, and crude glycerin. Experiments were performed using a randomized block design with four incubation periods. Each period featured four replicates per ingredient and four blanks, totaling 16 repetitions per ingredient. The lowest total amount of produced gas (37.96 mL gincubated DM-1) and the lowest final pH value (4.95) were obtained for crude glycerin (P < 0.05), which, however, exhibited the highest (P < 0.05) DM degradation. Citrus pulp produced the largest amount (P < 0.05) of CH4 per gram of incubated DM (13.56 mL g-1). However, when methane production was expressed per gram of degraded feed, the ingredients with lower degradation values, such as soybean hulls and corn silage, produced more CH4 per gram of degraded DM. Citrus pulp and corn grain produced more (P < 0.05) CO2 per gram of incubated DM. However, per gram of degraded food, citrus pulp produced the largest amount of CO2 (P < 0.05). Crude glycerin and corn grain produced less methane (per gram of degraded feed) than citrus pulp, soybean hulls, and corn silage. Differentiation of ingredients based on their methane production ability is important to express methane production per unit degraded food mass.