Application of Hops (Humulus lupulus L.) and β-Acid Extract to Improve Aerobic Stability and In Vitro Ruminal Fermentation of Maralfalfa Grass Silage

The potential of hops (Humulus lupulus L.) and β-acid extract were evaluated for improving the quality of maralfalfa grass (Cenchrus purpureus) silage (with added sorghum grain, sorghum straw, and urea) during aerobic exposure and their residual effects on in vitro ruminal fermentation characteristics. Silage samples and ground hops pellets (Galena and Chinook varieties) as well as β-acid mixtures were incubated at 37 °C for 24 h and then maintained under aerobic exposure for 12 h. The sample pH, counts of filamentous fungi, yeasts, and total coliforms, and volatile fatty acid (VFA) concentrations were determined. Subsequently, in vitro ruminal fermentation was conducted to determine total gas production and concentrations of hydrogen, methane, carbon dioxide, and VFAs. The β-acid treatment controlled yeast populations, but an increase (p < 0.05) in pH values was observed for the Galena and Chinook treatments compared to the Control. However, pH did not differ significantly (p > 0.05) between the Control and the β-acid treatment. Butyric acid concentrations in the silage were lower (p < 0.05) compared to the Control, except in the silage treatment with Galena. In the in vitro ruminal fermentation, the β-acid treatment showed higher butyric acid levels than the Chinook and Galena, but these differences were not significant (p > 0.05). There were no differences (p > 0.05) in methane between the treatments. An increase (p < 0.05) in propionic acid concentration was observed in the in vitro ruminal fermentation with β-acids. It was concluded that β-acids could help reduce silage deterioration during the aerobic phase, reducing the butyric acid and yeast populations, and their residual effect could improve ruminal fermentation, increasing propionate and acetate concentrations.