Objective To investigate the effects of substituting different proportions of licorice stems and leaves for the base diet's sainfoin hay on the gas production, kinetics, and fermentation parameters of in vitro ruminal fermentation in sheep.

Methods The experiment was designed with six groups, substituting licorice stems and leaves for 0% (control group), 5%, 10%, 15%, 20%, and 25% of the red clover hay (air-dried base), with three replicates per group. Ruminal fluid for the experiment was collected from three sheep fitted with permanent fistulas. After 48 h of fermentation, parameters such as pH, gas production, ammonia nitrogen (NH₃-N) concentration, volatile fatty acid (VFA) concentration, methane (CH₄), carbon dioxide (CO₂) production, and nutrient degradation rate were measured to study their impact on ruminal fermentation parameters.

Results As the proportion of licorice stems and leaves increased, the total gas production, gas production rate, and nutrient degradation rate showed an increasing trend over 48 hours, while the emissions of harmful gases such as methane (CH₄) and carbon dioxide (CO₂) were reduced. With an increase in the addition of licorice stems and leaves, the content of ammonia nitrogen (NH₃-N) decreased, and the concentration of microbial protein in the ruminal fluid (MPC) significantly increased. The addition of licorice stems and leaves promoted an increase in the concentrations of acetic acid, propionic acid, butyric acid, and isovaleric acid in the rumen, while reducing the content of butyric acid and the acetic acid to propionic acid ratio.

Conclusion licorice stems and leaves can effectively replace a portion of sainfoin hay in the diet of sheep, providing a theoretical basis for the scientific proportioning and application of licorice stems and leaves in the diet, which is of significant importance for optimizing the feeding management of ruminant animals.