Effects of different water-soluble nitrogen in diets on <i>in vitro</i> digestibility and gas production

This study investigated the effects of replacing elephant grass (EG) with corn silage (CS) on in vitro rumen fermentation, digestibility, and greenhouse gas emissions. Five diets with 0–100% CS substitution (DM basis) provided water-soluble nitrogen (WSN) levels of 18.5–34.6% of total N. Substrates (200 mg DM) were incubated with goat rumen fluid for 72 h to measure gas, CH₄, CO₂, pH, NH₃-N, volatile fatty acids (VFAs), and digestibility (DMD/OMD). Data was analyzed using a quantitative gradient approach to evaluate fermentation responses across increasing CS substitution levels. CS diets showed distinct early gas dynamics (≤9 h), increased VFA concentrations, and reduced pH over time. Despite higher WSN, CH₄ production did not increase; instead, CH₄ per unit of digested substrate decreased with increasing CS inclusion, while DMD/OMD were highest in 100% CS after 48–72 h. NH₃-N increased with CS inclusion but declined at later incubation stages. These responses reflect integrated nutritional effects associated with concurrent changes in nitrogen solubility and carbohydrate composition. Overall, CS substitution improved in vitro fermentation performance, enhanced digestibility, and reduced CH₄ intensity, highlighting its potential as a practical feeding strategy in ruminant production systems where EG is commonly used.