Methane mitigation, nutritional evaluation, and in vitro degradation kinetics of diets based on tropical grass...

The aim of this study was to evaluate the effect of xylanase addition (1.8 g/kg dry matter [DM]) to tropical grass haylage used in total mixed rations (TMR) on in vitro organic matter degradability, ruminal fermentation kinetics, and methane (CH4) emission. A completely randomized design was adopted in a 4 × 2 factorial arrangement, corresponding to four tropical grass cultivars (Andropogon, Mombaça, Massai, and Marandu) with or without xylanase addition and five replications per treatment (haylage bales), totaling 40 experimental bales. Ninety days after baling, the bales were opened and used to formulate total mixed rations, which were used as substrates for the in vitro incubations, according to the experimental treatments, totaling 40 TMR units (experimental diets). Chemical composition and ruminal fermentation parameters differed among grass cultivars. TMR based on Andropogon haylage showed greater crude protein concentration and higher acetate production (P < 0.0001), whereas Mombaça haylage promoted greater propionate production and a more favorable acetate: propionate ratio (P < 0.0003). The addition of xylanase did not alter organic matter degradability or total gas production (P > 0.05). However, xylanase tended to reduce CH4 emission (P = 0.0882) and improve CH4 efficiency (P = 0.0701), indicating a potential mitigation effect on enteric methane production. Diets based on Massai haylage without xylanase showed lower gas production and faster fractional fermentation rates. Overall, the results indicate that tropical grass haylage can be successfully used in TMR systems, and xylanase supplementation may contribute to improved ruminal fermentation efficiency and methane mitigation, although further studies evaluating different enzyme levels are still required.