Phenological variation in native mixedgrass chemical composition, in vitro fermentation, and methane production

This study evaluated the impact of phenological development on chemical composition and in vitro ruminal fermentation of three cool-season ( Pascopyrum smithii (Rydb.) A. Love, Hesperostipa comata (Trin. & Rupr.) Backworth, and Koeleria macrantha (Ledeb.)), and three warm-season ( Bouteloua gracilis (Kunth) Lag. Ex Griffiths, Calamovilfa longifolia (Hook.) Scribn, and Distichlis stricta (L.) E. Greene) native grasses in the Mixedgrass Prairie of Western Canada. Grasses were harvested during June, July, and August of 2022 and 2023. Linear mixed models and simple regression models were used to analyze the data. Significant interactions between species and harvest month were observed for dry matter (DM), crude protein (CP), neutral detergent fiber, acid detergent fiber, and total digestible nutrients ( P < 0.05). CP decreased over time, except in B. gracilis, which peaked in July. Variation in fiber components and DM disappearance were species- and time-dependent. Koeleria macrantha yielded higher in vitro ruminal volatile fatty acid concentrations and acetate:propionate ratios than other species, while P. smithii exhibited the greatest DM disappearance. Methane production correlated positively with forage CP across all species. Results suggest that H. comata, D. stricta, C. longifolia, and P. smithii should be grazed early-season, and that reducing D. stricta may lower methane emissions.