Manipulating concentrate level in the diet of tropical cattle to improve fiber utilization and mitigate greenhouse gas emissions

This study evaluated the effects of concentrate level in diet, 10, 25, 40, and 60% forage dry matter (DM), on feed intake, nutrient utilization, weight gain (WG), and greenhouse gas (GHG) emissions in 12 male crossbred cattle (Red Sindhi × local, Bos indicus) 9-15 months of age in Southwestern Vi-etnam. The experiment was conducted for 6 months using a completely randomized block design. Ani-mals were individually housed and fed ad libitum with rice straw, with or without elephant grass, sup-plemented with commercial concentrate. Results showed that as the concentrate level increased, con-sumption of feeds, digestible nutrients and energy, WG, and GHG emissions rose linearly (P < 0.01), whereas neutral detergent fiber (NDFD) and acid detergent fiber digestibility declined (P < 0.05). The DM, organic matter, and crude protein digestibility were not significantly affected (P > 0.05). The in vitro NDFD assessments exhibited similar trends to the in vivo data (R² > 0.75). GHG emissions per unit of live weight were significantly reduced (P < 0.01) as concentrate levels increased up to 60%, alt-hough the difference between the 40% and 60% groups was not statistically significant (P > 0.05). These findings suggest that a concentrate level of 40% forage DM offers an optimal balance between fiber utilization and GHG emission intensity. The in vitro technique using rumen fluid from slaugh-tered cattle with unknown dietary history and minimized chemical reagents may serve as a practical and ethical tool for evaluating fiber utilization in cattle nutrition studies.