Effects of neutral detergent fiber content and its source on growth performance, rumen characteristics, digestibility, and methane concentrations in Hanwoo heifers

Objective: This study investigated the effects of neutral detergent fiber (NDF) content and NDF source (forage-or concentrate-derived) on growth performance, rumen characteristics, nutrient digestibility, and methane (CH4) concentrations in growing Hanwoo heifers.Methods: Thirty heifers (296 ± 25.7 kg body weight [BW]; 10 months old) were blocked by BW and assigned to three treatments: high forage-to-concentrate ratio (42.5:57.5)with highenergy concentrate (HFHC), low forage-to-concentrate ratio (30:70) with low-energy concentrate (LFLC), and low forage-to-concentrate ratio (30:70) with high-energy concentrate (LFHC).NDF-level effects were assessed by contrasting HFHC and LFLC with LFHC, whereas the NDF-source contrast compared HFHC with LFLC at similar total NDF levels.Dry matter intake (DMI) was recorded daily and BW every four weeks.Rumen fluid and fecal samples were collected, and CH4 concentrations measured, after 12 weeks.Results: Average daily gain (ADG) and feed conversion ratio were unaffected by NDF level or source (P > 0.05), whereas DMI tended to increase with lower NDF (P = 0.099).Lower NDF reduced NDF digestibility and increased total volatile fatty acid concentration (P < 0.05), decreased acetate proportion and acetate-to-propionate ratio, and increased propionate and butyrate proportions (P < 0.001).NDF source did not affect nutrient digestibility (P > 0.05).In the NDF-source contrast, LFLC had lower acetate and propionate and higher butyrate proportions than HFHC (P < 0.05).Lower NDF also decreased CH4 concentration per DMI A c c e p t e d A r t i c l eand ADG (P < 0.05).LFLC had lower CH4 concentration per ADG than HFHC, whereas CH4 concentration per DMI did not differ.Conclusion: Dietary NDF level was associated with broader changes in ruminal fermentation, NDF digestibility, and CH4 concentration per DMI and ADG, whereas NDF source had more limited effects, primarily on VFA proportions and CH4 concentration per ADG.Neither NDF level nor source significantly affected growth performance in growing Hanwoo heifers.