This study sought to investigate the impact of different levels of dietary maintenance energy metabolism on nutrient digestibility, rumen microbiota composition, and serum biochemical parameters in Lanzhou fat-tailed sheep rams. A total of twenty rams, each aged eight months and with an initial mean body weight of 27.81 ± 3.38 kg, were selected and randomly assigned to one of four experimental groups. These groups were administered with different levels of metabolizable energy (MEM): low energy (LE), intermediate energy (IE), high energy (HE), and extra high energy (EHE), corresponding to 6.77, 7.22, 7.72, and 8.20 MJ/d, respectively. The results showed a linear increase (p < 0.001) in average daily gain (ADG), dry matter (DM) intake, apparent DM digestibility, and crude protein (CP) digestibility. Conversely, the intake of nitrogen (NI), fecal nitrogen (FN), and manure nitrogen (MN) exhibited a significant linear decrease (p < 0.001). The N utilization efficiency rations of FN/NI and MN/NI linearly decreased (p < 0.001), while RN/NI linearly increased (p < 0.001). Additionally, the intake of gross energy (GE), methane energy (CH4-E), digestible energy (DE), and metabolizable energy (ME) exhibited a linear increase, whereas the ration of FE/GE intake linearly decreased (p < 0.001). The efficiency of energy utilization expressed as a proportion of GE intake (DE/GE intake, ME/GE intake, ME/DE intake, and CH4-E/GE intake) showed linear alterations (p < 0.05) with the increase in the dietary energy supplementation level. The dietary energy level did not exert a significant impact on serum biochemical indices (p > 0.05). At the phylum level, the average abundances of Verrucomicrobiota were significantly reduced in the EHE group compared to the IE group, while the average abundances of Desulfobacterota were significantly lower in the EHE group relative to the LE group. At the genus level, the average abundances of Succiniclasticum were significantly higher in the HE and EHE groups compared to the LE group. In conclusion, the energy level (8.20 MJ/d) significantly enhanced nutrient digestibility, energy, and nitrogen metabolism, and it significantly increased the relative abundances of Succiniclasticum.

This study aimed to investigate the effect of varying levels of dietary protein on digestion, metabolism, serum biochemical indexes, and rumen microflora in Lanzhou fat-tailed sheep. A total of twenty 8-month-old healthy rams with an initial average body weight (BW 25.16 ± 1.09 kg) were selected and randomly divided into four dietary treatments with different protein levels P: 9.47%, MP: 10.53%, HP: 11.56%, and EHP: 12.61%. The rams underwent a 23 day adaptation period, and the experiment was conducted for 7 d. The results showed that with increased dietary protein levels, the apparent digestibility of dry matter (DM), crude protein (CP), acid detergent fiber (ADF), and urine energy significantly increased (p < 0.05), increasing by 8.65%, 7.31%, 6.22%, and 0.1%, respectively. In contrast, the digestibility of neutral detergent fiber (NDF) first increased and then plateaued with the increase in protein levels, and the digestibility of NDF in the HP group was the highest (p < 0.05). The Shannon, Simpson, Chao1, and Ace indices of rumen microorganisms in the four groups did not change significantly (p > 0.05). Additionally, at the phylum level, the relative abundance of Bacteroidota, Firmicutes, and Verrucomicrobiota collectively accounted for over 91% of the total phylum composition. At the genus level, there was an increase in the relative abundance of uncultured_rumen_bacterium and Rikenellaceae_RC9_gut_group in the LP group, whereas the relative abundance of Prevotella decreased. In comparison to the other three groups, the HP group exhibited an increase in the relative abundance of Firmicutes. In summary, dietary protein level had no significant effects on the rumen microflora structure and blood biochemical indexes. However, diets with a high protein level can improve the apparent digestibility of nutrients and energy use efficiency of Lanzhou fat-tailed sheep.

Methane (CH₄), a significant greenhouse gas, ranks second only to carbon dioxide in its contribution to global warming. The application of Chinese herbs as a strategy to mitigate CH₄ emissions in ruminants has shown promise. However, there is limited information regarding the efficacy of Chinese herb straw in reducing CH₄ emissions in ruminants. This research aimed to investigate the beneficial effects of varying levels of Astragalus straw supplementation on methane emissions and to elucidate the underlying molecular mechanisms. The study examined the effects of different supplementation levels (0%, 5%, 10%, 15%, 20%) on in vitro rumen fermentation, CH₄ emissions, and ruminal microbial community in Lanzhou fat-tailed sheep using an in vitro fermentation method. The findings indicated that IVDMD, gas production, and CH₄ production significantly decreased with increasing levels of Astragalus straw supplementation (p < 0.05). Simultaneously, the lowest levels of AA, AA/PA, and NH₃-N, along with the highest concentrations of PA, BA, and MCP, were observed in the 20% supplementation group after 48 h of fermentation. In addition, supplementation with Astragalus straw resulted in an increased abundance of Bacteroidota, Spirochaetota, and Actinobacteriota, while decreasing the abundance of Firmicutes, Fibrobacterota, and Verrucomicrobiota. At the genus level, there was an observed increase in the abundance of Prevotella and Streptococcus, accompanied by a decrease in Rikenellaceae_RC9_gut_group. In conclusion, the supplementation of Astragalus straw has the potential to reduce CH₄ production by altering ruminal fermentation patterns, fermentation parameters, and microbial dynamics.