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Simple Summary: Simple Summary: The rumen is the most important digestive organ of ruminants, and its rich microbial co−evolved with the host to play a crucial role in immunomodulation, defense, digestive metabolism, animal productivity, and meat quality control. It also forms a complex regulatory network with host genes and phenotypes that are involved in maintaining organismal homeostasis. In this study, we compared the differences in rumen microorganisms between crossbred progeny of sheep and Hu sheep, identified key biomarkers, and analyzed their relationship with rumen function. The results showed that microbial diversity was significantly higher in crossbred progeny, which was able to alter the microbial community structure to regulate rumen fermentation, promote carbon homeostasis, and enhance amino acid metabolism. In addition, there were significant correlations between biomarkers and key traits. Therefore, we suggest that there is a link between sheep rumen microbes and differential traits in crossbred progeny, which provides new insights for sheep trait improvement. This experiment was conducted to investigate the effect of three–way hybrid sheep and Hu sheep on serum indicators, rumen fermentation, rumen enzyme activity, and microorganisms in sheep. Healthy and similar birth weights from three groups (Hu, n = 11; Charolais × Australian White × Hu, CAH, n = 11; Charolais × Dorper × Hu, CDH, n = 11) were selected to be fed by the ewes until 45 days of age. Subsequently, they were weaned intensively and underwent short–term fattening for 3 months along with selected male lambs fed intensively. During this period, they were fed and watered ad libitum. Blood and rumen fluid were collected and analyzed for serum indicators and rumen fluid microorganisms, enzyme activity, and VFA, respectively, at the end of the fattening period. Compared with Hu lamb, the offspring of the three–way hybrid lamb showed significant improvements in body weight, serum lactate dehydrogenase, and creatinine content. However, there was no significant effect on serum immunity and antioxidant indices. In addition, the rumen fluid volatile fatty acid (VFA) molar concentration and microcrystalline cellulose and lipase content were significantly lower in the three–way hybrid lamb compared to Hu lamb, but β–glucosidase, amylase, pepsin, and VFA molar ratio were not significantly affected. Subsequently, 16S rRNA sequencing diversity analysis revealed that three–way hybrid lamb significantly increased rumen microbial ACE and Chao1 indices compared to Hu lamb. Meanwhile, the abundance of Verrucomicrobiota and Synergistota significantly increased at the phylum level. Correlation analysis showed that Prevotella had the highest proportion, while Rikenellaceae_RC9_gut_group correlated most closely with others genus. The microbial communities isovaleric acid molar concentration and proportion were strongly correlated. In addition, there were significant differences in correlations between microbial communities and isobutyric acid, butyric acid and valeric acid content, and their molar proportion, but they were not significantly correlated with digestive enzymes. From the functional enrichment analysis, it was found that hybrid progeny were mainly enriched in the pyruvate metabolism, microbial metabolism in diverse environments, carbon metabolism, and quorum sensing pathways. In contrast, the Hu sheep were primarily enriched in the cysteine and methionine, amino sugar and nucleotide sugar, and biosynthesis of secondary metabolite pathways. These results suggest that hybridization can play a role in regulating organismal metabolism and improve animal production performance by influencing the structure and characteristics of microbial communities. [ABSTRACT FROM AUTHOR]

Simple Summary: Rumen is the center of nutrient digestion, absorption and metabolism of ruminants. Ruminal microbes such as cellulolytic bacteria degrade the feed nutrients into smaller molecules, which are absorbed into the body mainly through rumen epithelium. Our study found that mulberry leaf powder supplementation improved the development of rumen epithelium, especially stratum basale, the most important layer of rumen epithelium for the energy metabolism. Our study suggests that supplementing ruminants with mulberry leaf powder may be one of the nutritional strategies that can improve the digestion and absorption performance of ruminants. Mulberry leaves have been used as a protein source in replacing concentrates of domestic animals, however, little is known about the relationship between supplementation level and the development of rumen epithelium. This experiment aimed to investigate the effects of different proportions of mulberry leaf powder (MLP) in dietary concentrate on rumen fermentation and rumen epithelium morphology in fattening Hu sheep. Forty three-month-old male Hu sheep with an initial body weight of 16.5 ± 0.6 kg (BW ± SD) were chosen and randomly divided into five treatments: 0% (control), 15% (T15), 30% (T30), 45% (T45) and 60% (T60) of MLP in concentrate, respectively. The results showed that the dry matter intake (DMI) and average daily gain (ADG) in treatments T15 and T30 have no significant difference with respect to the control treatment, but DMI and ADG in treatments T45 and T60 were lower than the control treatment (p < 0.05). The apparent digestibility of organic matter (OM) and neutral detergent fiber (NDF) increased linearly and quadraticly as MLP supplementation increased (p < 0.05). The concentration of ammonia (NH3-N) trended to decrease linearly with the increase of MLP supplementation (p < 0.1), whereas the microbial protein (MCP) concentration increased linearly as MLP supplementation increased (p < 0.05). In the results of rumen epithelium morphology, the width of stratum corneum was reduced, whereas the width of ruminal papillae increased (p < 0.05), and the width of stratum granulosum and stratum basale also increased as MLP increased. In summary, MLP supplementation could improve nutrient digestibility, the development of rumen papillae and stratum basale. However, high content MLP (45%–60%) supplementation decreased the growth and food intake performance of fattening Hu sheep. Therefore, 30% MLP is recommended to supplement in concentrate for fattening Hu sheep. [ABSTRACT FROM AUTHOR]