Cellulase enhancing rumen microbiome of Tan sheep indicates plastic responses to seasonal variations of diet in the typical steppe

Abstract

Background: Climate and geographical changes significantly influence food availability and nutrient composition over time and space, Which in turn affects the selection of microbial communities essential for maintaining gastrointestinal homeostasis and facilitating dietary adaptation. Therefore, it is essential to understand the specific responses of the gut microbiota to dietary and seasonal variations in order to improve animal conservation strategies based on solid scientific knowledge.

Results: In summer, due to the higher nutritional quality of forage, Tan sheep exhibited enhanced forage degradation and fermentation. This was reflected by increased populations of key rumen bacteria, including Bacteroidetes, Prevotella_1, Prevotellaceae_UCG-003, Ruminococcus_1, Saccharofermentans, and Ruminococcaceae_UCG-014. Supplementation with cellulase further facilitated these processes, optimizing the utilization of available nutrients. In contrast, during winter, when the nutritional quality of forage decline, we observed lower indicators of forage degradation and fermentation in Tan sheep. Additionally, there was a significant increase in the Firmicutes/Bacteroidetes ratio, microbial diversity, microbial interactions, and metabolic activity.

Conclusions: The rumen microbiota adapts to enhance the breakdown of forage biomass and maintain energy balance during periods of inadequate nutritional value. Supplementing the diet with cellulase during these times can help mitigate the reduced digestibility associated with low-quality forage. This study highlights the dynamic adaptation of the rumen microbiota to seasonal variations in forage quality and emphasizes the potential benefits of cellulase supplementation in supporting rumen function and improving animal performance under varying environmental conditions.

Keywords: Cellulase; Microbiome; Ruminant; Season.

Fig. 1

Ruminal fermentation characteristics of Tan sheep fed cellulase in different seasons. ^{a, b, c} Boxes with different superscripts differ significantly (P < 0.05). Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter

Fig. 2

Bacterial and fungal diversity indices of the rumen microorganisms of sheep fed cellulase in different seasons. ^{a, b, c} Boxes with different superscripts differ significantly (P < 0.05). Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter

Fig. 3

Differences in community dissimilarities and operational taxonomic units. Venn diagram (A, B) indicates specific and shared OTUs in both cellulase and seasons. The weighted UniFrac distance (C, D) was used to calculate the differences in Tan sheep rumen microbiota in the different treatments, and principal co-ordinates analysis (PCoA) was used to calculate the coordinates. Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter

Fig. 4

The relative abundance of dominant bacterial (A, B) and fungal (C, D) communities at the phyla and genus level in the different seasons and treatments. Only taxa with an average relative abundance > 0.5% are displayed. Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter

Fig. 5

Relationship among NH₃-N, bacterial Communities, and volatile fatty acids (VFAs). ** and * indicate significance levels at 0.01 and 0.05, respectively

Fig. 6

Co-occurrence network of bacteria and fungi in the rumen microorganism in the different treatment and seasons. The number of nodes and edges and the degree of bacteria and fungi in the different treatment and seasons co-occurrence patterns. Neg/ pos, the ratio of negative correlation to positive correlation. Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter

Fig. 7

Interaction networks of the rumen microbiota. 16 S rRNA and ITS gene-based correlation network of the rumen microbiota, displaying statistically significant interactions with absolute value of correlation coefficients > 0.6. The node size was scaled based on the overall abundance of each taxa in the microbiota. A red edge indicates a positive correlation and blue edge indicates a negative correlation

Fig. 8

Relative abundance of predicted functions and significance of KOs (KEGG orthology groups) at KEGG (Kyoto Encyclopedia of Genes and Genomes) level 3 between the summer and winter. Student’s t-tests were used to compare the abundance changes two groups; only differences with a P < 0.05 are reported. Abbreviations: S_CK = control group in summer; S_CL = cellulase group in summer; W_CK = control group in winter and W_CL = cellulase group in winter