Dynamics of Microorganisms and Metabolites in the Mixed Silage of Oats and Vetch in Alpine Pastures, and Their Regulatory Mechanisms Under Low Temperatures

Abstract

Silage is an effective method for alleviating winter feed shortages, but the mechanisms by which the silage microorganisms and metabolites respond to a mixture of oats and vetch at low temperatures remain unclear. In this study, the quality, microorganisms, and metabolites of oats mixed with vetch as a silage material, as well as after 90 days of silage, were analyzed. The traditional view holds that a decrease in microorganism diversity during silage indicates successful fermentation. However, in the present study, microorganism diversity was found to increase after silage under alpine and low-temperature conditions, with a significant rise in the abundance of microorganisms such as Levilactobacillus and Kazachstania. This phenomenon may be explained by the inhibition of rapid lactic acid bacteria proliferation by low temperatures, which allows for the survival of other cold-tolerant microorganisms and their involvement in metabolism. These microorganisms significantly increased the levels of metabolites such as l-methionine, l-glutamine, arachidonic acid, and linolenic acid in the mixed feeds, while simultaneously significantly decreasing the levels of metabolites such as l-leucine, l-arginine, l-asparagine, and glyceric acid. These metabolites possess antioxidant and anti-inflammatory properties that enhance the nutritional value of the feed and indirectly improve the immunity and performance of ruminants. This study comprehensively revealed the complex network of interactions between microorganisms and metabolites in the mixed forage of oats and vetch in alpine pastures and elucidated the regulatory mechanism of silage under low temperatures. The subsequent development of microorganism preparations for the targeted regulation of silage quality provides a theoretical foundation for producing high-quality silage in alpine pastures.

Keywords: metabolites; microorganisms; mixed silage; oats; vetch.

Figure 1

Diversity and variability of bacterial communities in a mixed oat and vetch. (A) Variation in alpha diversity of bacterial communities. (B,C) Differences in bacterial communities across treatments, calculated using unweighted UniFrac and weighted UniFrac distances, respectively, with coordinates calculated using principal coordinate analysis. (D,E) Relative abundance of bacterial phylum and genus.

Figure 2

Diversity and variability of fungal communities in a mixed oat and vetch. (A) Variation in alpha diversity of fungal communities. (B) Variability of fungal communities under different treatments. (C,D) Relative abundance of fungal phyla and genera.

Figure 3

Metabolite analyses of oats and vetch mixed diets. (A) Plot of OPLS-DA scores for metabolites. (B) OPLS-DA model replacement test plot. (C) Volcano plot showing up- and down-regulation of metabolites. (D,E) Summary of analyses of up- and down-regulated metabolites.

Figure 4

KEGG pathway enrichment analysis of different metabolites.

Figure 5

Correlation analysis between microorganisms and metabolites of mixed oat and vetch. (A) Heat map of bacterial–fungal networks; (B) Heat map of bacterial–metabolome correlations; (C) Heat map of fungal–metabolome correlations. *, **, and *** represent p < 0.05; p < 0.01; p < 0.001.