Effects of Grazing in a Low Deciduous Forest on Rumen Microbiota and Volatile Fatty Acid Production in Lambs

Abstract

The aim of the present study was to evaluate the effect of grazing the low deciduous forest (LDF) vegetation on the diversity of the rumen microbiome in growing lambs and its relationship with volatile fatty acid (VFA) profiles. After a 35-day indoor acclimatization (stabilization period), the lambs were assigned to two groups: housed (CG, n = 4) and grazing (EG, n = 4). The grazing lambs had a 14-day habituation period in the LDF (4 h/day) and a further 30 grazing days when fodder intake was observed. Ruminal samples were collected at the end of the stabilization, on day 14 post-stabilization (14DPS), and on day 44 post-stabilization (44DPS). The ruminal butyrate concentration showed a progressive decrease of approximately 23% over the time (p = 0.0130). The qualitative composition (p = 0.001) and relative proportions of bacteria (p = 0.004) in EG-44DPS exhibited a greater diversity, with 107 total genera and 19 unique, significant abundances in 13 genera with a higher presence of Bacteroidales_RF16_group, Lachnospiraceae_ND3007_group, and WCHB1-41. Moreover, significant functional profiles are associated with key metabolic pathways in bacteria and are interconnected by the need to generate energy and biosynthetic precursors and to manage available nitrogen and carbon. Finally, eight bacterial genera were identified as biomarkers correlated with the increase in VFA in EG-44DPS.

Keywords: 16S rRNA gene; bacterial; butyrate; fermentation; microbiome; rumen.

Figure 1

Venn diagram illustrating shared and unique genera among the experimental group in stabilization (EG-s), experimental group 44 days post-stabilization (EG-DPS44), control group in stabilization (CG-s), and control group 44 days post-stabilization (CG-DPS44).

Figure 2

Representative heatmap of the most abundant bacteria at the genus level in the EGs and EG-DPS44 groups. The dendrogram on the left shows the similarity in abundance between phyla, and the one at the top shows the similarity between the elements of each group.

Figure 3

Functional profile of the rumen microbiome data from the EG-s (blue) and EG-DPS44 (red) groups of lambs. The relative abundance of pathways in each group is shown on the horizontal axis. On the far right is the level of statistical significance (FDR) of each pathway. The dotted line indicates a reference point for the change in pathway expression (log2 fold change), with positive values indicating higher expression in EG-DPS44.

Figure 4

Correlation between bacterial markers at the genus level and %molar VFA, reference EG-s. Correlations with a threshold of statistical significance at p < 0.05 were visualized. The red color represents a positive correlation, and the blue color represents a negative correlation.