# Distinct Rumen Microbial Features and Host Metabolic Responses in Three Cervid Species

## TL;DR

This study compares gut microbes and metabolism in three deer species, revealing unique adaptations that could help improve their feeding and conservation.

## Contribution

The study identifies species-specific microbial and metabolic differences in Cervid ruminants under identical diets.

## Key findings

- Milu deer had higher blood lipid levels compared to other species.
- Reindeer showed elevated rumen volatile fatty acids and specific microbial pathways.
- Host genes linked to blood lipid traits were enriched in specific metabolic pathways.

## Abstract

The digestive system of ruminants contains billions of microorganisms that help them digest plants and obtain energy. Different Cervid species have evolved unique ways to adapt to their environments, but how their gut microbes and body metabolism differ remains unclear. In this study, we compared three deer species—Sika deer, Reindeer, and Milu deer—raised on the same diet. We analyzed the rumen microbiota, the fermentation products, and metabolites in serum. We found that although they were fed same diet, rumen microbiota and metabolic profiles were different among three ruminants. Milu deer had higher levels of blood fats, while Reindeer and Sika deer showed higher levels of blood proteins and specific liver enzymes. We also found that the blood genes regulate host metabolism. These findings reveal the specific metabolic adaptations of each species and provide insights for improving their feeding management and conservation strategies.

Rumen microbiota is pivotal for nutrient metabolism and physiological adaptation in ruminants. This study investigated the rumen microbial community, fermentation parameters, and serum biochemistry of three Cervid species—Sika deer (Cervus nippon), Reindeer (Rangifer tarandus), and Milu deer (Elaphurus davidianus) (n = 5/group)—fed an identical diet. Using 16S rRNA sequencing and biochemical analyses, we found that while Bacteroidota, Firmicutes, and Proteobacteria were dominant phyla across species. Sika deer and Milu deer exhibited significantly higher microbial diversity and abundance of carbohydrate-digesting genera (e.g., Butyrivibrio, Saccharofermentans), and pathways of carbohydrate digestion and absorption, starch and sucrose metabolism compared to Reindeer. Conversely, Reindeer showed increased abundances of Lachnospiraceae ND3007 and butyrate metabolism pathway, and significantly elevated rumen volatile fatty acid concentrations, particularly acetate and butyrate. Serum profiling revealed that Milu deer had significantly higher lipid levels (CHO, TG, LDL-C) but lower total protein and AST levels compared to other species. Notably, WGCNA linked these blood lipid traits to host genes enriched in PI3K-Akt, MAPK, and bile secretion pathways. These findings demonstrate distinct species-specific rumen fermentation patterns and host metabolic adaptations, suggesting a coordinated regulation between the rumen microbiome and host genetics in Cervid.