# Fecal Microbial Community Characteristics of Oula and Hu Sheep and Their Correlation with Semen Quality

## TL;DR

This study compares gut microbes and semen quality in high-altitude Oula and low-altitude Hu sheep, finding that certain microbes linked to adaptation may affect reproductive traits.

## Contribution

The study reveals a link between high-altitude adaptation-related gut microbes and reduced sperm acrosome integrity in Oula sheep.

## Key findings

- Oula sheep have higher abundances of fiber-degrading microbes like Akkermansia and Treponema compared to Hu sheep.
- Sperm acrosome integrity was significantly higher in Hu sheep than in Oula sheep.
- Certain gut microbes in Oula sheep, such as Ruminococcus, are negatively correlated with sperm acrosome integrity.

## Abstract

Gut microbiota plays a crucial role in helping animals adapt to extreme environments, but it is unclear whether this adaptive advantage comes at the cost of reproductive performance. To investigate this issue, this study compared the fecal microbiota and semen quality of locally adapted high-altitude Euler sheep and introduced low-altitude lake sheep raised in the same environment on the Qinghai–Tibet Plateau. Sperm acrosome integrity and related parameters were assessed using the hypo-osmotic swelling test and Giemsa staining, and fecal microbial communities were systematically analyzed via 16S rRNA amplicon sequencing. Results showed that compared with Hu sheep, Oula sheep had significantly higher abundances of fecal microorganisms associated with enhanced fiber degradation, increased volatile fatty acid production, and reduced methane (CH4) generation, such as Akkermansia, Treponema, and Ruminococcus. The enrichment of these microbial groups was negatively correlated with sperm acrosome integrity, and this relationship may be associated with high-altitude adaptive regulatory mechanisms affecting reproductive capacity. This study provides theoretical support for the superior adaptability of Oula sheep in high-altitude pastoral environments.

Semen quality and fecal microbial composition were compared between native Oula rams reared on the Qinghai–Tibet Plateau and Hu sheep rams introduced from lowland regions. Semen quality was analyzed in eight adult Oula rams and eight Hu rams, and fecal microbial composition was assessed via 16S rRNA sequencing. Results indicated that sperm acrosome integrity was significantly higher in Hu sheep than in Oula sheep (p < 0.001); other semen parameters showed no significant differences. Significant differences were also observed in fecal microbial communities between the two breeds. Compared with Hu sheep, Oula sheep exhibited higher microbial abundance and diversity at the phylum level, particularly Campylobacterota, Euryarchaeota, Planctomycetota, Verrucomicrobiota, Myxococcota, and Deferibacterota (p < 0.05). At the genus level, Oula sheep had significantly higher abundances of Treponema, Campylobacter, Methanobrevibacter, UCG-009, Family_XIII_AD3011_group, [Eubacterium]nodatum group, Candidatus Soleaferrea, Akkermansia, and unidentified_Ruminococcaceae (p < 0.05). Correlation analysis indicated associations between sheep semen quality and the top 30 abundant fecal microbial genera. Six genera showed significant positive correlations with acrosome integrity rate, and eight genera exhibited significant negative correlations (p < 0.05). Two genera were correlated positively with plasma membrane integrity rate (p < 0.05). Prevotellaceae_UCG-004 was positively correlated with sperm motility and Progressive Motility spermatozoa proportion (p < 0.05); Ruminococcus showed a significant positive correlation with sperm linear motility and a significant negative correlation with acrosome integrity rate (p < 0.05). These findings indicate that the microbial groups enriched in Oula sheep fecal samples and exhibiting negative correlations with acrosome integrity—including Ruminococcus, Treponema, Akkermansia, and Euryarchaeota—are associated with sperm quality through physiological adaptation mechanisms specific to high-altitude environments.