# Metabolomic Analysis of Cauda Epididymal Fluid in Yaks and Cattle

## TL;DR

This study compares the chemical makeup of sperm storage fluid in yaks and cattle, finding key differences that may explain lower yak sperm quality.

## Contribution

The study provides the first detailed metabolomic comparison of cauda epididymal fluid between yaks and cattle, linking specific metabolites to sperm function.

## Key findings

- Yak cauda epididymal fluid showed 79 upregulated and 212 downregulated metabolites compared to cattle in positive ion mode.
- 14 metabolites were found to promote sperm quality or function, while four were linked to impaired sperm function.
- The study identified distinct metabolic profiles in yak epididymal fluid that may affect sperm motility and maturation.

## Abstract

Yaks, native to high-altitude regions, hold significant economic and research value, yet exhibit lower reproductive capacity and reduced sperm motility compared to cattle. The epididymis, where sperm maturation occurs, features the cauda region as the primary storage site, with cauda epididymal fluid secreted by epithelial cells forming the microenvironment for sperm maturation. This study used liquid chromatography-mass spectrometry (LC-MS/MS)-based metabolomics to analyze and compare cauda epididymal fluid components between yaks and cattle. We found that under positive and negative ion detection modes, 1098 and 1297 metabolites were identified, respectively, with the most abundant categories being organic acids and derivatives, organoheterocyclic compounds, and lipids and lipid-like molecules. Compared with cattle, yak cauda epididymal fluid showed 79 significantly upregulated and 212 downregulated metabolites in the positive ion mode, and 110 upregulated and 230 downregulated metabolites in the negative ion mode. Among the differentially expressed metabolites across both species, a total of 14 metabolites positively correlated with sperm motility or functional maturation while four negatively associated with them. Our results establish a valuable metabolomic reference dataset for yak reproductive biology and provide new insights into the molecular regulation of sperm function.

The epididymis is crucial for sperm maturation, with its caudal region storing mature sperm. Yaks show poorer sperm motility and higher abnormality rates than cattle, but the metabolic mechanisms remain unknown. This study compared cauda epididymal fluid metabolites between six yaks and six cattle using untargeted metabolomics. A total of 1098 and 1297 metabolites types annotated by the Human Metabolome Database were identified in yak and cattle cauda epididymal fluid, respectively, using positive and negative ion modes. The Yak cauda epididymal fluid exhibited distinct metabolic profiles compared with cattle. A total of 79 metabolites were upregulated and 212 were downregulated in the positive ion mode, while 110 were upregulated and 230 were downregulated in the negative ion mode. Among these, 14 metabolites were reported to promote sperm quality, function or metabolism by reducing oxidative stress, blocking premature sperm capacitation and spontaneous acrosome reaction, enhancing mitochondrial energy metabolism or facilitating flagellar motility in cattle or other species. Four were reported to impair the quality or function of sperm via increasing the DNA methylation, inhibiting spermatozoa motility, upregulating the ROS levels and diminishing sperm motility. Taken together, this study established a valuable metabolomic reference dataset for yak reproductive biology and provided new insights into the molecular regulation of sperm function.