Comparative Variation and Associations Among Seminal Microbiota, Oxidative Status, and Semen Quality in Different Rooster Types

This study examined the relationships among seminal bacterial composition, oxidative status, and semen quality in Thai native, crossbred, and commercial roosters. Fresh ejaculates (n = 10 per group) were evaluated for semen quality parameters—mass motility, total motility, progressive motility, sperm concentration, and viability and for malondialdehyde (MDA) levels, a marker of lipid peroxidation, as well as total bacterial load. Bacterial profiles were characterized using long-read 16S rRNA gene sequencing. Compared with commercial roosters, Thai native roosters exhibited significantly higher sperm motility and viability, along with markedly lower MDA concentrations (p < 0.05). Crossbred roosters showed intermediate values for most semen traits and oxidative indicators. Bacterial profiling revealed clear differences among rooster types in bacterial composition: commercial and crossbred roosters had higher bacterial richness and a greater prevalence of Gram-negative taxa, whereas Thai native roosters harbored lower bacterial diversity and load. Correlation analyses demonstrated that bacterial load was positively correlated with MDA concentration and negatively correlated with sperm motility and viability. These findings suggest that variation in seminal bacterial profiles, oxidative status, and semen quality is associated with differences among rooster types. The lower bacterial burden and lipid peroxidation observed in Thai native roosters may reflect greater reproductive resilience under tropical conditions, with potential implications for breeding and semen management strategies.