Microplastics in the seminal microenvironment of boar semen: associations with sperm motility and antimicrobial susceptibility.

Microplastics (MPs) are increasingly recognized as environmental contaminants capable of interacting with biological systems. However, their presence in livestock reproductive fluids remains relatively unexplored. In swine artificial insemination, boar semen quality is a key determinant of reproductive efficiency, and spermatozoa are highly susceptible to physicochemical stressors present in their surrounding microenvironment. Particulate contaminants such as MPs may therefore represent an overlooked factor relevant to semen quality. The present study investigated the occurrence, polymer composition, and size distribution of MPs in undiluted boar semen using μFTIR spectroscopy. In addition, exploratory analyses were conducted to evaluate potential associations between MPs and semen motility parameters assessed using computer-assisted sperm analysis (CASA) system, as well as bacterial load and antimicrobial susceptibility profiles of bacteria isolates. MPs were detected in all analyzed semen samples (n = 12), with concentration median (min-max) 9.58 (0.48-19.00) MPs/ml. Considerable variability was observed between individual boars and between the two participating breeding facilities. Polyethylene was the most frequently identified polymer. Exploratory analyses revealed that higher concentrations of specific polymers, particularly polyethylene and polyester, were associated with differences in sperm velocity distribution, characterized by a lower proportion of rapidly motile spermatozoa and a higher proportion of spermatozoa with slow velocity. Although there was no association between MPs levels and total bacterial counts, limited statistically significant associations were identified between the antimicrobial susceptibility profiles of the most frequently isolated bacterial species and specific MPs polymer types. These findings suggest that MPs may be related to sperm function and bacteria-antibiotic interactions within the seminal microenvironment. This study provides, to our knowledge, the first evidence of MPs in boar semen and identifies MPs as a potential environmental contamination factor relevant to semen quality.