Microplastics are detected in bull and dog sperm and polystyrene microparticles impair sperm fertilization

The alarming increase in global infertility rates has coincided with the pervasive accumulation of microplastics (MPs) resulting from the poor management of plastic waste. This concerning trend is particularly troubling because only 10% of male infertility cases can be attributed to identifiable causes, leaving a significant knowledge gap in our understanding of their underlying factors. To bridge this critical gap, it is important to explore the connection between the accumulation of MPs and the observed decline in male fertility. Here, the presence of microplastics in reproductive fluids from bulls and dogs was assessed and used as baseline concentrations for bull sperm exposure. Bovine epididymal sperm (ES) presented a mean of 72.5 MP particles mL-1 (0.3691 ug mL-1) while canine seminal plasma had an average of 35.4 MP particles mL-1 (0.0066 ug mL-1). Bovine sperm was exposed to three different concentrations of a mixture of 1.1, 0.5, and 0.3 um polystyrene (PS) beads: (1) 0.7 ug mL-1, blood concentration of PS in cows (bPS); (2) 0.37 ug mL-1, concentration of total MPs in ES (esMP); and (3) 0.026 ug mL-1, concentration of PS in ES (esPS). All sperm samples incubated with PS exhibited reduced motility compared with the CT at 0.5 h. However, PS exposure did not affect acrosome or induced oxidative stress. When used for in vitro fertilization, the sperm exposed to PS had decreased blastocyst rates, in addition to inducing ROS formation and apoptosis on resulting embryos. By employing realistic exposure concentrations, this research sought to shed light on the comprehensive impact of MPs on bovine sperm and the quality of resulting embryos, providing the first evidence of MPs in bovine and dog sperm and demonstrating the detrimental effect of PS MPs on sperm motility and functionality. ### Competing Interest Statement The authors have declared no competing interest.