Relationships between Biomarkers of Oxidative Stress in Seminal Plasma and Sperm Motility in Bulls before and after Cryopreservation

SIMPLE SUMMARY: The early detection of (in)fertility biomarkers is of great interest in the enhancement of artificial insemination programs, with the objective of providing equal access to food resources and potentially improving conservation strategies for endangered species. (In)Fertility is a complex trait governed by a multitude of physiological, molecular, and external factors, and it has low heritability. Accurately assessing fertility markers in vitro and predicting reproduction outcomes in vivo is thus a difficult task. The current study aimed at evaluating the relationship between sperm motility parameters and oxidative stress (OS) markers of seminal plasma (SP) in bulls before and after cryopreservation. In this study, advanced oxidative protein products (AOPP) and thiol concentrations were found to be positively related to the higher motility of fresh ejaculates; on the other hand, they did not affect the motility parameters of frozen–thawed semen. These observations give an alternative perspective on the relationship between sperm motility and SP composition, in which increased OS in SP does not necessarily negatively affect sperm motility. There are still gaps in the knowledge about the effect of cryopreservation on sperm quality and the role of SP in the process. Nevertheless, sperm motility and OS parameters (AOPP and thiols) could be considered as effective biomarkers of bull (in)fertility. ABSTRACT: This study aimed at evaluating the relationship between biomarkers of oxidative stress (OS) in seminal plasma and sperm motility in bulls before and after cryopreservation. Three ejaculates per bull were collected from 20 young bulls. Each ejaculate was analyzed for motility before and after cryopreservation (by CASA), and the SP concentration of Advanced Oxidation Protein Products (AOPP), thiols, and carbonyl groups (CT) were examined. Then, based on their motility, the ejaculates were grouped into: high motility fresh (HMF), low motility fresh (LMF), high motility thawed (HMT), and low motility thawed (LMT) groups. Higher AOPP and thiol concentrations on SP were related (p < 0.05) to the higher LIN and BCF and lower ALH of fresh semen. In addition, AOPP and thiols were significantly higher in HMF than LMF. As a confirmation of this, the Receiver Operating Characteristic (ROC) curve analysis showed that AOPP and thiol concentrations in SP were able to discriminate between HMF and LMF ejaculates (Area Under the Curve of 71.67% and 72.04%, respectively). These observations give an alternative perspective on the relationship between sperm motility and the OS parameters of SP, which need further investigations.