Abstract
Total progressive motile sperm count (TPMSC) is a reliable index of fecundity evaluation of bull semen. It is an important determinant of frozen semen yield and conception rate of females artificially inseminated. Seminal plasma metabolites and sperm lipids are closely related to sperm survival and motility, but their relationship with TPMSC is not well known. In the present study, Simmental bulls with higher (H, n = 6) or lower (L, n = 6) TPMSC (P < 0.01) were selected from a cohort of 100 animals aged 2 to 5 yr based on semen quality. Analysis of semen quality and biochemical markers of seminal plasma revealed that H bulls had greater ejaculate volume (P < 0.05), sperm motility, plasma membrane integrity rate (P < 0.01), seminal plasma neutral α-glucosidase (P < 0.05), alkaline phosphatase, acid phosphatase, cortisol and phosphatidylcholine (P < 0.01), and lower sperm malformation rate (P < 0.05) and reactive oxygen species (P < 0.01). Semen metabolites and sperm liposome profiles of H and L groups were compared using LC-MS/MS analysis. A total of 120 differentially abundant metabolites (VIP > 1; P < 0.05) and 59 differentially abundant lipids (VIP > 1; P < 0.05) were identified between H and L groups. Oxidative stress, sperm motility, and sperm plasma membrane integrity were among the enriched biological pathways. Cyclic ADP-ribose (cADPR), up-regulated in H bulls, is associated with energy for sperm motility and maintenance of membrane stability. Thymidineglycol (Tg), levanbiose, thymidine (Thd), and CE (3M5) were down-regulated in H bulls and may have negatively affected sperm motility. Correlation analyses revealed that TPMSC and sperm motility were significantly positively correlated with cADPR, while Tg, Levanbiose, Thd, and CE (3M5) were significantly negatively correlated with TPMSC and sperm motility. Thus, we speculate that these molecules may be exploited as potential biomarkers for non-invasive evaluation of TPMSC in bull semen.