Equine semen quality following sperm exposure to seminal plasma stored under different conditions

Abstract

This study addressed equine sperm quality following exposure to seminal plasma stored under different conditions. Objectives were to compare fresh versus snap-frozen homologous seminal plasma; to compare homologous versus allologous frozen seminal plasma; and to determine the optimal processing/freezing method for long-term preservation of seminal plasma. For the latter objective, seminal plasma was subjected to the following storage conditions: immediate storage of seminal plasma at -20, -80, or -196oC (Groups 20, 80 and 196, respectively); storage of seminal plasma at 4oC for 24 h prior to freezing at -20, -80, or -196oC (Groups 4-20, 4-80, and 4-196, respectively); or storage of raw semen at 4oC for 24 h prior to isolating seminal plasma and freezing at -20, -80, or -196oC (Groups RW- 20, RW-80, and RW-196, respectively). Seven ejaculates were collected from each of three fertile stallions that served as sperm donors and seminal-plasma donors. Seminal plasma was also obtained from seven other stallions by centrifugation and filtration of raw semen. Following exposure of sperm to seminal plasma treatments and cooled storage of extended semen for 24 h, sperm motion characteristics (total motility [TMOT, %], progressive motility [PMOT, %], curvilinear velocity [VCL, μm/s]), plasma membrane intactness (PMI, %), acrosomal membrane intactness (AI, %), and sperm DNA quality (COMP, %) were evaluated. Comparison of fresh versus frozen homologous seminal plasma revealed no effect of treatment on any experimental endpoint (P > 0.05). Progressive motility was higher in semen exposed to frozen allologous seminal plasma, as compared to frozen homologous seminal plasma, for one of three stallions (P < 0.05). Storage method for seminal plasma did not impact PMI or COMP; however, Group RW-20 yielded lower TMOT than Group 4-80 (P < 0.05). Group RW-20 yielded lower VCL than all other treatments. Highest VCL was detected in Groups 80, 196, 4-80, and 4-196. A treatment x stallion interaction was detected for PMOT. No difference was observed for two stallions (P > 0.05); however, Group 20 yielded higher PMOT than Groups 80 or 196 for the remaining stallion (P < 0.05). Our findings suggest that: 1) seminal plasma can be frozen for later use, obviating the need to process fresh semen to supply seminal plasma, 2) allologous seminal plasma may be beneficial for selected stallions, and 3) semen should not be stored in the raw form for an extended period prior to processing seminal plasma for frozen storage.