Heterologous Seminal Plasma Reduces the Intracellular Calcium and Sperm Viability of Cryopreserved Stallion Spermatozoa.

Despite the vital role of seminal plasma (SP) in maintaining sperm function and aiding gamete interaction in many species, SP is usually removed before cryopreservation of stallion sperm to improve cryosurvival of sperm. The present study assessed if the vital sperm functional parameters of genetically superior stallions producing poor quality semen can be enhanced by the supplementation of heterologous SP from the stallion producing high quality semen. Spermatozoa from poor quality semen producing stallions were divided into three aliquots: two aliquots were supplemented with SP obtained from good quality semen producing stallions at the rate of 20% and 30%, respectively, whereas the third aliquot remained as control (0% SP) and incubated at 37°C for 30 minutes. Sperm membrane integrity, mitochondrial membrane potential (MMP), mitochondrial superoxide (mtROS) generation, and intracellular calcium status were assessed at different time intervals during incubation by flow cytometry. It was observed that the dead sperm population increased ( < 0.01) during incubation in both the 20% and 30% SP-supplemented groups. However, no significant changes were observed in MMP in both the control and treatment groups at different time intervals. Interestingly, it was found that sperm mtROS production increased ( < 0.01) during incubation in the SP-supplemented groups compared with the control group. The proportion of live spermatozoa with high intracellular calcium was reduced ( < 0.01) during incubation in the SP-incubated groups. Collectively, heterologous SP addition could not repair the damages caused by the cryopreservation and further resulted in deterioration of semen quality as observed in our study by reducing viability, increasing reactive oxygen species (ROS) production possibly due to high proportion of dead cells, or some factors (yet to be identified) that are inducive of oxidative stress in stallion spermatozoa.