Conservation of fresh ram spermatozoa at 5°C in the presence of seminal plasma

Seminal plasma aids sperm transport and contains factors beneficial for sperm function. In artificial insemination, however, diluting the semen reduces the concentration of seminal plasma. To test the hypothesis that supplemental seminal plasma in extended ram semen improves conservation at 5°C, we added various concentrations of seminal plasma to semen during storage, and investigated subsequent sperm function in vitro. Semen was divided into three aliquots, extended in a commercial diluent (Triladyl) supplemented with 0, 10 or 25% (vol:vol) ovine seminal plasma and cooled to 5°C. After 8 and 24 h at 5°C, sperm were suspended in a modified synthetic oviduct fluid (SOF-m) at 39°C to mimic the female genital tract at insemination. Sperm aliquots were assessed for motility and chlortetracycline fluorescence after 0, 4 and 8 h in the SOFm. No significant differences were observed due to seminal plasma supplementation during conservation at 5°C or incubation in SOF-m at 39°C. However, decreased sperm motility and fewer non-capacitated sperm were observed concomitant with an augmentation of capacitated and acrosome-reacted cells during incubation in SOF-m. Therefore, the hypothesis that diluent supplementation with homologous seminal plasma improves ram sperm conservation or subsequent sperm function was not supported.