Improving Ram Semen Low Cryotolerance by Replacing the Seminal Plasma With That of High-Cryotolerant Rams or Extender

Abstract

Ram semen cryotolerance problem continues despite intensive research. This study aimed to evaluate the effect of replacing total seminal plasma (SP) with that of high-cryotolerant rams or extender on semen quality parameters in low-cryotolerant rams. Rams previously determined as low (n = 6) and high-cryotolerant (n = 5) were used in the breeding season. High-cryotolerant rams were only included with their SP in the SP+ group. Each normospermic fresh ejaculate from low-cryotolerant rams was split into three aliquots to form the groups. The control aliquot was diluted using a two-step process. Centrifugation removed SP from the second aliquot (SP− group), and the sperm pellet was rediluted with a Tris-based extender using the same amount of SP removed. The third aliquot's SP was removed as in the SP− group, but the remaining sperm pellet was rediluted with fresh SP harvested from high-cryotolerant rams using the same amounts of removed SP in the SP+ group. Semen was rediluted with a Tris-based extender in the SP− and SP+ groups using a two-step process as in the control group. Sperm quality was similar between the groups after dilution and equilibration. However, the post-thaw semen quality was higher in the SP− (one parameter) and SP+ (four parameters) groups than in the control group (p < 0.05). Additionally, these parameters were similar in the SP− and SP+ groups. This study showed that, although an adequate extender had positive effects, replacing the whole SP with that of high-cryotolerant rams may better solve the low cryotolerance problem in ram semen.