Post-thaw boar sperm motility is affected by prolonged storage of sperm in liquid nitrogen. A retrospective study

Abstract

Owing to the quick genetic turnover of the pig industry, most AI-boar sires live 2-3 yr, a period during which for 1-2 yr their semen is extended and used in liquid form for AI. Despite showing low cryosurvival, affecting fertility after AI, boar semen is frozen for easiness of transport overseas and reposition of valuable genetics. For the latter, semen is stored in liquid nitrogen (LN, cryostorage) for many years, a controversial practice. Here we studied how length of cryostorage could affect sperm quality. Straws (0.5 mL) frozen using the same cryopreservation protocol at one specific location from AI- sires of proven fertility were stored in LN for up to 8 yr. Post-thaw sperm quality was evaluated after 2, 4 or 8 yr of cryostorage, always compared to early thawing (15 d after freezing). Sperm motility and kinematics were evaluated post-thaw using CASA and sperm viability was cytometrically evaluated using specific fluorophores. Sperm viability was not affected by length of cryostorage, but total and progressive sperm motility were lower (p < 0.01) in sperm samples cryostored for 4 or 8 yr compared to those thawed 15 d after freezing. Cryostorage time affected sperm kinetics, but with greater intensity in the samples cryostored for 4 yr (p < 0.001) than in those for 2 yr (p < 0.01). The fact that the major phenotypic characteristic of boar spermatozoa, motility, is constrained by time of cryostorage should be considered when building cryobanks of pig semen. Attention should be placed on the finding that >2 yr of cryostorage time can be particularly detrimental for the post-thaw motility of some sires, which might require increasing sperm numbers for AI.

Long-term cryostorage of semen in a human sperm bank does not affect clinical outcomes

“…Another study (24) reported similar results, namely, that a cryopreservation period longer than 2 years negatively influenced the quality of frozen-thawed samples of boar sperm. Similarly, bull sperm samples cryopreserved for 6 years showed a greater loss of quality than those cryopreserved for 2 years (25).…”

Cryopreservation of boar semen

“…In their research Horvath et al (2018) found that it is possible to improve post-frozen-thawed semen quality by an appropriate application of hydrostatic pressure to boar semen during cryopreservation. Li et al (2018) concluded that the cryostorage time affected sperm kinetics while the sperm cryopreserved longer than 2 years can significantly decrease post-thaw motility.…”

Impact of Cryopreservation on Spermatozoa Freeze-Thawed Traits and Relevance OMICS to Assess Sperm Cryo-Tolerance in Farm Animals

“…On the contrary, dry ice cannot completely stop the metabolic activity of mammalian cells (12). However, it should be noted that some drawbacks still exist about the concept whether storage in liquid nitrogen is completely harmless to the viability of frozen sperm (13,14).…”