Boar sperm cryosurvival is better after exposure to seminal plasma from selected fractions than to those from entire ejaculate

Abstract

Boar bulk ejaculates are now being collected instead of usual sperm-rich fractions (SRF) for artificial insemination purpose. The present study evaluated the influence of holding boar sperm samples before freezing surrounded in their own seminal plasma (SP), from either fractions/portions or the entire ejaculate, on post-thawing sperm quality and functionality. Ejaculates collected as bulk (BE) or as separate (first 10 mL of SRF [P1] and rest of SRF [P2]) from 10 boars were held 24h at 15-17°C and then frozen. Some bulk ejaculate samples were frozen immediately after collections as Control. In addition, epididymal sperm samples from the same 10 boars were collected post-mortem and extended in SP from P1 (EP1), P2 (EP2) and post SRF (EP3), and also held 24h before freezing for a better understanding of the influence of SP on boar sperm cryopreservation. The sperm quality (motility, evaluated by CASA, and viability, evaluated by flow cytometry) and functionality (flow cytometry assessment of plasma membrane fluidity, mitochondrial membrane potential and intracellular generation of reactive oxygen species [ROS] in viable sperm) were evaluated at 30, 150 and 300 min post-thaw. Post-thawing sperm quality and functionality of P1 and P2 were similar but higher (p < 0.01) than BE samples. Control samples showed higher (p < 0.01) post-thaw sperm quality and functionality than BE samples. Post-thawing sperm quality and functionality of EP1 and EP2 were similar but higher (p < 0.05) than EP3. These results showed that boar sperm from BE are more cryosensitive than those from the SRF, particularly when held 24h before freezing, which would be attributable to the cryonegative effects exerted by the SP from post SRF.

Characterization of the porcine seminal plasma proteome comparing ejaculate portions

“…This would indicate that sperm belonging to the ejaculate portion with more FN1 expression (more in P3 than P1+P2) should cryopreserve better. This does not seem be the case, as sperm from the entire ejaculate (P1+P2+P3) cryopreserve worse than those from SRF (P1+P2) [19]. This example could also be applied to other differentially expressed SP-proteins as AP, which has been related to sperm motility.…”

“…There are yet no studies evaluating how this procedural change can affect functional sperm performance. However, in this regard, it is well known that sperm from the SRF freezes better than those from the entire ejaculate, suggesting that the SP from the post-SRF, owing to its rich protein composition, impairs sperm freezability [19]. Furthermore, large proportions of SP in boar semen samples impair sperm sortability and sorting efficiency in ejaculates subjected to flow cytometry for sperm sex-sorting [20].…”

Membrane Stress During Thawing Elicits Redistribution of Aquaporin 7 But Not of Aquaporin 9 in Boar Spermatozoa

“…The electrolyte balance changes dramatically at ejaculation, where the exposure to seminal plasma changes the Na:Cl and Mg:K ratios as well the levels of bicarbonate, which was found to be 10-fold higher in seminal plasma than in the caudal fluid. It is well known that boar caudal spermatozoa survive freezing and thawing better than ejaculated spermatozoa do, with less damage to the plasma membrane 33 . Whether a higher amount of AQP-7 is related to this higher resilience to cryopreservation remains to be proven.…”

Roles of the reproductive tract in modifications of the sperm membrane surface

“…Several seminal plasma-specific proteins have been identified, and their importance in sperm physiology has also been addressed [26]. For example, seminal plasma protein profiles have been correlated with sperm and semen quality in adult boars [38], and post-thawing application or pre-freezing exposure of spermatozoa to the seminal plasma improves sperm quality, motility, and cryo-survival, eventually improving the fertilization ability of the sperm cells [39]. It is therefore clear at this point, that epididymal maturation is essential for successful fertilization, and that components from the male genital tract can serve as indicators for the evaluation of male fertility and can modify the protein profiles of the sperm membrane surface, which provides an alternative opportunity to regulate the function and fertilizing ability of the sperm.…”