Boar sperm thawing practices: The number of straws does matter

The addition of reduced glutathione to cryopreservation media induces changes in the structure of motile subpopulations of frozen-thawed boar sperm

Adding cryopreservation media with reduced glutathione (GSH) has previously been shown to maintain the motility, membrane integrity and fertilizing ability of frozen-thawed boar sperm, although the effects of GSH on good (GFE) and poor freezability (PFE) ejaculates rely upon the intrinsic ejaculate freezability. The resilience to withstand freeze-thawing procedures has previously been related to the existence of a specific distribution of motile sperm subpopulations, which differs between GFE and PFE. Thus, the main aim of this study was to determine whether the addition of GSH to freezing media has any impact on the distribution of motile sperm subpopulations in GFE and PFE. With this purpose, 18 GFE and 13 PFE were cryopreserved with or without 2 mM GSH. Sperm quality and motile subpopulations were evaluated at 30 min and 4 h post-thawing. Three subpopulations were identified and the percentages of spermatozoa belonging to the fastest and most linear subpopulation, which was referred as 'SP1', decreased over post-thawing time. Good freezability ejaculates that were cryopreserved in the presence of 2 mM exhibited a significantly higher percentage of spermatozoa belonging to SP1 than the other combinations of treatment and freezability both at 30 min (mean ± SEM: GFE-C: 16.6 ± 0.4; GFE-GSH 27.7 ± 0.6) and 4 h post-thawing (GFE-C: 7.8 ± 0.2 vs.

GFE-GSH

16.7 ± 0.4). In conclusion, the positive effect of GSH on the motility of frozen-thawed sperm is related to a specific sperm subpopulation (SP1), which could coincide with the fertile sperm one.

Artificial insemination with frozen-thawed boar sperm

Artificial insemination with frozen-thawed semen in pigs is not a routine technique; its use is restricted to specific cases, such as preservation of valuable genetic material (germplasm banks), safety strategies in case of natural disasters, long-distance transport of sperm, and in combination with sex-sorting. Cryoinjuries resulting from freeze-thawing protocols are a major concern with regard to the fertilization capacity of the treated sperm, which is lower than that of liquid-stored semen. Here, we provide an overview of artificial insemination using cryopreserved sperm, and summarize the factors that influence cryopreservation success before, during, and after freeze-thaw (i.e., sperm selection before starting the cryopreservation process, holding time, use of cryoprotectants, and rates of freezing and thawing) and that are driving the identification of biomarkers to predict sensitivity to cryodamage. Three different artificial insemination techniques (conventional or intracervical; intrauterine; and deep intrauterine) are also discussed with regards to their relevance when using frozen-thawed semen. Finally, we review the use of additives to freezing and thawing media, given reports that they may maintain and improve the quality and fertilizing capacity of frozen-thawed sperm. In sum, artificial insemination with frozen-thawed boar sperm can provide reasonable fertility outcomes, if freezable ejaculates, specific additives, and appropriate insemination techniques are used.

Recent Advances in Boar Sperm Cryopreservation: State of the Art and Current Perspectives

While sperm cryopreservation is the best technology to store boar semen for long-term periods, only 1% of all artificial inseminations (AI) conducted worldwide are made using frozen-thawed boar sperm. With the emergence of long-term extenders for liquid storage, the use of cryopreserved sperm in routine AI is less required. However, banks of boar semen contain cryopreserved sperm and planning inseminations in AI centres may benefit from the use of frozen-thawed semen. Therefore, there is an interest in the use of this technology to preserve boar sperm. In this regard, although the first attempts to cryopreserve boar semen date back to the seventies and this technology is still considered as optimal, some relevant improvements have been made in the last decade. After giving a general picture about boar sperm cryodamage, the present review seeks to shed light on these recent cryopreservation advances. These contributions regard to protein markers for predicting ejaculate freezability, sperm selection prior to start cryopreservation procedures, additives to freezing and thawing extenders, relevance of the AI-technique and insemination-to-ovulation interval. In conclusion, most of these progresses have allowed counteracting better boar sperm cryodamage and are thus considered as forward steps for this storage method. It is also worth noting that, despite being lower than fresh/extended semen, reproductive performance outcomes following AI with frozen-thawed boar sperm are currently acceptable.

Acrosin activity is a good predictor of boar sperm freezability

The main aim of this study was to determine whether acrosin activity could predict boar sperm freezability. For this purpose, we characterized the changes in sperm quality and acrosin activity throughout the cryopreservation procedure of sperm samples from 30 Pietrain boars by analyzing four critical steps: step 1 (extended sperm at 15 °C), step 2 (cooled sperm at 5 °C), step 3 (30 minutes postthaw), and step 4 (240 minutes postthaw). Freezability ejaculate groups were set on the basis of sperm motility and membrane integrity after freeze-thawing. Results obtained highlighted the low predictive value in terms of freezability of sperm motility and kinematics and sperm membrane integrity, as no differences between good and poor freezability ejaculates were seen before cryopreservation. Significant differences (P < 0.05) between ejaculate groups were observed in the cooling step at 5 °C for sperm kinetic parameters, and after thawing for sperm motility and membrane integrity. In contrast, acrosin activity appeared as an indicator of boar sperm freezability because the differences (P < 0.05) between good and poor freezability ejaculates manifested yet in extended samples at 15 °C. On the other hand, we also found that variations in sperm kinematics, membrane lipid disorder, intracellular calcium content, acrosome integrity, and acrosin activity throughout the cryopreservation procedure were indicative of a significant damage in spermatozoa during the cooling step in both ejaculate groups. In conclusion, the main finding of our study is that acrosin activity can be used as a reliable predictor of boar sperm freezability because it differs significantly between good and poor freezability ejaculates yet before freeze-thawing procedures took place, i.e., in the refrigeration step at 15 °C.

Comparative analysis of boar seminal plasma proteome from different freezability ejaculates and identification of Fibronectin 1 as sperm freezability marker

Variation in boar sperm freezability (i.e. capacity to withstand cryopreservation) between ejaculates is a limitation largely reported in the literature. Prediction of sperm freezability and classification of boar ejaculates into good (GFEs) and poor freezability ejaculates (PFEs) before cryopreservation takes place may increase the use of frozen-thawed spermatozoa. While markers of boar sperm freezability have been found from sperm cell extracts, little attention has been paid to seminal plasma. On this basis, the present study compared the fresh seminal plasma proteome of 9 GFEs and 9 PFEs through two-dimensional difference gel electrophoresis (2D-DIGE) and liquid chromatography mass spectrometry (LC-MS/MS). The ejaculates were previously classified as GFE or PFE upon their sperm viability and progressive motility assessments at 30 and 240 min post thawing. From a total of 51 spots, four were found to significantly (p < 0.05) differ between GFEs and PFEs, and two were identified as fibronectin-1 (FN1) and glutathione peroxidase 5 (GPX5). These two potential markers were further studied by western blot and correlation analysis between protein relative abundances in fresh seminal plasma and regression factors from principal component analyses (PCA) run using post-thawing sperm quality parameters. Results confirmed that FN1 is a reliable marker of boar sperm freezability, because GFEs presented significantly (p < 0.05) higher FN1-amounts than PFEs and FN1 was found to be correlated with the first PCA component at 240 min post thawing. In contrast, GPX5 was not validated as a boar sperm freezability marker. We can thus conclude that levels of FN1 in fresh seminal plasma from boar semen may be used as a sperm freezability marker, thereby facilitating the use of frozen-thawed boar spermatozoa.

Relationship of sperm small heat-shock protein 10 and voltage-dependent anion channel 2 with semen freezability in boars

Freezability differences between boar ejaculates exist, but there is no useful method to predict the ejaculate freezability before sperm cryopreservation takes place. In this context, the present study sought to determine whether the amounts of small heat-shock protein 10 (also known as outer dense fiber protein 1) (ODF1/HSPB10) and voltage-dependent anion channel 2 (VDAC2) may be used as boar sperm freezability markers. With this aim, 26 boar ejaculates were split into two fractions: one for protein extraction and the other for cryopreservation purposes. Ejaculates were subsequently classified into two groups (good freezability ejaculates [GFE] and poor freezability ejaculates [PFE]) based on viability and sperm motility assessments after 30 and 240 minutes of after thawing. Although the VDAC2 amounts, analyzed through Western blot, were significantly higher (P < 0.01) in GFE (1.15 ± 0.18 density mm(2)) than in PFE (0.16 ± 0.03 density mm(2)), no significant differences were observed in ODF1/HSPB10 between both groups (i.e., 1.97 ± 0.38 density mm(2) in GFE vs. 1.87 ± 1.54 density mm(2) in PFE). In addition, principal component and multiple regression analyses indicated that the component explaining most of the variance (78.41%) in ejaculate freezability at 240 minutes after thawing resulted to be significantly (P < 0.05) correlated with VDAC2 content. This result revealed that the amounts of VDAC2 but not those of ODF1/HSPB10 may be used to predict the freezability of a given boar ejaculate before starting cryopreservation procedures.