Capacitation and Capacitation-like Sperm Surface Changes Induced by Handling Boar Semen

Protective Effects of Betaine on Boar Sperm Quality during Liquid Storage and Transport

Boar semen is commonly used in artificial insemination (AI) for pig breeding, but its quality can be negatively affected by liquid preservation and transportation, leading to reduced fertility rates. Vibration and temperature fluctuations are critical factors that significantly impact semen quality during storage and transportation, influencing the success rate of AI procedures. Betaine, a naturally occurring compound known for its role in maintaining male fertility, demonstrates potential for improving the preservation and transportation of liquid-preserved boar sperm. The present study demonstrated that betaine supplementation in the semen extenders at 0.5 mg/mL had a significant protective effect on boar sperm motility during storage at 17 °C for 3 to 5 days. During road transportation, 2.5 mg/mL betaine showed significant protective effects on boar sperm progressive motility, while 0.4 mg/mL betaine notably improved boar sperm mitochondrial activity and antioxidant capacity, and reduced lipid peroxidation damage. Simulation models also demonstrated that betaine supplementation increased the proportion of sperm displaying progressive motility and possessing intact acrosomes, regardless of the storage temperature (17 °C or 25 °C), and effectively mitigated the damage caused by vibration at a speed of 200 r/min. Overall, supplementing liquid-preserved boar semen extenders with betaine shows promise in mitigating damage to sperm quality during storage and transportation.

Vibration Emissions Reduce Boar Sperm Quality via Disrupting Its Metabolism

Artificial insemination (AI) with liquid-preserved semen has recently become common in pig breeding. The semen doses are produced in a centralized manner at the boar stud and then subsequently distributed and transported to sow farms. However, vibration emissions during transportation by logistic vehicles may adversely affect the quality of boar sperm. Therefore, this study aimed to explore the impact of vibration-induced emissions on sperm quality and function under simulated transportation conditions. Each time, ejaculates from all 15 boars were collected and then pooled together to minimize individual variations, and the sample was split using an extender for dilution. Different rotational speeds (0 rpm, 80 rpm, 140 rpm, 200 rpm) were utilized to simulate varying intensities of vibration exposure using an orbital shaker, considering different transportation times (0 h, 3 h, and 6 h). Subsequently, evaluations were conducted regarding sperm motility, plasma membrane integrity, acrosome integrity, mitochondrial function, adenosine triphosphate (ATP) levels, mitochondrial reactive oxygen species (ROS) levels, pH, glycolytic pathway enzyme activities, and capacitation following exposure to vibration emissions. Both vibration time and intensity impact sperm motility, plasma membrane integrity, and acrosomal integrity. Vibration exposure significantly reduced sperm ATP levels, mitochondrial membrane potential, and the levels of mitochondria-encoded proteins (MT-ND1, MT-ND6) (p < 0.05). After vibration emission treatment, the pH value and mitochondrial ROS levels significantly increased (p < 0.05). Inhibition of sperm glycolysis was observed, with reduced activities of hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH), along with decreased lactate levels (p < 0.05). Additionally, sperm tyrosine phosphorylation levels were significantly reduced by vibration emissions compared to the control group (p < 0.05). After the vibration emission treatment, the number of sperm bound to each square millimeter of oviduct explants decreased significantly compared to the control group (p < 0.05). Similarly, compared to the control group, using semen subjected to vibration stress for AI results in significantly reduced pregnancy rates, total born litter size, live-born litter size, and healthy born litter size (p < 0.05).

Kojic acid inhibits pig sperm apoptosis and improves capacitated sperm state during liquid preservation at 17°C

The parameters of sperm apoptosis and capacitation during liquid storage at 17°C can indicate the quality of pig sperm and the potential development of early embryos. However, the effect of kojic acid (KA) on semen preservation and its mechanism has not been fully understood. In this study, we discovered that adding KA to the diluent improved the antioxidant capacity of sperm mitochondria, maintained the normal structure of sperm mitochondria, and reduced sperm apoptosis. Western blot analysis revealed that KA prevented the release of Cytochrome c from mitochondria to the cytoplasm, reduced the expression of pro-apoptosis proteins cleaved Caspase-3 and cleaved Caspase-9, and increased the expression of the antiapoptosis protein Bcl-XL. Furthermore, KA also enhanced the motility parameters, oxidative phosphorylation level, adenosine triphosphate level, and protein tyrosine phosphorylation of capacitated sperm, while preserving the acrosome integrity and plasma membrane integrity of capacitated sperm. In conclusion, this study offers new insights into the molecular mechanism of how KA inhibits porcine sperm apoptosis and improves capacitated sperm parameters. Additionally, it suggests that KA can serve as an alternative to antibiotics.

Impact of inclusion of post-spermatic ejaculate fraction in boar seminal doses on sperm metabolism, quality, and interaction with uterine fluid

Boar ejaculate is composed of sperm cells and seminal plasma (SP) and is emitted in different fractions (pre-sperm fraction; spermatic-rich fraction; intermediate fraction; post-spermatic fraction), with different composition of SP and volume, which could influence the sperm quality during seminal doses preparation, conservation, and interaction with the female reproductive tract. In artificial insemination (AI) centers, seminal doses are usually prepared with the spermatic-rich and intermediate fractions, but the inclusion of other ejaculate fractions, although controversial, is beginning to be applied. The objective was to evaluate the synergic effect of accumulative ejaculated fractions on sperm functionality during seminal doses preparation, throughout storage and after incubation with uterine fluid (UF). For this purpose, a total of 57 ejaculates were collected, and the following experimental groups were prepared (n = 19 per group): (F1) spermatic-rich fraction; (F2) F1 plus intermediate fraction; (F3) F2 plus post-spermatic fraction. Each group was stored for 5 days at ∼16 °C, and the following parameters were evaluated: sperm metabolism of pure and diluted semen (day 1), sperm quality parameters (days 1, 3, 5), thermal-resistance test (TRT) and incubation with uterine fluid (UF) (day 5). Sperm metabolic rates between accumulative ejaculate fractions from pure and diluted semen did not show differences. Also, sperm quality parameters were not affected by the ejaculate fraction during storage. However, sperm subjected to TRT showed similar results except for progressive motility, which was better in F2 and F3 than F1. When sperm were incubated with UF, the quality decreased in each group, but sperm from F2 and F3 were less affected than those from F1. In conclusion, the post-spermatic fraction can be included in seminal doses for their use in AI-centers, with functionality of sperm of different SP origins not being impaired throughout the storage, and responding better to thermal and UF stress. However, further research in AI-centers is necessary to test the sperm behaviour under presented conditions.

In vitro aging of stallion spermatozoa during prolonged storage at 5°C

Artificial insemination with chilled stallion semen is hampered by a limited period of maximum fertility maintenance (24-48 h). This study used multiparametric flow cytometry to simultaneously measure reactive oxygen species (ROS) production, mitochondrial function or [Ca²⁺ ]_i and plasma membrane fluidity in viable, acrosome-intact spermatozoa, with the aim of providing insight into changes in sperm function during storage at 5°C. High proportions of viable and acrosome-intact spermatozoa (71 ± 8%) remained after 96 h of storage demonstrating that the basic integrity of the cells was well preserved (n = 17 stallions). In addition, more than 90% of viable, acrosome-intact spermatozoa had active mitochondria and low intra-cellular or mitochondrial ROS levels. By contrast, the percentage of viable, acrosome-intact sperm with low plasma membrane fluidity and low [Ca²⁺ ]_i decreased over time (1 h: 63 ± 16%, 96 h: 29 ± 18%; p < 0.05). The [Ca²⁺ ]_i in viable sperm rose 3.1-fold (p < 0.05) over the 4 days, and fewer spermatozoa responded to bicarbonate stimulation (1 h: 46 ± 17%, 96 h: 19 ± 12%) with an increase in plasma membrane fluidity following prolonged storage. Overall, prolonged storage of stallion semen at 5°C resulted in disturbed calcium homeostasis and increased plasma membrane fluidity. The decline in fertility of stallion semen during cooled-storage may therefore relate to aspects of in vitro aging (changes in plasma membrane fluidity and intracellular calcium) which impairs capacitation-associated cell functions.

"Fine feathers make fine birds" - The mammalian sperm plasma membrane lipid composition and effects on assisted reproduction

The sperm plasma membrane is important in modulating many sperm functions. The sperm membrane is composed of a complex mixture of lipids including phospholipids, glycolipids and sterols. There are differences of sperm membrane composition among mammalian species with two groups differing in the most abundant polyunsaturated fatty acid (PUFA), either docosahexaenoic (ω-3 PUFA) or docosapentaenoic acid (ω-6 PUFA). During testicular and epididymal maturation, composition of the sperm plasma membrane evolves with spermatozoa gaining the capacity for fertilization. The importance of fatty acid metabolism for complete spermatogenesis has been elucidated using gene knockout mice. During epididymal transit cholesterol content decreases and PUFA content increases, conferring more fluidity properties to the sperm membrane. The relatively lesser content of antioxidant enzymes and the relatively larger content of PUFA make the spermatozoa particularly susceptible to lipid peroxidation during sperm preservation. In numerous studies, there was adding of PUFA and antioxidants to the diet of animals or to semen extenders with the aim to improve sperm membrane integrity. This review highlights the current knowledge on the sperm membrane composition and effects on sperm function in mammalian domestic animals.

Predicting fertility from sperm motility landscapes

Understanding the organisational principles of sperm motility has both evolutionary and applied impact. The emergence of computer aided systems in this field came with the promise of automated quantification and classification, potentially improving our understanding of the determinants of reproductive success. Yet, nowadays the relationship between sperm variability and fertility remains unclear. Here, we characterize pig sperm motility using t-SNE, an embedding method adequate to study behavioural variability. T-SNE reveals a hierarchical organization of sperm motility across ejaculates and individuals, enabling accurate fertility predictions by means of Bayesian logistic regression. Our results show that sperm motility features, like high-speed and straight-lined motion, correlate positively with fertility and are more relevant than other sources of variability. We propose the combined use of embedding methods with Bayesian inference frameworks in order to achieve a better understanding of the relationship between fertility and sperm motility in animals, including humans.

Dimension reduction methods on porcine sperm motility landscapes reveal heterogeneity and hierarchy in sperm movement behavior and show high-speed and straight-lined motion as predictive features of fertility.

Factors influencing the response of spermatozoa to agitation stress: Implications for transport of extended boar semen

The shipping of liquid preserved semen is common practice in animal breeding and prior to cryopreservation for gene banking. Vibration emissions during transport may be harmful to spermatozoa. Therefore, strategies to minimize agitation-induced sperm injury are needed. The aim was to examine whether the type of semen extender, time after semen processing and the temperature in simulated transport conditions influence the response of boar spermatozoa to agitation stress. In Experiment 1, boar semen samples (n = 16) extended in Beltsville Thawing Solution (BTS) or Androstar Plus (APL) medium were filled in 90 mL tubes and shaken for 4 h at 200 rpm either at 22 °C or 17 °C. Samples were then stored at 17 °C for 144 h. In Experiment 2, semen samples (n = 11) extended in Androstar Premium were shaken either directly after filling at 22 °C or 20 h later after cooling to 5 °C. Samples were stored at 5 °C for 144 h. In Experiment 1, sperm motility and viability were lower (p < 0.05) in the shaken samples compared to the controls. The temperature, extender and the storage length had no effect on the agitation-induced loss of sperm quality. Sperm quality traits were higher in samples stored in APL compared to BTS. In Experiment 2, sperm motility at 24 h was reduced (p < 0.05) in those samples shaken at 22 °C but not at 5 °C. Sperm viability, membrane fluidity and mitochondrial membrane potential were not affected in either of the treatment groups. Extended boar semen designed for 17 °C storage and shipped on the day of collection is sensitive to agitation stress. In contrast, spermatozoa slowly cooled to 5 °C and shaken 20 h after processing are more resistant to agitation-induced shear forces and interfacial phenomena.

Cold-Shock Test Is a Practical Method for Selecting Boar Ejaculates Yielding Appropriate Seminal Plasma for Post-Thawing Supplementation

Simple Summary

The pig industry routinely uses artificial insemination with refrigerated semen. Cryopreserved semen has many advantages, but it is not widely used, partly because of unreliable results. The supplementation with seminal plasma (SP) could improve these results, but this fluid also presents variability. We evaluated if a simple cold-shock test (CST) could allow to easily identify the most suitable ejaculates for obtaining SP. Therefore, we tested 63 ejaculates, obtaining SP from the 4 showing higher quality (SPr, cold-shock-resistant) and lower quality (SPs, cold-shock-sensitive) after the CST. SPs and SPr pools supplemented thawed semen (20% SP) from six different boars, incubating at 37 °C and analyzing at times 0, 2, and 4 h. SPr was able to improve post-thawing sperm motility while maintaining viability. SPs had a similar but lower effect. SP in general seemed to stimulate sperm physiology, however decreasing membrane stability, acrosomal integrity, and disulfide bridges in the chromatin. This study supports the suitability of SP for improving thawed semen, with CST-selected ejaculates as preferable for this aim. Artificial insemination trials with thawed semen supplemented with SPr and SPs must validate the practical application of CST.

Abstract

Artificial insemination (AI) with cryopreserved semen is still unreliable for extensive pig industry application. Adding seminal plasma (SP) could improve post-thawing quality, but its suitability could vary. We applied a simple cold-shock test (CST, 5 min at 0 °C) on neat semen for classifying ejaculates (n = 63) as resistant or sensitive, obtaining two SP pools (CST-resistant: SPr, sensitive: SPs). Subsequently, frozen/thawed spermatozoa from six boars were incubated (37 °C) in MR-A® extender (control), 20% SPr, or 20% SPs, and analyzed at 0, 2, and 4 h. SP improved total and progressive motility, with a higher effect for SPr and STR (p < 0.05), decreasing kinematic parameters VCL and VAP, ALH, and BCF. Sperm viability was unaffected. SP increased apoptotic and membrane disorder ratios, and acrosomal damage, not affecting the chromatin structure (DNA fragmentation and immaturity by SCSA), protamination (CMA3), or disulfide levels (mBBr). However, the proportion of spermatozoa with elevated free thiols (disulfide bridges reduction) significantly increased. Results support a stimulatory role of SP on thawed semen, with additional benefits from SPr. The effect of SP and especially SPr after AI should be tested since CST could be a practical test for selecting suitable ejaculates in AI centers.

Sperm Proteome after Interaction with Reproductive Fluids in Porcine: From the Ejaculation to the Fertilization Site

Ejaculated sperm are exposed to different environments before encountering the oocyte. However, how the sperm proteome changes during this transit remains unsolved. This study aimed to identify proteomic changes in boar sperm after incubation with male (seminal plasma, SP) and/or female (uterine fluid, UF; and oviductal fluid, OF) reproductive fluids. The following experimental groups were analyzed: (1) SP: sperm + 20% SP; (2) UF: sperm + 20% UF; (3) OF: sperm + 20% OF; (4) SP + UF: sperm + 20% SP + 20% UF; and (5) SP+OF: sperm + 20% SP + 20% OF. The proteome analysis, performed by HPLC-MS/MS, allowed the identification of 265 proteins. A total of 69 proteins were detected in the UF, SP, and SP + UF groups, and 102 proteins in the OF, SP, and SP + OF groups. Our results showed a higher number of proteins when sperm were incubated with only one fluid than when they were co-incubated with two fluids. Additionally, the number of sperm-interacting proteins from the UF group was lower than the OF group. In conclusion, the interaction of sperm with reproductive fluids alters its proteome. The description of sperm-interacting proteins in porcine species after co-incubation with male and/or female reproductive fluids may be useful to understand sperm transport, selection, capacitation, or fertilization phenomena.

Different approaches for assessing sperm function

Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the "one shot" parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways.

Proteomic Analysis of Fresh and Liquid-Stored Boar Spermatozoa

In this study comparative proteomics was used to define changes in the expression of the spermatozoa proteins during liquid storage. Semen from eight boars was analyzed on the day of collection and after liquid preservation at 15-17 °C for three days. Sperm parameters (concentration, motility, morphology, vitality) and percentage of non-capacitated and acrosomal-reacted spermatozoa were determined. Sperm proteins were extracted and separated by two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and proteomic profiles were computationally compared to highlight differentially expressed protein spots that were, in turn, identified by mass spectrometry. The intensities of four spots were significantly different between fresh and liquid stored sperm. Namely: ATP citrate lyase, chaperonin containing T-complex polypeptide 1 (TCP1) subunit ε and probable phospholipid-transporting ATP-ase were over-expressed in liquid stored sperm, whereas cytosolic non-specific dipeptidase was over-expressed in fresh sperm. These differentially expressed proteins could be used as plausible biomarkers for the evaluation of boar semen quality and spermatozoa survival after liquid storage and could help to address problems associated with sperm preservation.

Boar semen improvement through sperm capacitation management, with emphasis on zinc ion homeostasis

Critical to fertilization success, sperm capacitation within the female oviductal sperm reservoir endows mammalian spermatozoa with hyperactivated motility and capacity to fertilize. An elaborate cascade of signaling events during capacitation guides the redistribution of sperm plasma membrane seminolipid and cholesterol, Ca-influx and increases tyrosine phosphorylation to promote hyperactivated motility. Such events result in the remodeling of the sperm acrosome, increased fluidity and fusability of the plasma membrane, shedding of surface-adsorbed seminal plasma proteins that glue sperm heads to the oviductal epithelium and ultimately the release of hyperactivated spermatozoa from the oviductal sperm reservoir. Discovered recently, the capacitation-induced sperm zinc ion efflux and resultant zinc signatures are reflective of sperm capacitation status and fertilizing ability, inspiring the retrospection of zinc ion functions in the physiology and fertility of boar sperm and that of other species. This review also highlights the merit of the domestic boar as a biomedical model for spermatology and fertilization research. Relevant to the quest for better fertility management in the livestock industries, the benefits of zinc ion supplementation through nutrition and direct addition to extended semen are discussed in the context of artificial insemination (AI). Ideas are shared on future technologies for zinc management in AI doses and research on the sperm zinc-interacting proteome.

Cryoprotective effect of low-density lipoproteins on post thaw semen quality in Hariana bull

The study aimed to evaluate the cryoprotective effect of low-density lipoprotein in Hariana bull semen. Four adult Hariana bull (3-4 years) after thorough andrological examination were selected for experiment. Semen was collected from each bull twice a week; total of 32 ejaculates (8 from each bull) were collected during the experiment. Collected sample from each bull was divided into 5 equal aliquots. Four aliquots were diluted separately with a Tris-based extender containing different concentration of low-density lipoproteins viz. 7% (T-1), 8% (T-2), 9% (T-3) and 10% (T- 4) as treatment while routinely used extender containing 20% hen egg yolk was used as control (C) to achieve final concentration of 125 million spermatozoa/ml. The diluted samples were cryopreserved and evaluated after 7 days. A significantly higher value of percent live sperms, sperm positive for hypo osmotic swelling test, sperms with intact acrosome and sperms exhibiting pattern F (uncapacitated sperm) were significantly higher in T-3 as compared to other treatment groups and control. The kinematic characters exhibited by sperm i.e forward progression %, VCL (μm/sec), VSL (μm/sec), VAP (μm/sec), Lin (%), Str (%), BCF (Hz) and ALH (μm) were significantly higher in T-3 as compared to other treatment group and control. In conclusion, extender containing 9% low density lipoproteins has better capacity to maintain the sperm character in post thaw Hariana bull semen and can be a preferred concentration to be utilized for cryopreservation with improved conception rate.

Reproductive tract modifications of the boar sperm surface

The sperm cell has a unique, polarized, and segregated surface that is modified extensively by the changing environments in both the male and the female reproductive tracts. The sperm cannot refresh its surface, as protein translation and membrane recycling by intracellular vesicular transport have ceased upon its maturation. So, how is the sperm surface modified in the reproductive tracts and how do these processes affect fertilization? This review traces these modifications as boar sperm travels from their liberation from the Sertoli cell into the lumen of seminiferous tubules of the testis to the site of fertilization in the ampulla of the oviduct in the sow, via an artificial insemination route. The effect of sperm dilution for artificial insemination, as well as more extensive sperm processing for in vitro fertilization, cryopreservation, or sex sorting, are also discussed with respect to how these procedures affect sperm surface organization and fertilization capacity.

Optimization of protocols for Iberian red deer (Cervus elaphus hispanicus) sperm handling before sex sorting by flow cytometry

Currently, sperm reproductive biotechnologies such as sex sorting and cryopreservation are undoubtedly valuable tools for improving the economic and biological efficiency of red deer production systems. In this context, and because of the particular characteristics of this species (extensive exploitation typically far from laboratory facilities), a key goal is to optimize the design of an adequate handling protocol of sperm samples before samples are subjected to sex sorting and cryopreservation procedures to obtain better outputs from the application of these technologies. The main aim of this paper was to design an adequate protocol for Iberian red deer sperm handling before sex sorting by flow cytometry to obtain optimal yields when sex sorting is used in this species. Semen samples from 11 adult males were obtained by electroejaculation during the breeding season. In this study, we tested different protocols for the handling of Iberian red deer spermatozoa before sorting by using different concentrations of sperm (400 or 800 × 10⁶) and adding or not Hoechst 33342 before the transport of samples to the sorting facilities. Based on the results, the most adequate method used to handle samples before sorting was transportation at a high sperm concentration (800 × 10⁶/mL) without Hoechst 33342. These transportation conditions in combination with Hoechst 33342 staining at 5.2 μL/mL once at the flow cytometry laboratory resulted in better (P < 0.05) sorting efficiency (99.9% of the samples showing split) than both, those samples transported at 400 × 10⁶sperm/mL (between 51.2 and 55.2% of the samples showing split) and those samples stained before transport at a sperm concentration of 400 × 10⁶sperm/mL (between 15.4 and 75.7% of the samples showing split). Sorting rates and sperm quality after sorting and cryopreservation was not affected (P > 0.05) by sperm handling before sorting. Moreover, the sorting yields were compatible with the practical application of these reproductive biotechnologies.

Relationship between HSP90a, NPC2 and L-PGDS proteins to boar semen freezability

BACKGROUND

The purpose of this study was to determine the association of three proteins involved in sperm function on the freezability of porcine semen: the heat shock protein 90 alpha (HSP90a), the Niemann-Pick disease type C2 protein (NPC2), and lipocalin-type prostaglandin D synthase (L-PGDS). Six adult boars (each boar was ejaculated three times, 18 in total) were classified by freezability based on the percentage of functionally competent sperm. The male semen with highest freezability (MHF) and the male semen with lowest freezability (MLF) were centrifuged immediately after collection to separate seminal plasma and spermatozoa to make four possible combinations of these two components and to incubate them for 3 h, adjusting the temperature to 17 °C, to freeze them afterwards. The quantification of proteins was performed in two stages: at zero and at 3 h after incubation of the four combinations.

RESULTS

The spermatozoa × incubation time (IT) interaction only had effect (P < 0.01) on HSP90a levels; this protein increased in seminal plasma, after 3 h of incubation, in larger quantity (P < 0.05) in combinations with MLF spermatozoa. In relation with the NPC2 protein, two isoforms of 16 and 19 kDa were identified. The 19 kDa isoform was affected (P < 0.01) only by the seminal plasma × IT interaction, with superior values (P < 0.01) both at zero and three hours of incubation, in the combinations with MHF seminal plasma; and 16 kDa isoform was affected (P < 0.01) only by the IT with reduction after 3 h of incubation. The levels of L-PGDS was affected (P < 0.01) only by the spermatozoa × IT interaction, which reduced (P < 0.01) in combinations with MLF spermatozoa after 3 h of incubation.

CONCLUSIONS

It is possible to consider that the three proteins evaluated were associated with freezability of boar semen due, especially, to the fact that mixtures with MLF spermatozoa showed greater increase levels of the HSP90a protein and reduction of L-PGDS in plasma. In addition, the seminal plasma of MHF had higher concentration of the NPC2 of 19 kDa protein, which was reduced by incubating with MHF spermatozoa.

The Fertility of Frozen Boar Sperm When used for Artificial Insemination

One of the limits to practical use of frozen boar sperm involves the lowered fertility when used for artificial insemination. Years of studies have shown that 5-6 billion sperm (approximately 3 billion viable) used in single or multiple inseminations results in pregnancy rates most often between 60 and 70% and with litter sizes between nine and 10 pigs. Yet today, it is not uncommon for studies to report pregnancy rates from 70 to 85% and litter sizes with 11-12 pigs. While global statements about the incidence and reasons for higher fertility are not conclusive, incremental fertility improvements appear independently associated with use of a minimum number of viable sperm (1-2 billion), insemination timing that increases the probability that sperm will be present close to ovulation for groups of females, selection for boar sperm survival following cryopreservation, and modification of the freeze and thaw conditions using additives to protect sperm from oxidative damage. Studies show that techniques such as intrauterine and deep uterine insemination can provide an opportunity to reduce sperm numbers and that control of time of ovulation in groups of females can reduce the need for multiple inseminations and improve the chance for AI close to ovulation. However, optimal and consistent fertility with cryopreserved boar sperm may require a multifaceted approach that includes boar selection and screening, strategic use of additives during the freezing and thawing process, post-thaw evaluation of sperm and adjustments in sperm numbers for AI, assessment of female fertility and ovulation induction for single insemination. These sequenced procedures should be developed and incorporated into a quality control system for improved fertility when using minimal numbers of cryopreserved boar sperm.

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.

Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs

Cryopreservation is the most efficient method for long-term preservation of mammalian sperm. However, freeze-thawing procedures may strongly impair the sperm function and survival and thus decrease the reproductive performance. In addition, the sperm resilience to withstand cryopreservation, also known as freezability, presents a high individual variability. The present work summarizes the principles of cryoinjury and the relevance of permeating and nonpermeating cryoprotective agents. Descriptions about sperm cryodamage are mainly focused on boar sperm, but reference to other mammalian species is also made when relevant. Main cryoinjuries not only regard to sperm motility and membrane integrity, but also to the degradation effect exerted by freeze-thawing on other important components for sperm fertilizing ability, such as mRNAs. After delving into the main differences between good and poor freezability boar ejaculates, those protein markers predicting the sperm ability to sustain cryopreservation are also mentioned. Moreover, factors that may influence sperm freezability, such as season, diet, breed, or ejaculate fractions are discussed, together with the effects of different additives, like seminal plasma and antioxidants. After briefly referring to the effects of long-term sperm preservation in frozen state and the reproductive performance of frozen-thawed boar sperm, this work speculates with new research horizons on the preservation of boar sperm, such as vitrification and freeze-drying.

Sperm quality and fertility of boar seminal doses after 2 days of storage: does the type of extender really matter?

The present approach was designed to evaluate the extender effects on sperm quality and fertility of short-term refrigerated seminal doses from Landrace boars lodged in husbandry-controlled conditions. For this purpose, we analyzed the sperm quality of seminal doses diluted in short-term (Beltsville Thawing Solution) and extra-long-term (Duragen) extenders from Days 0 to 2 of storage at 17 °C during an 8-month period. Pregnancy rates and litter size were evaluated from double inseminations within an interval of 12 hours (36 and 48 hours of refrigeration) of multiparous females using seminal doses diluted in each extender type. Sperm quality was assessed from the analyses of sperm motility and kinetics, sperm viability, expressed as plasma and acrosome membrane integrity, membrane lipid disorder, intracellular calcium levels, and acrosin activity. Results indicated significant differences between the extenders in the sperm quality of seminal doses. Therefore, the seminal doses diluted in Duragen had higher percentages of progressive motile spermatozoa and membrane-intact spermatozoa than those diluted in Beltsville Thawing Solution throughout all the experimental months. Nevertheless, despite these differences in preserving the sperm quality, pregnancy rates (>90%) and litter sizes (>10 piglets born per litter) were similar between the extenders. Our results had great relevance from a practical point of view because they reported lack of an extender effect on the reproductive performance of seminal doses during short-tem storage.

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.

Heparin binding analysis of boar sperm and its relation with farrowing capacity

New methods for the evaluation of semen quality according to in vivo reproductive data are useful tools for identifying boars of lower fertility among individuals with standard semen parameters. In this study, indirect fluorescence microscopy was used to evaluate the heparin binding site distribution upon capacitation of sperm from eight boars arbitrarily distributed into Groups I and II according to differential farrowing rates (Group I: ≥ 70%, Group II: < 70%). Additionally, the ability of sperm to bind to solubilised zona pellucida (ZP) was assayed in the presence or absence of heparin. Samples of two individuals of Group II showed lower percentage of B pattern in relation to other individuals (P < 0.001). The number of spermatozoa attached to ZP after 2 h of incubation in capacitating conditions with heparin was significantly lower than in its absence (P < 0.0001). These results suggest that heparin binding site distribution concerning capacitation may be indicative of the availability of proteins involved in the fertilisation process, specifically at the initial sperm-oocyte recognition. Differences in heparin binding site dynamics during capacitation may help identify a subpopulation of individuals with lower fertilising capacity and normal spermiogram, which is particularly useful at high-production establishments.