New aspects of boar semen freezing strategies

The Effect of κ-Carrageenan on Porcine Sperm Cryo-Survival

κ-Carrageenan is a sulfated polysaccharide from red seaweed with substantial antioxidant activities. This study aimed to investigate the effect of κ-Carrageenan treatment on frozen-thawed (FT) porcine semen quality. Therefore, the spermatozoa were diluted and cryopreserved in a freezing extender supplemented with 0 (control), 0.2, 0.4, 0.6, and 0.8 mg/mL κ-Carrageenan. Sperm kinematics were assessed immediately after thawing (AT) and post-incubation for 120 min. The viability, acrosome integrity, lipid peroxidation, mitochondrial membrane potential (MMP), and intracellular caspase activity were measured AT. The results indicated that 0.2 mg/mL κ-Carrageenan increased total and progressive motility AT and post-incubation for 120 min (p < 0.05). Moreover, the viable sperm percentage and MMP after 0.2 mg/mL treatment were higher than those after control and other κ-Carrageenan concentration treatments. The proportion of acrosome-intact spermatozoa was significantly higher after 0.2 and 0.4 mg/mL κ-Carrageenan treatment than that after control and other κ-Carrageenan concentration treatments. The intracellular caspase activity was not significantly different among the experimental groups. However, the MDA concentration after 0.2 mg/mL κ-Carrageenan treatment was lower (p < 0.05) than that after the control treatment. Taken together, adding κ-Carrageenan to the porcine semen freezing extender improved the FT sperm quality mainly by influencing membrane stability and protecting against oxidative stress.

L-cysteine improves boar semen motility at 5 ºC but does not affect the oxidative status

Hypothermic storage has been proposed as a method to reduce bacterial loads and promoting prudent use of antibiotics. Reducing temperature, however, can lead to cold shock damage and oxidative stress in boar semen. This study verified the effect of L-cysteine on the quality of semen stored at 5 °C for 120 h. Twenty-one normospermic ejaculates were diluted in Beltsville Thawing Solution into five treatments: Positive control (Pos_Cont, storage at 17 °C without L-cysteine) and groups with 0, 0.5, 1, and 2 mmol/L of L-cysteine supplementation stored at 5 °C. Variables were analyzed as repeated measures, considering treatment, storage time, and interaction as main factors. The effects of different L-cysteine concentrations were also evaluated using polynomial orthogonal contrasts. Sperm motility and pH were higher in the Pos_Cont compared to the groups stored at 5 °C (P < 0.05). In polynomial orthogonal contrast models, total motility was affected by the interaction between L-cysteine and storage time (P = 0.04), with a linear increase in motility when increasing the amount of L-cysteine at 72 and 120 h. Progressive motility increased quadratically as the L-cysteine reached 1 mmol/L (P < 0.01). In the thermoresistance test at 120 h, sperm motility increased quadratically up to an L-cysteine dose of 1 mmol/L (P < 0.05). Sulfhydryl content linearly increased with L-cysteine supplementation (P = 0.01), with no effect on intracellular ROS and sperm lipid peroxidation (P ≥ 0.06) in 5ºC-stored doses. In conclusion, L-cysteine supplementation has a positive effect on sperm motility up to 120 h of storage at 5 °C.

Vaginal and vestibular electrical resistance as an alternative marker for optimum timing of artificial insemination with liquid-stored and frozen-thawed spermatozoa in sows

Development of a pen-side test to objectively determine the ideal time for artificial insemination (AI) in the sow would save producers time and money. Current processes rely on identification of oestrus via subjective behavioural and physiological markers that are indicative of high blood oestrogen concentrations. This study attempted to use measurements of electrical resistance (ER) in the cervical mucus to pinpoint timing of AI accurately enough to lead to equivalent pregnancy rates as a natural mating. Thirty-six sows were divided into 3 groups and observed for signs of oestrus. Seven sows did not show any oestrus behaviour and were excluded from the study. The remaining 29 sows were inseminated via natural mating and conventional oestrus detection (n = 14), or inseminated artificially with either liquid-stored semen (n = 8) or frozen-thawed semen (n = 7) according to timing indicated from electrical resistance measurements in the vagina and vestibule. Sows that were artificially inseminated on the basis of the electrical resistance readings had a lower pregnancy rate (P = 0.034) and less piglets born alive per litter (P < 0.05) than those that were naturally mated according to a conventional oestrus detection regime. However, the pregnancy rate and total piglets born alive did not differ between the two groups that underwent artificial insemination. Change in electrical resistance in the vagina has the potential to accurately predict ovulation timing, but more work is required to refine the timing of AI in relation to the readings before the technique can be adopted by industry.

In vitro effects of two different commercial freezing and thawing extenders on boar sperm quality

This study was conducted to evaluate whether there were differences in viability of cryopreserved semen when using two different freezing (Minitube Cryoguard - F1 or Androstar® CryoPlus - F2) and thawing (Minitube Cryoguard Thawing solution - T1 or Androstar® Plus - T2) extenders. Ejaculates were collected, diluted (1:1), and cooled before shipping at 17 °C overnight. Samples were aliquoted in cryopreservation extender F1 or F2. Four straws from each treatment sample were thawed and diluted in T1 or T2, resulting in four treatments (F1-T1, F1-T2, F2-T1, and F2-T2). The sperm in diluted semen were evaluated for motility kinetics at 30, 180, and 360 min after thawing. The integrity assessments of the plasma and acrosomal membranes were performed at 30 and 360 min after thawing. There was no interaction between F × T × Time (P > 0.05), and no interaction between F × T (P > 0.05). The sperm progressive motility (PMOT) as time post-thawing increased was greater (P = 0.015) when dilutions occurred using F1 compared with F2 extender. Sperm thawed in T1 had a greater TMOT (P = 0.008) and PMOT (P = 0.033) at all times evaluated. The sperm plasma and acrosomal membrane integrity (AIMI) were greater (P = 0.009) when samples were preserved in F1 compared to F2 extender. The use of T2, as compared with T1 thawing extender, resulted in an enhanced integrity of the plasma and acrosomal membranes (P = 0.008). It is concluded different combinations of commercial freezing extenders and thawing solutions have effects on the quality of cryopreserved boar semen in vitro.

Role of exogenous antioxidants on the performance and function of pig sperm after preservation in liquid and frozen states: A systematic review

In situations where an excessive generation of reactive oxygen species overwhelms antioxidant capacity, a harmful effect on sperm function is exerted. Antioxidants are molecules capable of minimizing this detrimental effect, which is important in pig sperm due to the high content of polyunsaturated fatty acids in their plasma membrane. The present systematic review aims at evaluating whether supplementing semen extenders (for liquid storage at 17 °C) or freezing and/or thawing media (for cryopreservation) with antioxidants influences sperm quality and functionality parameters, and in vitro/in vivo fertility outcomes. We defined inclusion and exclusion criteria in a PICOS table according to PRISMA guidelines, and conducted a literature search through MEDLINE-PubMed in November 2020. After systematic selection, 75 studies were included: 47 focused on cryopreservation and 28 on liquid storage at 17 °C. More than 70% of the studies included in this review showed that adding semen extenders for liquid storage and/or freezing/thawing media for cryopreservation with antioxidants enhances sperm quality and functionality parameters. In addition, this supplementation improves in vivo/in vitro fertility outcomes, supporting the hypothesis that the beneficial effect observed upon sperm quality has a positive impact on reproduction outcomes.

Improvement of the motility of boar sperm after cryopreservation

After the sperm cryopreservation process, there frequently is a marked decrease in sperm motility, however, this loss of motility could be avoided or reduced by modifying the thawing extender. The aim of conducting this study was to evaluate treatments resulting in differences in pH of the thawing extender on post-thawing sperm quality, especially motility. The associated effects were evaluated of the thawing extender pH when there were pH values of 7, 8 and 9 on values for sperm viability, acrosome integrity, motility and kinematic variables. To evaluate pH effects of the thawing extender on sperm motility, the procedures for evaluating the sperm variables were conducted with or without inclusion of caffeine in the extender. In addition, effects of thawing extender pH on the sperm subpopulations were analyzed. The results indicated that by increasing the pH of thawing extender to 9, sperm viability and acrosome status were not affected, and motility was markedly greater with there being similar values when there was a pH of greater alkalinity and pH 7 when caffeine was included for conducting the evaluations. Furthermore, for values of kinematic variables and sperm subpopulations, when there was a pH of 8 of thawing extender, sperm motility was maintained to a greater extent as storage duration advanced and the proportions of different sperm populations were also maintained during storage. In conclusion, when there was use of the thawing extender at pH 8, there was enhanced post-thawing sperm motility and preservation of motility as storage time advanced.

Alpha-tocopherol improves sperm quality by regulate intracellular Ca2+ intensity (influx/efflux) of Simmental bull cattle sperm

Background

The effects of α-tocopherol on intracellular Ca²⁺ intensity in semen cryopreservation by regulate intracellular Ca²⁺ intensity have not been reported yet.

Objective

The research was conducted to evaluate the effect of supplementation α- tocopherol into egg yolk skim milk extender on sperm quality and intracellular Ca²⁺ intensity.

Methods

Semen samples were collected and supplemented with respectively 0mM (P0); 0.5mM (P1); 1mM (P2); 1.5mM (P3) and 2mM (P4) α-tocopherol in extender before cryopreservation processes. Post-thawing sperm was evaluated for motility, viability, and abnormality using Phase Contrast Microscope (200x) with eosin-nigrosine staining, and intracellular Ca²⁺ intensity of the best result dose was evaluated using Confocal Laser Scan Microscope (400x) with Fluo-3 Staining.

Results

The results showed there was a significant difference (P≤0.05) in sperm motility and viability between P0; P1 with P2; P3; P4. The Motility and viability between groups P0; P1 and P3; P4 showed no significant difference (P≥0.05), while P2 with P3; P4 showed significant difference (P≤0.05). There was a significant difference (P≤0.05) in sperm abnormality of P0; P1 with P2; P3; P4. The abnormality between P0; P1 and P2; P3 showed no significant difference (P≥0.05), while P2; P3 showed a significant difference with P4 (P≤0.05). The best result in sperm quality was supplementation with 1.5mM α-tocopherol. Ca²⁺ intracellular intensity: 142.76± 21.8 au (P0) and 176.06±61.43 au (P3).

Conclusions

It was concluded that 1.5mM α-tocopherol is the best dose to improve sperm quality by regulating intracellular Ca²⁺ intensity on Simmental bull cattle.

Effects of CoQ10 on the quality of ram sperm during cryopreservation in plant and animal based extenders

The purpose of this study was to evaluate the effect of different concentrations of CoQ10 in soybean lecithin (SL) or egg yolk (EY) extenders on ram semen cryopreservation. Semen samples were collected from five rams, twice a week, then diluted in the extenders (SL and EY) containing different concentrations of CoQ10 as follows: extender containing SL: 0 μM (control, SL/Q0), 1 μM (SL/Q1), 2 μM (SL/Q2), 5 μM (SL/Q5) and 10 μM (SL/Q10) CoQ10; extender containing EY: 0 μM (control, EY/Q0), 1 μM (EY/Q1), 2 μM (EY/Q2), 5 μM (EY/Q5) and 10 μM (EY/Q10) CoQ10. Sperm motion characteristics, membrane integrity, abnormal morphology, viability, apoptotic-like changes, mitochondria active potential, acrosome integrity and lipid peroxidation were evaluated after freeze-thaw process. The SL/Q1, SL/Q2, EY/Q1 and EY/Q2 resulted in greater (P ≤ 0.05) sperm total motility, progressive motility, membrane integrity and mitochondria active potential compared to the other groups. Acrosome integrity in the SL/Q0, SL/Q1, SL/Q2, EY/Q0, EY/Q1 and EY/Q2 groups was greater (P ≤ 0.05) than in the SL/Q5, SL/Q10, EY/Q5 and EY/Q10 groups. The SL/Q2 and EY/Q2 treatment groups had greater (P ≤ 0.05) sperm viability rates and less apoptotic-like changes and lipid peroxidation. The CoQ10 compound could be explored as a novel potential antioxidant for cryopreservation of ram semen because with used of this compound in the present study there was an improved post-thawed sperm quality.

Post-cervical artificial insemination in porcine: The technique that came to stay

The porcine industry is of great importance worldwide, and so any technological innovation in one or more of the associated production areas is of interest for meat production. Among such innovations in the reproduction area, post-cervical or intrauterine artificial insemination (PCAI) has emerged as a new approach in artificial insemination (AI). PCAI is gradually replacing traditional cervical insemination (CAI), particularly in countries with intensive pig production industries. This type of insemination, which deposits the semen in the body of the uterus (as opposed to traditional cervical deposition), is increasingly used in the field due to its simplicity and the numerous advantages that it provides at production level (e.g. reduced number of sperm, less time required to perform insemination and faster genetic improvement) and, consequently, from an economic point of view. In addition, since its inception, PCAI has been combined with other reproductive biotechnologies, such as the use of frozen-thawed sperm, fixed-time AI or sperm-mediated gene transfer. However, despite its wide acceptance and application, new approaches for increasing the efficiency of PCAI are constantly being sought, such as the adjustment and standardization in sperm numbers, the conservation of the PCAI semen dose, its association with other biotechnologies (sex-sorted sperm) or its efficacy in young (nulliparous and primiparous) females.

Vitamin C attenuates negative effects of vitrification on sperm parameters, chromatin quality, apoptosis and acrosome reaction in neat and prepared normozoospermic samples

OBJECTIVE

Aim of this study was to evaluate the effects of vitamin C on sperm parameters, sperm chromatin quality and apoptosis resulted of vitrification in neat semen and prepared spermatozoa of normozoospermic samples.

MATERIAL AND METHODS

Forty semen samples from normozoospermic men were included in this prospective study. Each sample was divided into five groups. Group I: control or fresh semen, group II: semen prepared by swim-up method and then vitrified, group III: neat semen was vitrified, group IV: vitamin C (600 μM) was added to prepared spermatozoa and then vitrified and group V: vitamin C (600 μM) was added to neat semen and then vitrified. After warming, sperm analysis was done accordingly. For evaluating the sperm chromatin/DNA integrity status and acrosome reaction, we used toluidine blue (TB), acridine orange (AO), terminal transferase mediated deoxyuridine triphosphate biotin end labeling (TUNEL) and double staining tests.

RESULTS

All of the sperm parameters (count, motility, morphology and viability) had significant differences (P < 0.05) between different groups, especially in group IV. Data showed sperm chromatin damages and acrosome reaction abnormality increased resulted of vitrification, but, in the groups that added vitamin C (IV, V) rate of damages was decreased and this was notable in the group IV.

CONCLUSION

Vitamin C can attenuate the detrimental effects of vitrification on sperm parameters, chromatin quality and rate of apoptosis in both neat semen and prepared spermatozoa of normozoospermic samples.

Effects of chlorogenic acid and caffeic acid on the quality of frozen-thawed boar sperm

Chlorogenic acid (CGA) and caffeic acid (CA) are potent antioxidants that are mostly found in coffee beans. This study aimed to investigate the effects of CGA and CA supplementation during semen freezing on the quality of frozen-thawed boar spermatozoa. The antioxidants CGA and CA were added to a semen extender to achieve final concentrations of 50, 100, 200 and 400 µM. Supplementation of 100 µM CGA and CA yielded a significantly higher percentage of sperm viability (increased by 8%-10%) and plasma membrane integrity (increased by 4%-6%) than the control groups without the antioxidants at 0 and 3 hr after thawing (p < 0.05). At a concentration of 100 µM, CGA and CA also yielded beneficial effects on total and progressive sperm motility. Increases of CGA and CA concentrations to more than 200 µM did not enhance any sperm quality parameters. When the sperm penetrability and oocyte development by spermatozoa frozen with CGA and CA were evaluated, CGA and CA supplementations had no positive effects on the percentages of total fertilization, monospermic fertilization, cleavage and blastocyst formation. In conclusion, the supplementation of 100 µM CGA and CA during sperm freezing improved certain sperm parameters including motility, viability and plasma membrane integrity.

Effect of Astragalus polysaccharide addition to thawed boar sperm on in vitro fertilization and embryo development

It is important to utilize an antioxidant to ameliorate oxidative damage during boar sperm cryopreservation and thawing. Some studies have shown that Astragalus polysaccharide (APS) has antioxidant capabilities in sperm storage at low temperatures. However, the effects of APS on thawed sperm are unclear. In this study, the effect of supplementation of thawing boar semen extender with APS (0.5, 1, 5, 10 mg/mL) on sperm quality parameters (viability, motility, acrosome integrity and mitochondrial activity) was evaluated. Next, we investigated the effect of APS (0.5 mg/mL) supplementation on antioxidant parameters. Semen from two straws was thawed and diluted with three volumes of Beltsville Thawing Solution (BTS) and immediately divided into a control group without addition of antioxidants (CTR) and the APS group. Sperm and antioxidant parameters were evaluated in the CTR and APS groups after 1 h of incubation at 37 °C. Finally, we studied the effect of APS (0.5 mg/mL) supplementation on in vitro fertilization (IVF) and embryo development. The addition of different doses of APS to thawed sperm did not induce any significant effects on the sperm viability or motility compared to the sperm without APS treatment. However, the addition of 0.5 mg/mL APS to thawed sperm showed improved mitochondrial activity, higher penetration rate and increased total IVF efficiency compared with those of the control group. Moreover, our results indicate that the supplementation of APS in thawed sperm decreased the concentration of reactive oxygen species (ROS) and improved the activity of superoxide dismutase (SOD) and catalase (CAT). Finally, the addition of APS significantly increased the cleavage rate and blastocyst rate compared to those of the control group. In conclusion, the addition of APS to thawed boar sperm can enhance the antioxidant ability of sperm and improve in vitro fertilization (IVF) parameters and the outcomes of embryonic development. These results imply that APS has practical potential to enhance boar sperm reproductive performance.

Investigation of hydrostatic pressure-induced stress preconditioning of boar semen using modified cryopreservation

The aim of this study was to investigate the effect of varying hydrostatic pressure treatments (HP) on the boar semen quality during the modified cryopreservation. In Experiment I, combinations of pressure level (20/40/80 MPa) and duration of application (40/80/120 min) were used. Before freezing, only the magnitude but not the duration influenced the total (TM%) and progressive motilities (PM%). The 20/40 MPa levels yielded a significant (p < 0.05) improvement compared to control samples (atmospheric), but the 80 MPa was detrimental. The post-freezing-thawing (FT) motilities were influenced significantly by both the HP level and its duration. For TM%, the 40 MPa:120 min gave the highest post-FT result (54.8% ± 3.3%); however, the 40 MPa:80 min (41.0% ± 3.1%) application showed the largest and significant improvement (18.4% ± 3.1%) compared to its control (22.6% ± 3.1%) and compared to the improvement (12.9% ± 3.6%) achieved by 40 MPa:120 min. For PM%, the improvement with the 40 MPa:120 min application was slightly larger than with the 40 MPa:80 min one (15.2% ± 4.2% vs. 13.8% ± 3.3%); furthermore, the difference was not significant. In Experiment II, the 40 MPa:80 min combination was tested at four different stages of the semen handling. By pressurization after dilution with the freezing extender without glycerol, significantly higher post-FT values (TM%, intact acrosome% and head membrane%) were obtained. The two experiments demonstrated possible improvement in post-FT semen quality achievable through the appropriate application of HP to boar semen during cryopreservation.

Antioxidant supplementation, effect on post-thaw spermatozoan function in three sturgeon species

High levels of reactive oxygen species (ROS), which may be associated with reduced sperm quality, can be detected during cryopreservation of sperm of some species. Our objective was to investigate whether the addition of antioxidants to cryopreservation extenders influenced post-thaw sperm characteristics and fertility in Acipenser dabryanus, Acipenser sinensis and Acipenser baerii. Prior to freezing, sperm samples were diluted with a base extender as control or in extender supplemented with catalase (CAT), glutathione (GSH), cysteine (NAC), ascorbic acid (VC) or their paired combinations. Protective concentrations of CAT, GSH and VC in the three species were 25 U/ml, 0.25-0.5 mg/ml and 0.5 mg/ml, respectively. Cysteine showed no protective effect against ROS. The addition of CAT, GSH and VC positively affected either acrosome or membrane integrity of post-thawed sperm in the three species, as well as spermatozoan motility in A. sinensis. The combination of antioxidants did not show a positive synergistic effect. This study suggested that the use of antioxidants in the cryopreservation of sturgeon sperm has potential to decrease intracellular ROS, and consequently preserve acrosome and membrane integrity, as well as spermatozoan motility.

Fertility and flow cytometry study of frozen-thawed sperm in cryopreservation medium supplemented with soybean lecithin

Semen cryopreservation can provide genetic resources for a large number of females from a small number of superior males. Optimization of cryopreservation media to achieve the highest quality of post-thaw semen is crucial. Soybean lecithin has evaluated as a plant-based cryoprotectant for substitution of egg yolk in ram semen extender. Flow cytometric and fertility assessments were applied following cryopreservation procedure in two experimental groups (SL group: extender containing 1% w/v soybean lecithin and EY group: extender containing 20% v/v egg yolk). The higher percentage of live sperm and the lower percentage of dead sperm were obtained in SL (47.66 ± 1.38, 52.33 ± 1.69, respectively) extender compared to EY (41.16 ± 1.38, 58.83 ± 1.69). For motion characteristics, plasma membrane integrity, acrosome integrity and mitochondria activity, no significant difference was observed between SL and EY extenders. In artificial insemination experiment, there was no significant difference in pregnancy rate, lambing rate and twining rate between SL and EY extenders. It can be concluded that SL extender can be an efficient alternative extender to preserve ram sperm during cryopreservation procedure without adverse effects.

Preventive effect of Desferal on sperm motility and morphology

Transition metal ions, mainly iron, are involved in the generation of highly reactive hydroxyl radicals, which are the most powerful inducers of oxidative damage to all biomolecules. The lipids in sperm membranes are highly susceptible to oxidation. Sperm lipid peroxidation (LPO) leads to decrease of motility and reduction of likelihood for sperm-oocyte fusion. The excess radical production may affect also the spermatozoa morphology. The aim of the present study was to investigate the effect of Desferal on the LPO, motility, and morphology of boar sperm subjected to oxidative stress. After collection, the ejaculates were equally separated and diluted in a commercial semen extender (experiment 1) or in physiological saline (experiment 2). The ejaculates of the 2 experiments were divided into aliquots, which were incubated with one of the following agents: FeSO4 (0.1mM), H2 O2 (0.5mM), or FeSO4  + H2 O2 (Fenton system), in the presence or absence of Desferal. The application of Desferal in the incubation medium had a protective effect against FeSO4  + H2 O2 -induced sperm damage, namely, decrease of LPO; decrease the quantity of immotile spermatozoa and decrease the number of morphological abnormalities, regardless of the used medium. In experiment 2, the presence of FeSO4 in the incubation medium induced LPO in the same range as the combination FeSO4  + H2 O2 , in which the effect was reduced by Desferal. Thus, the supplement of Desferal to media used for sperm storage and processing could be a useful tool for diminishing oxidative injury and improving the quality of the semen.

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.

Stress preconditioning of semen before cryopreservation improves fertility and increases the number of offspring born: a prospective randomised study using a porcine model

The aim of the present study was to investigate the effect of applying sublethal stress treatment at room temperature, before cryopreservation (hydrostatic pressure (HP): 40 MPa, 80 min) of 34 boar ejaculate samples, on post-thawed motility and sow fertility. Sows (n = 102) were randomly allocated into equal groups inseminated with HP-treated or untreated frozen–thawed semen. Sows were inseminated twice, 10 h apart, with 6 × 109 spermatozoa per dose without oestrus synchronisation. Rates of non-return of oestrus and pregnancy, and total numbers of piglets and live piglets were significantly higher (P < 0.05) in the HP-treated group. There was also a numerical, albeit non-significant (P > 0.05), improvement in the farrowing rate in the HP-treated group. Although the number of live piglets per litter decreased approximately 15% in both groups by 42 days after farrowing, but this remained significantly higher in the HP-treated group. Although total and progressive sperm motility were significantly (P < 0.001) higher in the HP-treated group, there were no significant differences (P > 0.05) in these parameters between pregnant and non-pregnant sows in either group; thus motility can indicate, but not predict, improved fertility. In conclusion, HP treatment, with sperm cryopreservation, increases in vitro sperm motility and improves reproductive performance without adversely affecting the health of the piglets.

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.

Preincubation with green tea polyphenol extract is beneficial for attenuating sperm injury caused by freezing-thawing in swine

Polyphenols (PFs) extracted from green tea, known to be potent anti-oxidants, have been reported to be effective in increasing the motility and viability of mammalian sperm, preserved in a liquid form. Therefore, we tested whether PFs might also be effective for maintaining the integrity of frozen-thawed boar spermatozoa. Ejaculates, collected from Clawn miniature pigs, were diluted in a semen extender containing various amounts of PFs (0, 0.01, 0.05, 0.1 and 0.2% w/v) and then stored at 15°C overnight. The semen samples were processed, using the straw freezing procedure, and then frozen in liquid nitrogen. After rapid thawing at 40°C, the spermatozoa were subjected to several assays to evaluate semen quality. Spermatozoa frozen in a medium containing 0.01% w/v PFs exhibited significantly (P < 0.05) higher degrees of post-thawed viability and acrosomal integrity than those stored in the absence of PFs. However, no change in the mitochondrial activity was noted between the two groups. The inclusion of 0.01% PFs in the semen extender was significantly (P < 0.05) effective in increasing both the rates of monospermic oocyte formation and of blastocyst formation. These findings indicate that preincubation with the semen extender, containing 0.01% PFs prior to freezing, exerts a protective effect on boar sperm by preventing injuries associated with freezing-thawing.

The effect of extender, method of thawing, and duration of storage on in vitro fertility measures of frozen-thawed boar sperm

Frozen-thawed boar sperm (FTS) has reduced in vitro and in vivo life span compared to liquid semen. Experiments tested whether extenders, thawing procedures, and storage temperatures could extend the fertile life span of FTS. Experiment 1 tested the effect of six extenders on postthaw motility (MOT) and viability (VIA). Straws from boars (n = 6) were thawed, diluted into each extender, and evaluated at 20, 60, and 120 minutes. There was a trend (P = 0.08) for an extender-by-time interaction for MOT and effect of extender and time for MOT (P < 0.0001) and extender (P = 0.10) and time (P < 0.0001) for VIA. Experiment 2 evaluated the effect of temperature and time of thawing on in vitro fertility at intervals after thawing. Straws (0.5 mL) from different boar ejaculates (n = 15) were thawed at 50 °C for 10, 20, or 30 seconds or at 70 °C for 5, 10, or 20 seconds and evaluated at 5, 30, and 60 minutes. There was an effect of thawing treatment on MOT, VIA, and ACR (viable sperm with intact acrosomes, P < 0.0001) and an effect of time of evaluation (P < 0.0001) on MOT and ACR. Thawing at 70 °C for 20 seconds reduced (P < 0.05) MOT, VIA, and ACR compared to other treatments. Experiment 3 tested the effects of storage temperature and time after thawing using 20 ejaculates. Samples were thawed, diluted, and allotted to storage at 17 °C, 26 °C, or 37 °C with evaluation at 2, 6, 12, and 24 hours. There was a storage temperature and time effect and an interaction for MOT and VIA (P < 0.0001). Storage at 17 °C and 26 °C increased (P < 0.05) MOT over all times (38.5%) compared to 37 °C (26%), whereas MOT was reduced at intervals. Viability was also greatest with 17 °C and 26 °C compared to 37 °C and was also affected by time and decreased with time. These results indicate that FTS can be held at 17 °C or 26 °C for up to 2 hours before use and would allow for preparation of multiple doses. These data suggest in vitro fertility of FTS is affected by extenders, thawing, and storage.

Fertility of boar semen cryopreserved in extender supplemented with butylated hydroxytoluene

The present study was to determine the effect of butylated hydroxytoluene (BHT) on quality and fertilizing ability of frozen-thawed boar semen. In the first experiment, five crossbreds of Polish Landrace and Large White boars (five ejaculates per boar) were frozen in 0.5 mL straws after dilution with lactose-egg yolk-glycerol extender supplemented with 0 (control), 0.5, 1.0, and 2.0 mM BHT. The sperm quality was verified based on the motility (computer-assisted sperm analysis; total motility, %; progressive motility, %), membrane integrity (YO-PRO-1/propidium iodide [PI] assay), acrosome integrity (fluorescein isothiocyanate-conjugated with peanut agglutinin/PI), and lipid peroxidation (chemiluminescence method) at 15 minutes postthaw. In the second experiment, the semen cryopreserved in extender supplemented with 1.0 and 2.0 mM BHT were selected for intrauterine artificial insemination of synchronized gilts. An intrauterine artificial insemination with low numbers of spermatozoa (500 × 10(6)) was surgically infused into each uterine horn. The highest (P < 0.001) progressive motility (%), membrane integrity, and acrosomal integrity were noted by the addition of 1.0 and 2.0 mM BHT to the freezing extender. Moreover, the various concentrations (0.5-2.0 mM) of BHT caused a considerable decrease in lipid peroxidation in relation to the control extender (P < 0.001). The highest reproductive performance of inseminated gilts (farrowing rate, 86.7%; litter size, 10.8 ± 1.6) was observed when semen was cryopreserved in extender supplemented with 1.0 mM BHT. These findings demonstrate that the addition of 1.0 mM BHT to the freezing extender efficiently improves the fertilizing ability of postthaw boar spermatozoa.

Seminal plasma applied post-thawing affects boar sperm physiology: a flow cytometry study

Cryopreservation induces extensive biophysical and biochemical changes in the sperm. In the present study, we used flow cytometry to assess the capacitation-like status of frozen-thawed boar spermatozoa and its relationship with intracellular calcium, assessment of membrane fluidity, modification of thiol groups in plasma membrane proteins, reactive oxygen species (ROS) levels, viability, acrosomal status, and mitochondrial activity. This experiment was performed to verify the effect of adding seminal plasma on post-thaw sperm functions. To determine these effects after cryopreservation, frozen-thawed semen from seven boars was examined after supplementation with different concentrations of pooled seminal plasma (0%, 10%, and 50%) at various times of incubation from 0 to 4 hours. Incubation caused a decrease in membrane integrity and an increase in acrosomal damage, with small changes in other parameters (P > 0.05). Although 10% seminal plasma showed few differences with 0% (ROS increase at 4 hours, P < 0.05), 50% seminal plasma caused important changes. Membrane fluidity increased considerably from the beginning of the experiment, and ROS and free thiols in the cell surface increased by 2 hours of incubation. By the end of the experiment, viability decreased and acrosomal damage increased in the 50% seminal plasma samples. The addition of 50% of seminal plasma seems to modify the physiology of thawed boar spermatozoa, possibly through membrane changes and ROS increase. Although some effects were detrimental, the stimulatory effect of 50% seminal plasma could favor the performance of post-thawed boar semen, as showed in the field (García JC, Domínguez JC, Peña FJ, Alegre B, Gonzalez R, Castro MJ, Habing GG, Kirkwood RN. Thawing boar semen in the presence of seminal plasma: effects on sperm quality and fertility. Anim Reprod Sci 2010;119:160-5).

Emerging applications of sperm, embryo and somatic cell cryopreservation in maintenance, relocation and rederivation of swine genetics

Advances in porcine assisted reproductive technology (ART) make it possible to use cryopreserved sperm, embryos and somatic cells in the maintenance, relocation and regeneration of swine genetics. In this review, development of key application-limiting technology is discussed in each cell type, focusing on the efficiencies, ease of storage and transportation, and minimization of pathogen transmission. Methods to regenerate swine genetics and/or models using frozen sperm, embryos and somatic cells in combination with other porcine ARTs, such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and somatic cell nuclear transplantation (SCNT), are also discussed. The applications of these ARTs utilizing cryopreserved cells will greatly increase the efficiency as well as biosecurity for maintenance, relocation and rederivation of swine genetics/models.

Detrimental effects of non-functional spermatozoa on the freezability of functional spermatozoa from boar ejaculate

In the present study, the impact of non-functional spermatozoa on the cryopreservation success of functional boar spermatozoa was evaluated. Fifteen sperm-rich ejaculate fractions collected from five fertile boars were frozen with different proportions of induced non-functional sperm (0--native semen sample-, 25, 50 and 75% non-functional spermatozoa). After thawing, the recovery of motile and viable spermatozoa was assessed, and the functional of the spermatozoa was evaluated from plasma membrane fluidity and intracellular reactive oxygen species (ROS) generation upon exposure to capacitation conditions. In addition, the lipid peroxidation of the plasma membrane was assessed by the indirect measurement of malondialdehyde (MDA) generation. The normalized (with respect to a native semen sample) sperm motility (assessed by CASA) and viability (cytometrically assessed after staining with Hoechst 33342, propidium iodide and fluorescein-conjugated peanut agglutinin) decreased (p<0.01) as the proportion of functional spermatozoa in the semen samples before freezing decreased, irrespective of the semen donor. However, the magnitude of the effect differed (p<0.01) among boars. Moreover, semen samples with the largest non-functional sperm subpopulation before freezing showed the highest (p<0.01) levels of MDA after thawing. The thawed viable spermatozoa of semen samples with a high proportion of non-functional spermatozoa before freezing were also functionally different from those of samples with a low proportion of non-functional spermatozoa. These differences consisted of higher (p<0.01) levels of intracellular ROS generation (assessed with 5-(and-6) chloromethyl-20,70-dichlorodihydrofluorescein diacetate acetyl ester; CM-H(2)DCFDA) and increased (p<0.01) membrane fluidity (assessed with Merocyanine 540). These findings indicate that non-functional spermatozoa in the semen samples before freezing negatively influence the freezability of functional spermatozoa.

Effect of the addition of beta-mercaptoethanol to a thawing solution supplemented with caffeine on the function of frozen-thawed boar sperm and on the fertility of sows after artificial insemination

We have reported that artificial insemination (AI) with frozen-thawed boar semen supplemented with caffeine increased the number of uterine sperm by inhibiting the migration of polymorphonuclear leukocytes (PMNs) into the uterine lumen, thereby improving the fertility of gilts and sows. The objective of the present study was to examine the effects of the addition of the antioxidant beta-mercaptoethanol (bME) and caffeine to the thawing solution on the function of frozen-thawed sperm, on the phagocytic activity of PMNs for sperm, and on the fertility of sows after AI. When frozen-thawed sperm were cultured in the presence of 25 or 50 μm bME, sperm capacitation and spontaneous acrosome reactions were inhibited (P < 0.01). There was no effect of bME on phagocytic activity of PMNs for sperm in vitro. When hormonally treated (400 IU of equine chorionic gonadotropin + 200 IU of human chorionic gonadotropin) weaned sows experienced a single intrauterine insemination with frozen-thawed sperm (25 × 10(8) sperm per 50 ml dose) 40 h after subsequent hCG administration, pregnancy and farrowing rates were unaffected by the addition of 50 μm bME (pregnancy rate, 20 vs 21% in controls; farrowing rate, 20 vs 21%; n = 15 and 14, respectively). However, litter size tended to be higher than in the presence of 50 μm bME compared to its absence (10.0 ± 1.0 vs 5.7 ± 1.5, respectively; P < 0.07). Thus, the addition of bME to the thawing solution containing caffeine could be of benefit for improving the function of frozen-thawed sperm without influencing the phagocytic activity of PMNs for sperm. Although there were no statistically significant effects of bME on pregnancy or farrowing rates, the litter size tended to be higher in the sows subjected to a fixed-time single AI treatment with synchronized ovulation.

The role of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in comparison with whole egg yolk for sperm cryopreservation in rhesus monkeys

Low-density lipoprotein (LDL) extracted from hen egg yolk has recently been considered to be superior to whole egg yolk in sperm cryopreservation of various animal species. Meanwhile, there was a notion that high-density lipoprotein (HDL) in egg yolk may have a negative effect on post-thaw survival. The role of LDL and HDL in sperm cryopreservation of rhesus monkeys has not been explored. The present study evaluates their effect in comparison with egg yolk with or without the addition of permeable cryoprotectant (glycerol) on sperm cryopreservation of rhesus macaques. In addition, various additives intended to change the lipid composition of LDL-sperm membrane complex have also been tested for their effectiveness in preserving post-thaw viability. Our findings indicated that LDL is the main component in egg yolk that is responsible for its protective role for sperm cryopreservation in rhesus monkeys. Regardless of the presence or absence of glycerol, the protective role of LDL is similar to that of egg yolk and we did not observe any superiority in post-thaw survival with LDL when compared to egg yolk. Modifying the lipid composition of LDL-sperm membrane complex with the addition of cholesterol, cholesterol loaded cyclodextrin and phosphatidylcholine also did not yield any improvements in post-thaw survival; while addition of methyl-β-cyclodextrin reduced post-thaw motility. HDL plays a neutral role in sperm cryopreservation of rhesus monkeys. The present study suggests that egg yolk may still hold advantages when compared with LDL as effective components in extenders for sperm cryopreservation in rhesus monkeys.

Changes in sperm membrane and ROS following cryopreservation of liquid boar semen stored at 15 °C

Boar semen is occasionally transferred to different locations in liquid form at 15 °C for cryopreservation. However, the use of frozen boar semen is limited due to the high susceptibility of boar sperm to cold shock. The aim of this study was to help improve the quality of frozen boar semen by determining the changes in sperm membrane and ROS during the cryopreservation processes of 15 °C-stored boar semen. Semen was collected from ten Duroc boars and transferred to our laboratory in liquid form stored at 15 °C. After cooling to 5 °C and freezing-thawing, conventional sperm parameters (total motility, progressive motility, and normal morphology), plasma membrane integrity, acrosomal membrane status, and intracellular ROS were evaluated. Sperm function, as assessed by conventional parameters, was unaffected by cooling but was decreased by freezing-thawing (P<0.05). However, the cooling and freezing-thawing processes led to damages in the sperm plasma membrane, and the cooling process caused increase in mean PNA (peanut agglutinin)-fluorescence intensity in viable acrosome-intact sperm (P<0.05). In ROS evaluation, the cooling process decreased intracellular (·)O(2) and H(2)O(2) in viable sperm (P<0.05), while the freezing-thawing process increased intracellular H(2)O(2) (P<0.05) without change in intracellular (·)O(2) in viable sperm. Our results suggest that, in liquid boar semen stored at 15 °C, cooling may be primarily responsible for the destabilization of sperm membranes in viable sperm, while freezing-thawing may induce reductions in sperm function with increase in membrane damage and H(2)O(2).

Antioxidants, Oxyrase, and mitochondrial uncoupler 2,4-dinitrophenol improved postthaw survival of rhesus monkey sperm from ejaculates with low cryosurvival

Various antioxidant strategies such as supplementation of antioxidants, limiting oxygen concentration with Oxyrase, and reducing reactive oxygen species through mild mitochondrial uncoupling had statistically significant beneficial effects on sperm cryopreservation from rhesus monkeys with low cryoresistant ejaculates. Individuals or species that have higher sensitivity to cryodamage may derive the most benefit from these treatments.

Fertility after post-cervical artificial insemination with cryopreserved sperm from boar ejaculates of good and poor freezability

This study compared the field fertility outcomes in frozen-thawed (FT) sperm from boar ejaculates with different freezability (good, GFE/poor, PFE) while testing the reliability of the post-cervical artificial insemination (post-CAI) in FT sperm. The assay was conducted over eight months with 86 weaned sows being inseminated by post-CAI. Every ejaculate in a total of 26 from 15 Piétrain boars was divided into a refrigerated semen portion (FS; control treatment) and a cryopreserved portion (FT sperm), and the ejaculates were in turn classified as GFE or PFE in function of the sperm progressive motility and viability at 240min post-thaw. As result, one of four possible treatments was randomly given to each sow: FS-GFE, FS-PFE, FT-GFE and FT-PFE. The number of pregnant and farrowing sows in FT-GFE did not significantly differ from those of FS control treatments. Contrarily, the probabilities of pregnancy were two times lower after inseminations with FT-PFE (P<0.05) compared to FT-GFE, which indicates that ejaculates with high post-thaw sperm progressive motility and viability are more likely to result in pregnancies than those with poor in vitro sperm function. There were no differences in litter size or the risk of backflow among treatments. Further trials are required to determine the optimal volume and concentration of FT sperm in post-CAI to obtain a more reliable method for farmers interested in cryopreserved sperm.