A comparison of BoviPure and Percoll on bull sperm separation protocols for IVF

Glycerol is not suitable for the cryopreservation of quail semen

1. This study investigated the potential use of glycerol as a cryoprotectant for quail sperm cells. Its role in maintaining sperm fertilising ability in vivo and in vitro quality parameters, such as motility, was assessed.2. The data showed that the presence of glycerol in semen samples was associated with infertility, which suggested that removal prior to insemination is mandatory. Removal through serial dilution centrifugation was associated with fewer than 5% of motile sperm cells and resulted in no fertility.3. In conclusion, glycerol alone is not suitable for quail semen cryopreservation, and other approaches need to be investigated to develop cryobanking programmes for this species.

Filtration techniques are advantageous over colloidal centrifugation in improving freezability of low-quality buffalo bull (Bubalus bubalis) ejaculates

The study compared efficacy of three sperm selection techniques in improving freezability of low-quality Murrah buffalo bull ejaculates. Sephadex (SEP), Sephadex ion-exchange filtration (SIE), and 40/80% BoviPure™ (BP) gradient centrifugation protocols were standardized (ejaculates, n = 24). In Experiment-I, Sephadex G-75, G-100, and combined Sephadex G (75-100) column filtrates were compared. In Experiment-II, BP protocols: 200 g-10 min, 250 g-5, and 10 min, 300 g-10, and 15 min were compared. In fresh semen, Sephadex G (75-100) filtration and 250 g-5 min BP protocol improved sperm functions and were used in Experiment-III, where SEP G (75-100), SIE G (75-100), and 250 g-5 min BP processed ejaculates (n = 48) were cryopreserved and compared at post-thaw stage. The mean recovery rate differed in order: SEP > SIE > BP. SIE filtration significantly improved progressive motility, livability, membrane integrity, bovine cervical mucus penetration and live non-apoptotic sperm. Compared with control, all three techniques equally reduced post-dilution and post-thaw lipid peroxidation (LPO) rate. SEP post-thaw filtrates observed lower cryocapacitation-like changes, LPO (C11-BODIPY581/591), and higher active mitochondria than other treatments. SIE and SEP equally improved post-thaw acrosome-intact sperm over BP. Filtration techniques, preferably, Sephadex ion-exchange filtration can most efficiently process low-quality buffalo bull ejaculates for cryopreservation and improve freezability.

Pre-freezing selection of Holstein bull semen with the BoviPure colloid as double- or single-layer centrifugation improves the post-thawing quality

Artificial insemination (AI) is critical for breeding in the dairy industry. High-merit bulls can present low freezability, hampering genetic dissemination. Thawed semen can be improved using density gradient centrifugation (DGC) with colloids, but little information deals with the pre-freezing application. Thus, the BoviPure colloid (optimized for bull spermatozoa) was tested for pre-freezing application as the usual double-layer (DLC) versus single-layer (SLC, quick and economical). Semen from twelve Holstein-Friesian bulls was extended with OPTIXcell extender, frozen (Control), or processed by SLC or DLC and frozen. Sperm were assessed pre-freezing for motility and viability and post-thawing (directly and after 4 h 38 °C) for apoptosis, capacitation status, acrosomal damage, mitochondrial activity, cytoplasmic and mitochondrial reactive oxygen species (ROS), and chromatin status (SCSA for DNA fragmentation and chromatin compaction and monobromobimane, mBBr, for disulfide bridges evaluation). The DGC improved parameters post-thawing (e.g., 57.5%±10.1 motility vs. control 53.3% ± 11.2) at the cost of sperm loss (sperm recovery of DGC 14.4% ± 2.5 and SLC 17.4% ± 2.5). DNA fragmentation (%DFI) decreased (0.21% ± 0.53 vs. control 1.30% ± 0.10), and SLC reduced chromatin compaction. A clustering procedure separated lesser (LF) and greater freezability (GF) bulls. LF samples were especially benefited by DGC, with SLC providing better post-thawing results for this group. In conclusion, pre-freezing DGC improved sperm parameters post-thawing, potentially improving the cryopreservation of low-freezability semen from high-merit bulls. SLC, quicker and economical, would be preferable since it showed similar or higher performance than DLC.

Evaluation of a novel microfluidic chip-like device for purifying bovine frozen-thawed semen for in vitro fertilization

The aim of this study was to validate a novel sperm purification device, the VetCount™ Harvester, for use in bovine in vitro fertilization (IVF). The device's performance was compared to BoviPure™ gradient centrifugation, a commercially available and accepted routine technique. Semen quality parameters were assessed for frozen-thawed semen from six different bulls (n = 6) following sperm purification. For each bull two semen subsamples were purified utilizing BoviPure™ gradient centrifugation and the VetCount™ Harvester, including a third subsample as untreated control. Both treatments significantly increased the proportion of progressively motile sperm cells (84.4 ± 14.1% and 85.1 ± 7.8%, respectively) compared to the untreated semen (41.9 ± 18.8%). BoviPure™ gradient and VetCount™ Harvester selected predominantly viable acrosome intact (VAI) sperm cells with low membrane fluidity and low free intracellular calcium concentration [Ca2+]i (76.5 ± 4.4% and 78.6 ± 6.0%). Normalizing [Ca2+]i of VAI sperm cells (non-treated semen: [Ca2+]i = 1) VetCount™ Harvester purified spermatozoa (0.67 ± 0.10) showed significantly lower [Ca2+]i than BoviPure™ treated sperm (0.84 ± 0.14; P < 0.05). Subsequently, the fertilizing ability of the spermatozoa was evaluated performing a competitive fertilization assay. Sperm cells from both treatment groups were fluorescently labelled using different dyes and added in equal amounts to in vitro matured oocytes. After 18 h co-incubation, the origin of the fertilizing sperm cell was evaluated via fluorescence microscopy. In two bulls, VetCount™ Harvester selected sperm that fertilized significantly more oocytes then BoviPure™ treated sperm, in another bull it was the opposite. For three bulls no difference was observed. We conclude that the VetCount™ Harvester selects a high-quality, fertile sperm fraction from frozen-thawed bull semen. However, some considerations have to be kept in mind for the direct use of the isolated sperm fraction in IVF.

The influence of Percoll® density gradient centrifugation before cryopreservation on the quality of frozen wisent (Bison bonasus) epididymal spermatozoa

Background

The wisent (Bison bonasus) is a species that has undergone a population bottleneck. Homozygosity is prevalent within the population and may have a negative impact on semen quality in wisent bulls. Semen samples containing a large amount of functionally and morphologically impaired or dead spermatozoa have lower tolerance for cryopreservation process. Such samples are prone to involve damage acrosomes, to produce and release reactive oxygen which negatively affects proper function of spermatozoas. It is a good practice to select intact and viable gametes before subjecting the sample to cryopreservation to improve the efficiency of this process. The aim of this study was to assess the ability of Percoll® density gradient centrifugation in order to improve the quality of wisent spermatozoa after cryopreservation. Spermatozoa samples were analysed with computer-assisted semen analysis system and flow cytometry.

Results

Percoll® density gradient centrifugation resulted in increased percentage of motile spermatozoa, higher proportion of spermatozoa with normal morphology and proper functionality but also in a significant reduction of the total number of gametes. Nevertheless, the concentration of frozen spermatoza was still sufficient for obtaining a few complete insemination doses suggested for cattle from each epididymis.

Conclusions

While creating a high-quality genetic reserve, for in vitro fertilisation purposes, eliminating detritus and improving the overall quality of samples is more important than total number of spermatozoa. For these reasons, the achievement of higher post thaw quality of spermatozoa justifies the purification of samples by centrifugation in a Percoll® density gradient prior to the cryopreservation process.

A Review on Microfluidics: An Aid to Assisted Reproductive Technology

Infertility is a state of the male or female reproductive system that is defined as the failure to achieve pregnancy even after 12 or more months of regular unprotected sexual intercourse. Assisted reproductive technology (ART) plays a crucial role in addressing infertility. Various ART are now available for infertile couples. Fertilization in vitro (IVF), intracytoplasmic sperm injection (ICSI) and intrauterine insemination (IUI) are the most common techniques in this regard. Various microfluidic technologies can incorporate various ART procedures such as embryo and gamete (sperm and oocyte) analysis, sorting, manipulation, culture and monitoring. Hence, this review intends to summarize the current knowledge about the application of this approach towards cell biology to enhance ART.

Lipid peroxidation in bull semen influences sperm traits and oxidative potential of Percoll®-selected sperm

Although bovine embryo in vitro production (IVP) is a common assisted reproductive technology, critical points warrant further study, including sperm traits and oxidative status of sperm for in vitro fertilization (IVF). Our aim was to evaluate whether the lipid peroxidation index of commercial bull semen is influenced by sperm traits and oxidative status of sperm populations selected using Percoll® gradient. Semen straws from 48 batches from 14 Nelore bulls were thawed individually, analyzed for motility and subjected to Percoll selection. After Percoll, the lipid peroxidation index of the extender was evaluated, whereas selected sperm were analyzed for motility, acrosome and membrane integrity, mitochondrial membrane potential, chromatin resistance and oxidative potential under IVF conditions. Batches were divided retrospectively in four groups according to lipid peroxidation index. Sperm from Group 4 with the lowest index of lipid peroxidation had, after Percoll selection, greater plasma membrane integrity (81.3%; P = 0.004), higher mitochondrial potential (81.1%; P = 0.009) and lower oxidative potential (135.3 ng thiobarbituric acid reactive substances (TBARS)/ml; P = 0.026) compared with Group 1 with highest lipid peroxidation index (74.3%, 73% and 213.1 ng TBARS/ml, respectively). Furthermore, we observed negative correlations for the lipid peroxidation index with motility, membrane integrity and mitochondrial potential, and positive correlations with oxidative potential. In conclusion, oxidative stress in semen straws, as determined using lipid peroxidation in the extender, is associated with sperm traits and their oxidative potential under IVF conditions. These results provided further insights regarding the importance of preventing oxidative stress during semen handling and cryopreservation, as this could affect sperm selected for IVF. Finally, Percoll selection did not completely remove sperm with oxidative markers.

A novel microfluidic chip-based sperm-sorting device constructed using design of experiment method

Microfluidics is proposed as a technique for efficient sperm sorting, to achieve the ultimate goal of resolving infertility problems in livestock industry. Our study aimed to design a microfluidic sperm-sorting device (SSD) through a high-efficacy and cost- and time-effective fabrication process, by using COMSOL Multiphysics simulation and modeling software, and the design of experiment (DOE) method. The eight factors affecting SSD performance were established. The simulation was then run, and statistically significant factors were analyzed. Minitab16 was used to optimize the design modulus factor. By setting the statistical significance at p < 0.05, the factors affecting experimental structure were analyzed. At a desirability of 97.99, the optimal parameters for the microfluidic chip were: angle between sperm and medium inlet chambers (A = 43°), sperm inlet flow rate (B = 0.24 µL min^-1), medium inlet flow rate (C = 0.34 µL min^-1), and inlet and outlet chamber lengths (D = 5000 µm). These optima were then applied to microfluidics device construction. The device was produced using soft lithographic microfabrication techniques and tested on Holstein-Friesian bull sperm. The highest bull sperm-sorting performance for this microfluidic device prototype was 96%. The error between the simulation and the actual microfluidic device was 2.72%. Fluid viscosity ranges analysis-based simulations revealed acceptable fluid viscosity tolerances for the SSD. The simulation results revealed that the acceptable tolerance range for fluid viscosity was 0.00001-0.003 kg m^-1 s^-1. This optimally designed microfluidic chip-based SSD may be integrated into sperm x/y separation micro devices.

Effect of using frozen-thawed bovine semen contaminated with lumpy skin disease virus on in vitro embryo production

Lumpy skin disease (LSD) is an important transboundary animal disease of cattle with significant economic impact because of the implications for international trade in live animals and animal products. LSD is caused by a Capripoxvirus, LSD virus (LSDV), and results in extensive hide and udder damage, fever and pneumonia. LSDV can be shed in semen of infected bulls for prolonged periods and transmitted venereally to cows at high doses. This study examined the effects of LSDV in frozen-thawed semen on in vitro embryo production parameters, including viral status of media and resulting embryos. Bovine oocytes were harvested from abattoir-collected ovaries and split into three experimental groups. After maturation, the oocytes were fertilized in vitro with frozen-thawed semen spiked with a high (HD) or a lower (LD) dose of LSDV, or with LSDV-free semen (control). Following day 7 and day 8 blastocyst evaluation, PCR and virus isolation were performed on all embryonic structures. After completing sufficient replicates to reach 1,000 inseminated oocytes, further in vitro fertilization (IVF) runs were performed to provide material for electron microscopy (EM) and embryo washing procedures. Overall, in vitro embryo yield was significantly reduced by the presence of LSDV in frozen-thawed semen, irrespective of viral dose. When semen with a lower viral dose was used, significantly lower oocyte cleavage rates were observed. LSDV could be detected in fertilization media and all embryo structures, when higher doses of LSDV were present in the frozen-thawed semen used for IVF. Electron microscopy demonstrated LSDV virions inside blastocysts. Following the International Embryo Transfer Society washing procedure resulted in embryos free of viral DNA; however, this may be attributable to a sampling dilution effect and should be interpreted with caution. Further research is required to better quantify the risk of LSDV transmission via assisted reproductive procedures.

3D imaging of sex-sorted bovine spermatozoon locomotion, head spin and flagellum beating

With the advent of sperm sex sorting methods and computer-aided sperm analysis platforms, comparative 2D motility studies showed that there is no significant difference in the swimming speeds of X-sorted and Y-sorted sperm cells, clarifying earlier misconceptions. However, other differences in their swimming dynamics might have been undetectable as conventional optical microscopes are limited in revealing the complete 3D motion of free-swimming sperm cells, due to poor depth resolution and the trade-off between field-of-view and spatial resolution. Using a dual-view on-chip holographic microscope, we acquired the full 3D locomotion of 235X-sorted and 289 Y-sorted bovine sperms, precisely revealing their 3D translational head motion and the angular velocity of their head spin as well as the 3D flagellar motion. Our results confirmed that various motility parameters remain similar between X- and Y-sorted sperm populations; however, we found out that there is a statistically significant difference in Y-sorted bovine sperms' preference for helix-shaped 3D swimming trajectories, also exhibiting an increased linearity compared to X-sorted sperms. Further research on e.g., the differences in the kinematic response of X-sorted and Y-sorted sperm cells to the surrounding chemicals and ions might shed more light on the origins of these results.

A technical assessment of the porcine ejaculated spermatozoa for a sperm-specific RNA-seq analysis

The study of the boar sperm transcriptome by RNA-seq can provide relevant information on sperm quality and fertility and might contribute to animal breeding strategies. However, the analysis of the spermatozoa RNA is challenging as these cells harbor very low amounts of highly fragmented RNA, and the ejaculates also contain other cell types with larger amounts of non-fragmented RNA. Here, we describe a strategy for a successful boar sperm purification, RNA extraction and RNA-seq library preparation. Using these approaches our objectives were: (i) to evaluate the sperm recovery rate (SRR) after boar spermatozoa purification by density centrifugation using the non-porcine-specific commercial reagent BoviPure^TM; (ii) to assess the correlation between SRR and sperm quality characteristics; (iii) to evaluate the relationship between sperm cell RNA load and sperm quality traits and (iv) to compare different library preparation kits for both total RNA-seq (SMARTer Universal Low Input RNA and TruSeq RNA Library Prep kit) and small RNA-seq (NEBNext Small RNA and TailorMix miRNA Sample Prep v2) for high-throughput sequencing. Our results show that pig SRR (~22%) is lower than in other mammalian species and that it is not significantly dependent of the sperm quality parameters analyzed in our study. Moreover, no relationship between the RNA yield per sperm cell and sperm phenotypes was found. We compared a RNA-seq library preparation kit optimized for low amounts of fragmented RNA with a standard kit designed for high amount and quality of input RNA and found that for sperm, a protocol designed to work on low-quality RNA is essential. We also compared two small RNA-seq kits and did not find substantial differences in their performance. We propose the methodological workflow described for the RNA-seq screening of the boar spermatozoa transcriptome.

ABBREVIATIONS

FPKM: fragments per kilobase of transcript per million mapped reads; KRT1: keratin 1; miRNA: micro-RNA; miscRNA: miscellaneous RNA; Mt rRNA: mitochondrial ribosomal RNA; Mt tRNA: mitochondrial transference RNA; OAZ3: ornithine decarboxylase antizyme 3; ORT: osmotic resistance test; piRNA: Piwi-interacting RNA; PRM1: protamine 1; PTPRC: protein tyrosine phosphatase receptor type C; rRNA: ribosomal RNA; snoRNA: small nucleolar RNA; snRNA: small nuclear RNA; SRR: sperm recovery rate; tRNA: transfer RNA.

Sephadex filtration as successful alternative to density-gradient centrifugation procedures for ram sperm selection with improved kinetics

Density-gradients centrifugation (DGC) and filtration columns (FC) are used to separate deformed or dead sperm, debris, and other cells that may negatively affect the fertilizing capacity of sperm in fresh, chilled and frozen/thawed semen. The present study was conducted to evaluate the suitability of DGC (BoviPure®, Percoll® and Accudenz®) and FC (Sephadex G-15®) sperm selection procedures for fresh-extended and cold-stored ram semen by assessment of post-treatment sperm quality variables. Twenty normospermic ejaculates from ten adult Merino rams were used. Sperm concentration of recovered cells was greater (P < 0.001) after BoviPure treatment than other procedures in both fresh and cold semen. With the Sephadex method, there were more desirable values than with use of DGC procedures in several sperm motility variables measured by using the CASA system. In non-refrigerated semen samples, the percentage of progressive sperm motility (%PSM) after Sephadex filtration was greater (P < 0.05) than after BoviPure treatment; the straightline velocity (VSL) value after Sephadex filtration was greater (P < 0.01) than after Accudenz treatment; the amplitude of lateral head displacement (ALH) after Sephadex and Accudenz treatment was less than non-filtered semen (P < 0.001) and after Percoll (P < 0.01) and BoviPure (P < 0.05) treatments. In cold-stored semen samples, the %PSM after Sephadex filtration was greater than non-filtered (P < 0.05) semen and after BoviPure (P < 0.05), Percoll (P < 0.05) and Accudenz (P < 0.001) treatments. It is concluded that Sephadex column filtration can be used to select ram sperm in non-refrigerated and cooled semen, because percentage progressively motile sperm and some other sperm motility characteristics are greater with use of this techniques as compared with use of DGC methods.

Exogenous melatonin influences distribution of French Alpine buck spermatozoa in morphometrically distinct subpopulations during the non-breeding season

The aim of this study was to establish subpopulations of spermatozoa in bucks using the principal component (PC) and cluster analysis according to morphometric head and tail variables, and to determine differences in proportions of subpopulations between exogenous melatonin-treated and control bucks. The bucks (n = 12) were assigned to two groups comprising six bucks each. By the end of March, four melatonin implants were inserted in the bucks in the experimental group. Semen was collected weekly using an artificial vagina from March to May (the non-breeding season). Analyses were performed in stained smears by SFORM computer-assisted program for eight head and five tail variables. The PC analysis revealed four components with the most important value for each (head outline, head ellipticity, mid-piece length and width). Cluster analysis indicated there were three subpopulations (average-sized spermatozoa- C_1; small and less-elliptic - C_2; big and elliptic - C_3). Melatonin-treated bucks had a greater proportion of C_1 spermatozoa and a lesser proportion of C_2 spermatozoa during May (P < 0.05). To the best of our knowledge, this is the first study where PC and cluster analyses were performed on buck semen with head and tail variables analyzed together, in the same analysis, to evaluate spermatozoa population. Also, this is the first analysis of morphometric variables for assessing the influence of melatonin on spermatozoa subpopulations. The positive effect of melatonin on the proportions of spermatozoa in subpopulations could have been a consequence of the decreasing the proportion of the subpopulation with the least head and tail sizes and ellipticity.

Sperm preparation through Sephadex™ filtration improves in vitro fertilization rate of buffalo oocytes

Routinely, swim-up method is used to separate high-quality sperm; however, long processing time and close cell-to-cell contact during the centrifugation step are inevitable elements of oxidative stress to sperm. The objective was to evaluate Sephadex^™ and glass wool filtration to separate motile, intact and viable sperm for in vitro fertilization in buffalo. The cumulus-oocyte complexes (COCs) were collected from ovaries of slaughtered buffaloes by aspiration and matured for 24 hr in CO₂ incubator at 38.5°C and 5% CO₂ . Matured COCs were rinsed twice in fertilization TALP and placed in the pre-warmed fertilization medium without sperm. Cryopreserved buffalo semen was thawed at 37°C for 30 s and processed through Sephadex^™ , glass wool filtration and swim-up (control). Total and motile sperm recovery rates were assessed, resuspended in fertilization TALP and incubated for 15-20 min in CO₂ incubator. Samples prepared by each method were divided into two aliquots: one aliquot was studied for sperm quality (progressive motility, membrane integrity, viability, liveability), while the other was subjected to co-incubation with sets of 10-15 in vitro matured oocytes. Data on sperm quality were analysed by ANOVA, while in vitro fertilizing rates were compared by chi-squared test using SPSS-20. Least significant difference (LSD) test was used to compare treatment means. Glass wool filtration yielded higher total and motile sperm recovery rate, while Sephadex^™ filtration improved (p < .05) sperm quality (progressive motility, membrane integrity, viability, liveability). Sperm preparation through Sephadex filtration yielded higher in vitro fertilization rate in terms of cleavage rate compared to glass wool filtration and swim-up (control). In conclusion, cryopreserved Nili-Ravi buffalo sperm selected through Sephadex filtration showed improved quality and yielded better fertilization rates (cleavage rate) of in vitro matured/fertilized oocytes. Sephadex filtration could be a promising technique for use in in vitro fertilization in buffalo.

Gradient sperm selection for reproductive techniques in cattle: Is Isolate a suitable replacement for Percoll?

In assisted reproductive techniques, it is essential to perform a sperm selection to obtain spermatozoa with high motility and membrane integrity for in vitro fertilisation (IVF) and high-DNA integrity for intracytoplasmic sperm injection (ICSI). In this study, we evaluated whether Isolate^® was a suitable substitute for Percoll^® for assisted reproductive techniques. Commercial cryopreserved bovine semen was used after selection in both gradients, and plasma and acrosome membrane integrity, reactive oxygen species (ROS) levels, DNA integrity and mitochondrial membrane potential (ΔΨm) were assessed by flow cytometry. Motility parameters were also evaluated by CASA system. A similar percentage of spermatozoa with intact plasma membrane, acrosome integrity and high ΔΨm was observed in both sperm selection methods, but only Percoll^® showed higher percentage of spermatozoa with intact plasma and acrosome membrane compared to the post-thawing group. No differences were observed in the motility, ROS, DNA fragmentation and on the in vitro embryo production in all experimental groups. In conclusion, the selection of bovine spermatozoa with Isolate^® generates spermatozoa with similar quality parameters and embryonic development compared to Percoll^® providing a suitable alternative sperm selection method for assisted reproductive techniques in this species.

Effect of different mini-volume colloid centrifugation configurations on flow cytometrically sorted sperm recovery efficiency and quality using a computer-assisted semen analyzer

Straws of sex-sorted sperm are usually packaged at a low concentration (e.g., ~2.1 × 10⁶  sperm/ml) and cost significantly more than unsorted conventional semen from the same sire. In order to maximize the efficiency of using sex-sorted sperm under in vitro fertilization conditions, the selection of an appropriate sperm separation technique is essential. In this study, the effect of using different silane-coated silica colloid dilutions and layering configurations during centrifugation of sex-sorted sperm was examined over an extended period of incubation time. Sperm recovery and viability after centrifugation using the colloid separation technique were measured along with several sperm motility parameters using CASA. For this purpose, frozen and thawed sex-sorted sperm samples were centrifuged using mini-volume single-layer (40%, 60% and 80%) and mini-volume two-layer (45%/90%, 40%/80% and 30%/60%) separation configurations using PureSperm^® . A single layer of 40% PureSperm^® recovered significantly more sex-sorted sperm (78.07% ± 2.28%) followed by a single layer of 80% PureSperm^® (68.43% ± 2.33%). The lowest sperm recovery was obtained using a two-layer PureSperm^® dilution of 45%/90% (47.57% ± 2.33%). Single-layer centrifugation recovered more sorted sperm (68.67% ± 1.74%) than two layer (53.74% ± 1.74%) (p < .0001). A single layer of 80% PureSperm^® exhibited the highest sorted sperm viability (72.01% ± 2.90%) after centrifugation (p < .05). The mini-volume single layer of 80% PureSperm^® was determined to be an effective alternative to a two-layer centrifugation configuration for sex-sorted sperm selection. In addition, single-layer colloid dilution of 80% performed either as well as or significantly outperformed the other treatments, as well as the control, with regard to motility (MOT) for all time periods of analysis.

Sperm membrane integrity and stability after selection of cryopreserved ovine semen on colloidal solutions

The aim of this study was to evaluate the effect of four methods of sperm selection, on the integrity and stability of the plasma membrane, integrity of the acrosomal membrane and spermatic morphology in frozen/thawed ovine semen. Two types of colloidal silica: colloidal silica-silane and colloidal silica-polyvinylpyrrolidone (PVP), and two aliquots: 1 and 4 ml, were used for sperm selection. Probes FITC-PSA and PI were used to measure the integrity of the plasma and acrosomal membranes. Plasma membrane stability was measured, using fluorescent probes M540 and YOPRO1. Effective reduction in the incidence of spermatozoa with acrosomal pathologies was only achieved using 1 ml colloidal silica-silane. All methods were efficient in select viable and unreacted spermatozoa. Only methods using 1 ml of silica were efficient in decrease spermatozoa stained by PI (death). Methods using silica colloidal-silane were more efficient to decrease apoptotic cells after selection when compared to silica colloidal-PVP. In conclusion, sperm selection in colloidal silica-silane and colloidal silica-PVP improved sperm quality when compared to the controls. The method using 1 ml of colloidal silica-silane is the preferred method because its effectiveness and lower cost.

Bull Fertility and Its Relation with Density Gradient Selected Sperm

Background

Sperm selection method is usually used to collect these cells for in vitro-assisted reproduction. Few studies reported the relationship of in vivo fertility and semen parameters after sperm selection; hence, the present study attempted to assess different semen parameters after post-thaw or sperm selection, using density gradient separation BoviPure®, to predict in vivo fertility.

Materials and Methods

In this experimental study, frozen semen quality of four Montbeliarde bulls were assessed after post-thaw (PT) or after sperm selection (SSp), using density gradient separation BoviPure®, to predict the fertility rate in vivo. In addition to PT or SSp, semen was examined for concentration, motility, morphology abnormalities, viability, acrosome and plasma membrane integrities. Fertility was measured as non-return rates within 56 days after the first insemination (NRR) or as corrected NRR, expressed as CNRR, to the factors influencing fertility using linear mixed model. Non-parametric Kruskal-Wallis test was performed to compare semen parameter variables. Fertility rates were compared using Chi-square test. Pearson correlation analysis was used to test the relationship between CNRR and semen parameters. Data was analysed using SPSS package program, version 21.0.

Results

Most of the examined bulls exhibited a high fertility rate (3/4 bulls, 62.1- 81.8% for NRR or 67.2-98.5% for CNRR). Fertility rate, expressed as CNRR, was significantly related to semen parameters after SSp, but not after PT. Thus, CNRR was increased with decrease of total motility, progressive spermatozoa and abaxial implantation frequencies after SSp (r=-0.999, P=0.001; r=-0.990, P=0.010; r=-0.988, P= 0.012, respectively); while, CNRR was decreased with decrease of SSp immotile spermatozoa (r=+0.995, P=0.005), underlying that maximal limit of determined immotile spermatozoa is 47%.

Conclusion

High frequencies of total and progressive motility spermatozoa, and abaxial implantation in gradient selected sperm appear to be not favorable for fertility in vivo.

Kinematic and spermatic recovery after selection by centrifugation in colloid solutions of ovine cryopreserved semen

ABSTRACT Frozen and thawed ovine semen undergo morphological and functional changes that prevent or decrease the efficiency of fertilization. Sperm selection methods seek to improve the quality and viability of the fertilizing materials. Four sperm selection methods were employed, using two silica colloidal solutions coated with silane (silica colloidal-silane) or by polyvinylpyrrolidone (silica colloidal-PVP), and varying the volume of colloidal solution. Sperm kinematic and sperm recovery were evaluated by means of CASA. The protocols using silica colloidal-silane showed higher total motility (TM), progressive motility (PM) and percentage of rapid sperm (%RAP) compared to the methods employing silica colloidal-PVP and to the samples prior to sperm selection. The silica colloidal-PVP had greater sperm recovery compared to the silica colloidal-silane. Only the method using 4mL of silica colloidal-PVP was not efficient in selecting samples with better quality compared to the samples analyzed prior to sperm selection. The methods using lower volumes of colloidal solution did not differ from those using higher volumes and the best results were shown by the method with 1mL silica colloidal-silane. The results found in the study indicated greater efficiency of the silica colloidal-silane solution for sperm selection of thawed ovine semen when compared to selection using silica colloidal-PVP. The method using 1mL of silica colloidal-silane was equally efficient to the method with higher volume, presenting itself as an alternative to process samples with lower sperm concentration.

Selection of red deer spermatozoa with different cryoresistance using density gradients

The objective of sperm selection media is selecting the best spermatozoa and to remove seminal plasma and diluent for using them in assisted reproductive techniques. It is known that individuals show different cryoresistance in response to the same freezing procedure. Our hypothesis was that the efficacy of selection media could be dissimilar for samples with different sperm quality after thawing. Epididymal sperm samples from mature Iberian red deer were collected and frozen. Males were classified as with high post-thaw sperm quality when sperm motility (SM) ≥ 70%, or as with low post-thaw sperm quality when SM ≤ 69%. Samples were centrifuged using the following density gradients (DG): Percoll^® , Puresperm^® and Bovipure^™ , and several functional sperm parameters were assessed after sperm selecting and washing. Males classified with high sperm quality had higher post-thawing values (p > .05) for all parameters evaluated, except for linearity index, than those categorized as low sperm quality. After selection, some sperm characteristics improved (viability, apoptosis and mitochondrial activity) for both groups, showing the males with high sperm quality higher values in all sperm parameters except for kinematic traits and DNA fragmentation index (%DFI), regardless of DG. Bovipure^™ yield lower values of sperm motility, viability, apoptosis and mitochondrial activity in relation to Percoll^® and Puresperm^® considering both quality groups. There was an interaction between the type of DG and sperm quality group for sperm viability (p = .040) and apoptosis (p = .003). Thus, Percoll^® selected less live and more apoptotic spermatozoa than Puresperm^® and Bovipure^™ for males with low sperm quality. In conclusion, the DG are more efficient selecting spermatozoa from samples with high sperm quality, acting differently depending on initial sperm quality.

In vitro and in vivo fertilization potential of cryopreserved spermatozoa from bull epididymides stored for up to 30 hours at ambient temperature (18 °C-20 °C)

The aims of this study were to compare the viability and in vivo and in vitro fertilization potential post-thaw sperm collected at different times postorchiectomy from bull epididymides (EP) at 18 °C to 20 °C, with those of semen collected by electroejaculation (EJ) from the same bulls. Semen samples were collected by EJ from 10 Zebu bulls and cryopreserved. A week later 20 epididymides from these bulls were obtained by orchiectomy and randomly divided into five groups (G) to be maintained at ambient temperature for 6, 12, 18, 24, and 30 hours before sperm recovery by retrograde flow. The sperm were cryopreserved, and post-thaw parameters were determined by both computer-assisted sperm analysis and morphologic analysis. In vitro fertilization of oocytes was performed to assess the cleavage rate, blastocyst rate, total number of cells, and hatching rate of embryos. The G30 sperm samples were also used for fixed time artificial insemination (FTAI) of Zebu heifers (n = 10). The results of post-thaw sperm viability showed that total and progressive motility and plasma membrane integrity were lower in sperm in which cryopreservation was delayed for 30 hours, showing a negative correlation of these parameters with delay before cryopreservation. In all groups, it was possible to obtain viable embryos, and embryos from G6 samples had more cells than the other groups. The greatest embryo production rates were observed in G6, G12 and G18 (27.2 to 32.2%) and it was significantly lower in G24 and G30 samples. For EJ, many individual variations were observed in embryo production potential between bulls. G30 samples, with only 5.2% of post-thaw progressive motility, were able to fertilize and produced a pregnancy. To the authors' knowledge, this is the first time in vitro embryos up to 8 days of development and a pregnancy after FTAI have been produced with sperm from bull epididymides that had been stored at 18 °C to 20 °C for up to 30 hours.

In vivo fertilizing ability of stallion spermatozoa processed by single layer centrifugation with Androcoll-E™

A colloid with a species specific silane-coated, silica-based formulation, optimized for stallion (Androcoll-E™), enables a better sub-population of spermatozoa to be selected from stallion ejaculates. However, such a practice has not been critically evaluated in stallions with fertility problems. In this study we evaluate whether single-layer centrifugation (SLC) through Androcoll-E™ could be used to enhance fertility rates in a subfertile stallion. Ejaculates were obtained from two different stallions, one Lusitano (fertile) and one Sorraia (subfertile), with distinct sperm characteristics and fertility. Motility, morphology, plasma membrane structural (eosin-nigrosin) and functional integrity (HOS test), mitochondrial functionality (Δψm; JC-1) and longevity (motility after 72 h cooling) after centrifugation in Androcoll-E™, as well as pregnancy rates obtained after artificial insemination (AI), with and without (control group) SLC-treated sperm were assessed. The effect of SLC on sperm characteristics, and fertility results were evaluated by ANOVA and Fisher procedures, respectively. Our results showed that SLC-selected sperm did not differ from the raw semen in terms of viability, morphology, response to hypo-osmotic conditions (HOS test) and mitochondrial membrane potential (↑ΔΨmit; JC-1). Sperm motility in cooled samples was not improved by SLC treatment. Our data show that SLC through Androcoll-E™ has no effect on pregnancy rates in the stallions used in this trial.

Effect of cryopreservation and single layer centrifugation on canine sperm DNA fragmentation assessed by the sperm chromatin dispersion test

The aims of this study were: 1) to assess the effect of freezing and thawing on dog sperm DNA fragmentation index (sDFI) using the sperm chromatin dispersion test (SCDt); and 2) to determine whether or not the sperm selection by single layer centrifugation (SLC) using Androcoll-C improves sperm DNA longevity in SLC-selected frozen-thawed dog semen samples. Semen samples were collected from 4 dogs using digital manipulation. After collection, ejaculates were pooled and cryopreserved following a standard protocol. Sperm motility and morphology were assessed before freezing and after thawing as a control for the cryopreservation method used. In experiment 1, sDFI was analyzed immediately before freezing and after thawing (baseline values), showing no significant differences between fresh and frozen-thawed semen samples. In experiment 2, frozen-thawed semen samples were processed or not by SLC using Androcoll-C and longevity of DNA were assessed in terms of sDFI after 24h of in vitro incubation at physiological temperature (38°C). The results showed low values of sDFI in SLC-selected semen in comparison to unselected samples. In conclusion, no effect of cryopreservation was observed on baseline values of dog sperm DNA fragmentation. Additionally, SLC-selection using Androcoll-C improved longevity of frozen-thawed sperm DNA assessed by the SCDt.

Effect of cysteamine supplementation during in vitro culture of early stage bovine embryos on blastocyst rate and quality

The aim of this study was to evaluate whether the addition of cysteamine to the in vitro culture media enhances the yield, hatching rate, total cell number and inner cell mass/total cell number ratio of bovine embryos. A total of 933 bovine oocytes collected from ovaries of 60 slaughtered donors were subjected to in vitro maturation and in vitro fertilization. Following fertilization, embryos were cultured in synthetic oviductal fluid without glucose. After 24 h embryos were transferred into synthetic oviductal fluid with 1.5 mM glucose and 0 (control), 50, 100 and 200 µM of cysteamine. After 48 h, the embryos were transferred into synthetic oviductal fluid with glucose but without cysteamine and cultured until Day 9. The number of cleaved embryos on Day 2, the total number of blastocysts on Day 7 and the number of hatched blastocysts on Day 9 were calculated. Differential staining of inner cell mass and trophectoderm cells of blastocysts were performed on Day 7 and Day 9 of in vitro culture. Supplementation of in vitro culture media with 100 µM cysteamine increased the blastocyst yield (P < 0.05) without affecting the hatching rate. Furthermore, the embryos cultured in the presence of 100 µM cysteamine had significantly higher number of inner cell mass cells (P < 0.05) and the proportion of inner cell mass cells (P < 0.05) compared with the controls. The results of the present study demonstrated that the addition of 100 µM cysteamine to the in vitro culture media improved blastocyst production rate and enhance embryo quality, which could lead to the improvement of the in vitro culture system for bovine embryos.

Evaluation of the qualitative and quantitative effectiveness of three media of centrifugation (Maxifreeze, Cushion Fluid Equine, and PureSperm 100) in preparation of fresh or frozen-thawed brown bear spermatozoa

Centrifugation is a crucial procedure in sperm cryopreservation protocols of brown bear (Ursus arctos), because the semen must be processed to increase sperm concentration and/or clean urine-contaminated samples. The efficacy of three media for centrifugation (Maxifreeze [IMV technologies, L'Aigle, France], Cushion Fluid Equine (Minitübe, Tiefenbach, Germany), and PureSperm [Nidacon, Gothenburg, Sweden]) on the quality of bear spermatozoa was evaluated. In experiment one, two cushioned media used for protecting against mechanical stress during centrifugation were analyzed. In experiment two, a density gradient based on PureSperm was assessed in relation to the maximum retrieval and the quality of fresh spermatozoa, and the freezability of the spermatozoa selected in this density gradient was studied in experiment three. Finally, the selection of frozen-thawed sperm using PureSperm was analyzed in experiment four. Our results indicate that the use of dense isotonic cushion solutions (Maxifreeze, Cushion Fluid Equine) in centrifugation did not improve the quality of recovered spermatozoa compared with standard centrifugation. However, a density gradient prepared with PureSperm improved the quality of spermatozoa in fresh semen and frozen-thawed semen, but the spermatozoa selected from the fresh sample with this density gradient did not show a better resistance to freezing with this density gradient in comparison with the control sample.

Effect of Osmolarity and Density of Colloid Formulations on the Outcome of SLC-Selection of Stallion Spermatozoa

The osmolarity and density of colloids used to prepare spermatozoa for assisted reproduction may affect sperm quality in the resultant preparation. In this study, two osmolarities of Androcoll-E for single-layer or density gradient centrifugation of stallion spermatozoa were compared: “normal” (320 mOsm) or “high” (345 mOsm). Mean yields for the two centrifugation techniques did not differ between treatments or osmolarities (single layer centrifugation: 30.19 ± 16.9 × 10⁶ and 25.8 ± 18.5 × 10⁶ spermatozoa; density gradient centrifugation: 31.84 ± 19.7 × 10⁶ and 26.46 ± 20.0 × 10⁶ spermatozoa respectively for the two osmolarities). However, use of the high osmolarity colloid for single layer centrifugation increased the proportion of morphologically normal spermatozoa (P < .05). Therefore, increasing the osmolarity of the colloid formulation may be beneficial for processing ejaculates containing a high proportion of abnormal spermatozoa by SLC. Reducing the density of the colloid used for the SLC substantially increased the yield of motile spermatozoa compared to the normal density colloid (mean ± SD: 72.6 ± 28.9 × 10⁶ versus 28.9 ± 24.7 × 10⁶), while also prolonging sperm survival by 24 hours compared to the uncentrifuged ejaculate. This increased yield may render Single Layer Centrifugation practical for use in the field.

Analysis of selected sperm by density gradient centrifugation might aid in the estimation of in vivo fertility of thawed ram spermatozoa

The aim of the present study was to evaluate the effect of selecting a sperm subpopulation by means of a discontinuous density gradient centrifugation (DGC) on the quality of ram thawed semen, and the relationships between sperm parameters assessed in unselected and in selected sperm samples with in vivo fertility after intrauterine artificial insemination (IUI) using unselected sperm samples. Semen samples from twenty males were collected by artificial vagina and cryopreserved following a standard protocol. After thawing, unselected sperm samples were used in an in vivo fertility trial and sperm motility (subjective and objective, assessed by means of CASA) and membrane and acrosomal integrities (microscopy) were evaluated on unselected and selected sperm samples. In addition, plasmalemma integrity (YO-PRO-1/PI), membrane fluidity (Merocyanine 540/YO-PRO-1), mitochondrial activity (Mitotracker Deep Red/YO-PRO-1), and DNA fragmentation index (%DFI) assessed by Sperm Chromatin Structure Assay (SCSA) were evaluated by flow cytometry before and after sperm processing using DGC. Results showed that DGC improved all sperm parameters significantly, except the %DFI, which increased after the selection procedure. No relationships were found between sperm parameters evaluated in unselected sperm samples and in vivo fertility. However, we found a positive correlation between spermatozoa with high membrane fluidity within the viable sperm population (VIABMerocyanine+) evaluated in selected sperm samples and in vivo fertility (r = 0.370, P = 0.019). In conclusion, our results suggest that selected spermatozoa represent a sperm subpopulation different to the unselected one that could be related with the in vivo fertility.

Selection of boar spermatozoa using centrifugation on a glycidoxypropyltrimethoxysilane-coated silica colloid

Use of sperm separation methods such as density gradient centrifugation for selecting the best spermatozoa for animal breeding is constrained by the problem of dealing with the large volumes of ejaculate produced by the males of some species, such as boars. The purpose of this study was to compare density gradient centrifugation (DGC) with centrifugation on a single layer of colloid (SLC) for the preparation of ejaculated boar spermatozoa using Androcoll(TM)-P. There was no difference between the two techniques in terms of sperm motility or duration of motility after selection, and sperm motility was retained for at least 24 h longer in the centrifuged sperm preparations than in controls (uncentrifuged aliquots). Sperm motility was significantly better (P<0.001) in the centrifuged sperm preparations (means +/- sd: SLC 79.6 +/- 8.1% and DGC 74.2 +/- 12.0%) than in the uncentrifuged controls (62.9 +/- 12.7%). The mean yield of motile spermatozoa for SLC was 67.5 +/- 25.6%, and for DGC it was 59.6% +/- 22.3% (not significant, ns). Sperm survival was significantly increased by colloid centrifugation (control 3.1 +/- 0.3 days, SLC 5.5 +/- 0.79 days, DGC 5.75 +/- 0.62 days; P<0.001 for uncentrifuged versus centrifuged; SLC vs. DGC, ns). Moreover, boar spermatozoa could be stored for 24 h before centrifugation without any detrimental effect on sperm motility or duration of motility. In a further experiment, larger volumes of ejaculate were processed easily on a modified SLC, indicating that this method may be practical for processing large volumes of boar ejaculates.

State of the art in farm animal sperm evaluation

Our ability to screen the structural and functional integrity of the spermatozoon in vitro has increased markedly over the past decades, but our capacity to estimate the fertility of a semen sample or of the sire from which it has been collected, especially in selected farm animal breeders, has not. The estimation of fertility is constrained by several factors (e.g. type of cell, analysis strength, sperm deposition strategies, recordings of fertility), including the fact that the ejaculate is composed of a diverse sperm population. Such cell heterogeneity is reflected not only in differences in the intactness of attributes needed for fertilisation, such as motility or morphology, but also in the relative ability of the spermatozoa to remain fertile over time, to sustain selection steps and responses to exogenous stimuli similar to those during sperm transport in the female genital tract, all of which account for innate variations in the fertilising ability among doses, ejaculates and sires. Determination of how large such a sperm population with competence for fertilisation and in-built ability to display these attributes under physiological signalling is would allow for a better estimation o f fertility, provided that th e particular s ire produces this sub-population in a repeatable manner. The value of these analyses is discussed in the present paper.