Single layer centrifugation (SLC) improves sperm quality of cryopreserved Blanca-Celtibérica buck semen

Single layer centrifugation as a method for bacterial reduction in bull semen for assisted reproduction

Semen samples contain bacteria originating from the animal urogenital tract, environment, and/or contamination during semen processing, negatively affecting sperm quality by producing toxins and/or competing for nutrients in extenders. The aims of this study were to evaluate two methods of Single-layer centrifuges (SLC), high and low density colloid, as a method for bacterial removal from bull semen, and to evaluate sperm quality after treatment. In total, semen samples from 20 bulls (3 ejaculates per bull) were used in this study. Bacterial reduction was evaluated by bacterial quantification (colony forming unit - CFU/mL) while bacterial identification was performed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) after culturing bacteria on blood agar. Sperm motility parameters were evaluated by Computer Assisted Sperm Analyses (CASA), and sperm chromatin structure assay (SCSA) by Flow cytometry. Both, High and Low density SLC reduced number of bacteria significantly (p < 0.001) compared with control. The difference in bacterial count between High and Low SLC was also significant (p < 0.001). Furthermore, High density SLC was successful in removing almost all Bacillus and Proteus spp. Most CASA parameters were significantly improved after both treatments (p < 0.001, p < 0.01, p < 0.05). The Deoxyribonucleic acid (DNA) fragmentation index evaluated by SCSA in High (p < 0.01) and Low (p < 0.05) SLC group differed significantly compared with control. Single-layer centrifugation (SLC) with either a high or a low density colloid is a suitable method for bacterial removal in bull semen.

Practical Method for Freezing Buck Semen

Simple Summary

Goat semen was previously considered to be problematic to freeze because of reactions between the semen and the components of the freezing media that were available at the time. However, there have been reports of several successful attempts to freeze goat semen in recent decades using various protocols, resulting in usable post-thaw sperm samples. In the present study, we adapted some of these methods to suit the particular conditions under which we had to work. We were able to produce thawed samples with acceptable sperm quality which were sent to a sperm bank for long-term storage.

Abstract

Although several protocols for cryopreserving buck semen are described in the literature, they differ widely in factors such as season and method of semen collection, extender and sperm concentration. Therefore, choosing a protocol that is suitable for a particular on-farm situation can be problematic. In the present study, semen was collected by artificial vagina from seven bucks on a farm located approximately 90 minutes’ drive away from the laboratory, about 6 weeks before the start of the goat breeding season. The semen was immediately extended in warm semen extender containing soy lecithin and was placed in an insulated box with a cold pack for up to 4 h, during semen collection from the remaining bucks and subsequent transport to the laboratory. Following centrifugation at 4 °C and resuspension in the soy lecithin extender to a sperm concentration of 800 × 10⁶ spermatozoa/mL, 0.25 mL plastic straws were filled and frozen in racks 4 cm above the surface of liquid nitrogen. This simple protocol resulted in an acceptable post-thaw quality for all seven bucks, with a mean post-thaw motility of 55 ± 21% and mean fragmented chromatin of 3.27 ± 1.39%. Normal sperm morphology was >90% in all ejaculates. The semen was sent to a gamete bank for long-term storage.

Impact of Oxidative Stress on Male Reproduction in Domestic and Wild Animals

Oxidative stress occurs when the levels of reactive oxygen species (ROS) overcome the antioxidant defenses of the organism, jeopardizing several biological functions, including reproduction. In the male reproductive system, oxidative stress not only impairs sperm fertility but also compromises offspring health and survival, inducing oxidative damage to lipids, proteins and nucleic acids. Although a clear link between oxidative stress and male fertility disorders has been demonstrated in humans and laboratory rodents, little information is available about the implications of impaired redox homeostasis in the male fertility of domestic and wild animals. Therefore, this review aims to provide an update regarding the intrinsic and extrinsic factors that are associated with oxidative stress in the male reproductive system and their impact on the reproductive performance of domestic and wild animals. The most recent strategies for palliating the detrimental effects of oxidative stress on male fertility are reviewed together with their potential economic and ecological implications in the livestock industry and biodiversity conservation.

Does single-layer centrifugation with Bovicoll improve sperm quality of frozen-thawed semen in Fleckvieh bulls?

The aim of the present study was to evaluate the effect of sperm selection by single-layer centrifugation (SLC) performed before freezing on sperm quality after thawing of Fleckvieh bull semen. Ejaculates from 22 bulls were collected by artificial vagina and divided into two aliquots. One aliquot (control sample) was diluted with Steridyl^® and frozen over nitrogen vapour in a Digitcool freezer (IMV Technologies). Sperm from the second aliquot (SLC sample) was selected using the SLC technique with Bovicoll colloid and then frozen over nitrogen vapour in a Digitcool freezer. After thawing, both samples (control and SLC) were evaluated by computer-aided sperm analysis (CASA; SCA 6.4 System; Microptic S.L) for sperm motility parameters. Integrity of the plasma membrane (viability), high mitochondrial membrane potential (HMMP) and acrosome integrity were assessed using a Guava® easyCyte flow cytometer (IMV Technologies). Morphological examination of spermatozoa was performed by Differential Interference Contrast microscopy (Leica DMi8). Morphological examination of live, immobilized spermatozoa was analysed under high magnification (≥6,600×). After thawing, the mean sperm viability of the control sample was 51.57%, compared to 40.37% for the SLC sample (p < .01). HMMP was higher (p < .01) in the control sample (40.37% versus 28.96%), and the mean of live spermatozoa with damaged acrosome was significantly higher (p < .03) in the SLC sample (1.63% versus 1.95%). The mean percentage of motile spermatozoa was 80.17% in the control sample, compared to 75.14% in the SLC sample (p < .0195), and rapid subpopulation reduced from 20.08% to 8.99% (p < .0001) after SLC. Percentage of hyperactivated sperm decreased from 12.23% to 4.28% (p < .0001) after SLC. Given the overall results, the sperm quality of thawed Fleckvieh bull semen was not improved when sperm were selected by SLC before freezing.

Effect of colloid centrifugation on boar sperm quality during storage and function in in vitro fertilization

Ejaculates contain a heterogeneous population of spermatozoa with differing ability to fertilize. It may be possible to reduce the numbers of spermatozoa required for artificial insemination or in vitro fertilization by selecting the sperm sub-population that possesses certain desired characteristics. This review describes what is meant by sperm quality, mentions different methods of sperm selection and then describes the effect of sperm selection by colloid centrifugation on boar sperm quality, both quality during storage and functionality in in vitro fertilization. Several versions of the technique known as Single Layer Centrifugation are available depending on the volume of ejaculate to be processed. Semen can be processed in volumes ranging from 0.25 to 150 mL, in suitably sized tubes. Processing small volumes of semen (0.25 mL on 1 mL colloid) is best done in a 15 mL tube, since the area of the interface between the semen and colloid is greater than in a 1.5 mL microcentrifuge tube. Potential uses of this processing technique are described, such as conservation breeding of rare breeds and removal of pathogens. Reducing the bacterial load in semen by single layer centrifugation though a low density colloid could provide an alternative to the use of antibiotics in semen extenders, and is an interesting development.

Single layer colloid centrifugation technique improves motility, viability and chromatin integrity of ram spermatozoa after thawing

The cell membrane of ram spermatozoa is more sensitive to the freezing process than in other species due to its composition. As a result, the quality and viability of frozen thawed ram spermatozoa are often poor, which together with the specific structure of the ewe's cervix are the main reasons for lower fertility in ewes after intracervical insemination. In the present study we investigated the effects of semen centrifugation through a single layer of a species-specific colloid (Androcoll-O) on post-thaw quality of ram spermatozoa. Motility, viability and morphology were analysed 0, 6, 12 and 24 h after thawing. DNA fragmentation index (%DFI) of the samples was assessed 0 h after thawing, by SCSA™. Membrane and acrosome integrity of spermatozoa were analysed by Sybr-14/PI/PNA test 0 h after thawing. The proportion of motile spermatozoa was significantly higher in SLC - selected samples in comparison to control (not SLC - selected) samples at 0, 6, 12 (P < 0.001) and 24 h (P < 0.05). The proportion of viable spermatozoa was also significantly higher in SLC - selected samples in comparison to control samples at all times (P < 0.001). The proportion of abnormal acrosomes and morphologically abnormal spermatozoa (MAS) were significantly lower in SLC - selected samples compared to control samples at all times (P < 0.001). Analysis of chromatin stability revealed significantly lower %DFI values in SLC - selected samples compared to control samples (P < 0.001). The SYBR-14/PI/PNA test also revealed significantly better values in SLC - selected compared to control samples (P < 0.05). In conclusion, single layer colloid centrifugation significantly improved post-thaw quality and longevity of ram spermatozoa, making it suitable for artificial insemination initiatives.

Colloid centrifugation of fresh semen improves post-thaw quality of cryopreserved dromedary camel spermatozoa

Colloids have been successfully used in a number of species to improve sperm populations for IVF and for cryopreservation The usefulness of Single Layer Centrifugation (SLC) for freezing dromedary camel spermatozoa in two different extenders was evaluated by examining the motility, viability, acrosome status, DNA integrity, and ability of cryopreserved sperm to penetrate oocytes in vitro in a heterologus IVF system. Two ejaculates from each of five males were divided into four aliquots: two were processed by SLC (selected) while two were centrifuged without colloid (control). Pellets were cryopreserved in Green Buffer or INRA-96® containing 3% glycerol and evaluated at 0 and 1 h post thawed. The SLC improved post-thaw total and progressive motility at 0 (both P < 0.0001) and 1 (P < 0.001; P < 0.01, respectively) h, and STR (both P < 0.05) and BCF (both P < 0.001) at 0 h. Sperm viability and acrosome integrity (both P < 0.001) were improved at both time points. Sperm frozen in Green Buffer had greater total and progressive motilities at 0 (both P < 0.001) and 1 (both P < 0.001) h than INRA-96® samples. Spermatozoa in Green Buffer also had a greater VAP, VCL and VSL at 0 h and improved viability and acrosome integrity at 0 h (P < 0.05; P = 0.001, respectively) and 1 h (P < 0.05; P < 0.001, respectively). Viability of SLC spermatozoa was improved in Green Buffer at 1 h (P < 0.05). Oocyte penetration (P < 0.05) and pronuclear formation (P < 0.01) were greater with SLC-selected spermatozoa than non-selected spermatozoa, regardless of extender. No difference was observed between treatments or extenders in the mean number of spermatozoa per oocyte penetrated. The SLC spermatozoa had less (P < 0.01) DNA fragmentation compared to controls. The DNA fragmentation was moderately and negatively correlated with penetration (r = -0.4162; P = 0.02) and pronuclear formation (r = -0.3390; P < 0.01). In conclusion, colloid centrifugation of spermatozoa and cryopreservation in Green Buffer improves post thaw motility variables and IVF performance of dromedary camel spermatozoa.

Effect of Single Layer Centrifugation Porcicoll (70%, 80% and 90%) or supplementation with reduced glutathione, seminal plasma and bovine serum albumin on frozen-thawed boar sperm

Selecting the optimal sperm population is essential for success with reproductive techniques. Porcicoll (formerly Androcoll-P) is a colloid formulation for selection of high-quality boar spermatozoa by single layer centrifugation (SLC). To date, most studies have been carried out with fresh semen and large volumes. We carried out 2 experiments to test the use of Porcicoll for thawed boar semen in small volumes. In Experiment 1, cryopreserved semen doses were thawed, split in 200-μL aliquots and layered on 1mL of Porcicoll 70%, 80% or 90%, or buffer without colloid. We assessed sperm recovery (the proportion of the loading dose that appeared in the pellet, %), and the physiology of the selected spermatozoa (flow cytometry: Viability, apoptotic changes, capacitation, mitochondrial activity, intracellular reactive oxygen species). The most suitable proportion was Porcicoll 80%, allowing acceptable sperm recovery (16.9±4.2%, compared to 70% (35.4%±3.0, p<0.001) and 90% (8.2%±3.0, P=0.001), and improved quality (mitochondrial activity: Porcicoll 80%: 77.7±1% vs Control: 60.3±0.7%, P<0.05). In Experiment 2, we compared 3 supplements to Porcicoll 80%: 500mM reduced glutathione (GSH), 20% seminal plasma (SP) and 0.5% bovine serum albumin (BSA). Supplementation with GSH or BSA did not cause relevant changes relative to Control. In contrast, SP induced membrane and acrosomal changes resembling capacitation, which might preclude its use in some applications, and decreased recovery (5.5%±1.9 vs. 24.3%±1.2 Control; P<0.001). However, it could be useful prior to other applications such as in vitro fertilisation. Overall, Porcicoll is an effective colloid for isolating a high-quality population from thawed boar sperm, 80% being a balanced option for good recovery and high quality. Supplements could be useful depending on the proposed use of the spermatozoa.

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.

Improving sperm banking efficiency in endangered species through the use of a sperm selection method in brown bear (Ursus arctos) thawed sperm

Background

Sperm selection methods such as Single Layer Centrifugation (SLC) have been demonstrated to be a useful tool to improve the quality of sperm samples and therefore to increase the efficiency of other artificial reproductive techniques in several species. This procedure could help to improve the quality of genetic resource banks, which is essential for endangered species. In contrast, these sperm selection methods are optimized and focused on farm animals, where the recovery task is not as important as in endangered species because of their higher sperm availability. The aim of this study was to evaluate two centrifugation methods (300 x g/20 min and 600 x g/10 min) and three concentrations of SLC media (Androcoll-Bear −80, 65 and 50%) to optimise the procedure in order to recover as many sperm with the highest quality as possible. Sperm morphology could be important in the hydrodynamic relationship between the cell and centrifugation medium and thus the effect of sperm head morphometry on sperm yield and its hydrodynamic relationship were studied.

Results

The samples selected with Androcoll-Bear 65% showed a very good yield (53.1 ± 2.9) although the yield from Androcoll-Bear 80% was lower (19.3 ± 3.3). The latter showed higher values of motility than the control immediately after post-thawing selection. However, both concentrations of colloid (65 and 80%) showed higher values of viable sperm and viable sperm with intact acrosome than the control. After an incubation of 2 h at 37 °C, the samples from Androcoll-Bear 80% had higher kinematics and proportion of viable sperm with intact acrosome. In the morphometric analysis, the sperm selected by the Androcoll-Bear 80% showed a head with a bigger area which was more elongated than the sperm from other treatments.

Conclusions

We conclude that sperm selection with Androcoll-Bear at either 65% or 80% is a suitable technique that allows a sperm population with better quality than the initial sample to be obtained. We recommend the use of Androcoll-Bear 65% since the yield is better than Androcoll-Bear 80%. Our findings pave the way for further research on application of sperm selection techniques to sperm banking in the brown bear.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1124-2) contains supplementary material, which is available to authorized users.

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.

Effect of sperm preparation on development of bovine blastocyst in vitro

Sperm preparation is an important step in the in vitro production of embryos. Centrifugation through colloids has been used to select normal sperm for assisted reproduction in several species. Animal models can sometimes be used as a preliminary step to investigate sperm preparation methods that are potentially of use for human fertility treatments. In this study bovine semen was prepared using three variants of the single-layer centrifugation sperm selection technique (Small, Mini, Mini-EP) with Bovicoll (Androcoll-B). Computer-assisted sperm motility analysis, the hypo-osmotic swelling test, and the sperm chromatin structure assay were performed on unselected (control) and SLC-selected sperm samples. Mini and Mini-EP gave the highest yield of motile spermatozoa, progressive motility and membrane integrity. In vitro fertilization trials were performed to investigate the fertilizing ability of the frozen–thawed bovine spermatozoa selected with Bovicoll. Mini-SLC (single-layer centrifugation) and swim-up (Control) were performed and cleavage rate and blastocyst rate did not differ significantly between groups. As there was a trend to an increased number of cells in blastocysts in the SLC group, the Mini-SLC method is at least as good as swim-up for selecting frozen–thawed bull spermatozoa for in vitro fertilization (IVF). This method could potentially be used to prepare human sperm for assisted reproduction.

Colloid single-layer centrifugation improves post-thaw donkey (Equus asinus) sperm quality and is related to ejaculate freezability

The aim of this study was to determine whether colloid single-layer centrifugation (SLC) improves post-thaw donkey sperm quality and if this potential enhancement is related to ejaculate freezability. Semen from Andalusian donkeys was frozen following a standard protocol. SLC was performed on frozen-thawed semen and post-thaw sperm parameters were compared with uncentrifuged samples. Sperm quality was estimated by integrating in a single value sperm motility (assessed by computer-assisted sperm analysis), morphology and viability (evaluated under brightfield or fluorescence microscopy). Sperm freezability was calculated as the relationship between sperm quality obtained before freezing and after thawing. Ejaculates were classified into low, medium and high freezability groups using the 25th and 75th percentiles as thresholds. All sperm parameters were significantly (P<0.01) higher in SLC-selected samples in comparison to uncentrifuged frozen-thawed semen and several kinematic parameters were even higher than those obtained in fresh semen. The increment of sperm parameters after SLC selection was correlated with ejaculate freezability, obtaining the highest values after SLC in semen samples with low freezability. We concluded that, based on the sperm-quality parameters evaluated, SLC can be a suitable procedure to improve post-thaw sperm quality of cryopreserved donkey semen, in particular for those ejaculates with low freezability.

Use of Androcoll-S after thawing improves the quality of electroejaculated and epididymal sperm samples from red deer

Single Layer Centrifugation is a useful technique to select sperm with good quality. The use of selection methods such as Androcoll could become an important tool to improve the quality of sperm samples and therefore to improve other artificial reproductive techniques such as sperm sex sorting, in vitro fertilization or AI. The aim of this study was to evaluate the effect of a Single Layer Centrifugation with Androcoll-S on the sperm quality of red deer sperm samples of two different origins, electroejaculated samples and epididymal samples obtained post-mortem, after thawing and after an incubation for 2h at 37°C. Sperm motility, viability, membrane permeability, mitochondrial activity, acrosomal status and DNA fragmentation were determined for all samples. The samples selected by Androcoll-S showed an improvement in sperm kinematics compared to unselected samples after thawing and after incubation. The same effect was observed in parameters such as viability, mitochondrial activity or acrosomal status which were improved after the selection. In contrast, no difference was found in DNA fragmentation between selected and unselected samples within the same sperm type. We conclude that sperm selection by SLC with Androcoll-S after thawing for red deer sperm of both types is a suitable technique that allows sperm quality in both types of sperm samples to be improved, thereby improving other assisted reproductive techniques. Further studies (IVF and in vivo fertilization) are required to determine whether this improvement can increase fertility, as has been shown for other species.

Differences in preservation of canine chilled semen using simple sperm washing, single-layer centrifugation and modified swim-up preparation techniques

This study compared the efficacy of simple sperm washing (SW), single-layer centrifugation (SLC) and modified swim-up (SU) techniques in the preparation of dog spermatozoa for cooling. Eighteen ejaculates, collected from three dogs (six per dog), were pooled (three ejaculates per pool) and divided into three aliquots: (1) one aliquot was washed and cooled at 5°C for 72h, considered as control (SW-control), (2) the second aliquot was selected by SLC through Androcoll-C and subsequently cooled in the same way as the SW-control samples (SLC-AC) and (3) the last aliquot was selected by a modified SU method with Androcoll-C and cooled as mentioned above (SU-AC). Assessment of sperm motility, sperm morphology, sperm membrane integrity and acrosome integrity were performed on aliquots of fresh semen and chilled-rewarmed samples. Sperm membrane integrity and progressive motility were significantly (PPP>0.05). The recovery rates were not significantly (P>0.05) different between SW-control, SLC-AC and SU-AC samples. Our results confirm that SU-AC may be a successful method for the preparation of dog spermatozoa for cooling.