Suitability and effectiveness of single layer centrifugation using Androcoll-P in the cryopreservation protocol for boar spermatozoa

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.

Low-density colloid centrifugation removes bacteria from boar semen doses after spiking with selected species

Single-layer centrifugation (SLC) with a low-density colloid is an efficient method for removing contaminating microorganisms from boar semen while recovering most spermatozoa from the original sample. This study tested the performance of this technique, using 50-ml tubes, by spiking commercial semen doses prepared without antibiotics with selected bacterial species followed by storage at 17 °C. The doses were spiked up to 10²/ml CFU (colony forming units) of the bacteria Burkholderia ambifaria, Pseudomonas aeruginosa, and Staphylococcus simulans. The semen was processed by SLC (15 ml of sample and 15 ml of colloid) with the colloid Porcicoll at 20% (P20) and 30% (P30), with a spiked control (CTL) and an unspiked control (CTL0), analyzing microbiology and sperm quality on days 0, 3 and 7. SLC completely removed B. ambifaria and S. simulans, considerably reducing P. aeruginosa and overall contamination (especially P30, ∼10⁴ CFU/ml of total contamination on day 7, median). Sperm viability was lower in P20 and P30 samples at day 0, with higher cytoplasmic ROS. Still, results were similar in all groups on day 3 and reversed on day 7, indicating a protective effect of SLC (possibly directly by removal of damaged sperm and indirectly because of lower bacterial contamination). Sperm chromatin was affected by the treatment (lower DNA fragmentation and chromatin decondensation) and storage (higher overall condensation on day 7 as per chromomycin A3 and monobromobimane staining). In conclusion, SLC with low-density colloids can remove most bacteria in a controlled contamination design while potentially improving sperm quality and long-term storage at practical temperatures.

Influence of Single Layer Centrifugation with Canicoll on Semen Freezability in Dogs

Simple Summary

Freezing dog semen is not always possible due to low quality sperm or poor survival during freezing. In order to make this assisted reproductive technique available to a larger number of dogs, this study investigated the benefit of selecting the best spermatozoa before freezing using single layer centrifugation (SLC). The results indicated that this technique was effective in separating spermatozoa according to their quality, although this resulted in losing some good quality spermatozoa. After thawing, spermatozoa centrifuged by SLC were of better quality than after standard centrifugation. However, spermatozoa from suboptimal quality semen did not survive freezing as well as spermatozoa from semen of optimal quality, even after SLC. Single layer centrifugation, therefore, makes it possible to obtain better quality spermatozoa after thawing but is not sufficient on its own to improve the inferior freezing ability of spermatozoa from suboptimal quality semen. So far, eighteen pups were born after insemination with SLC-selected frozen-thawed semen, proving that these selected spermatozoa remain fertile.

Abstract

This study evaluated how semen selection by single layer centrifugation (SLC) with Canicoll affects semen freezability in dogs. A total of eighteen ejaculates, collected from dogs with optimal and suboptimal semen quality (optimal: normal morphology (NM) ≥ 80%, n = 9; suboptimal: NM between 60 and 79%, n = 9), were divided into two aliquots and subjected to standard centrifugation or SLC before cryopreservation. Motility, NM, membrane integrity, mitochondrial membrane potential (MMP), and DNA integrity were improved in fresh samples after SLC, regardless of semen quality, but at the expense of some good quality spermatozoa. After thawing, NM and membrane integrity were improved in SLC-selected semen in both semen qualities. Interestingly, MMP was also higher but only in optimal quality semen. Still, spermatozoa from suboptimal quality semen did not survive freezing to the same extent as spermatozoa from optimal quality semen, even after selecting superior spermatozoa. Semen selection with Canicoll is, therefore, an effective technique to isolate a subpopulation of high-quality spermatozoa and obtain sperm samples of better quality after thawing, but is not sufficient to improve the intrinsic inferior freezability of suboptimal quality semen. So far, eighteen pups were born after insemination with SLC-selected frozen-thawed semen, proving that these selected spermatozoa remain fertile.

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.

Low density Porcicoll separates spermatozoa from bacteria and retains sperm quality

Antibiotics are added to semen extenders to control the growth of bacteria contaminating semen during collection but may contribute to the development of antibiotic resistance. An alternative would be physical separation of spermatozoa from bacteria. The objective of the present study was to evaluate two low densities of Porcicoll for removal of bacteria, and for their effect on sperm recovery and sperm quality. Semen was collected from boars at a commercial station. Aliquots of 8 extended ejaculates were subjected to colloid centrifugation through 20% Porcicoll (P20) and 30% Porcicoll (P30) in 500 mL tubes and then stored at 17 °C. Microbiological examination and sperm quality evaluation (computer assisted sperm analysis and flow cytometry) were carried out on controls and all colloid-selected samples immediately after preparation and again after storage for 3 and 7 days. The microorganisms found were mainly bacteria from the environment, gut or skin. There was a considerable reduction or complete removal of some bacteria by both colloids. Recovery rates were 86% for P20 and 81% for P30. Sperm quality was not adversely affected by colloid centrifugation on day 0, and thereafter showed a more gradual deterioration in colloid centrifuged samples than in controls, possibly due to lower bacterial contamination. There were no differences in sperm quality between the two colloid treatments. Thus, these results show that contaminating bacteria in semen can be controlled by centrifugation through low density colloids.

Use of Androcoll-ETM to Separate Frozen-Thawed Llama Sperm From Seminal Plasma and Diluent

It is not easy to separate frozen-thawed South American camelid sperm from seminal plasma (SP) and diluents to be used for in vitro embryo production. The objective of this study was to evaluate Androcoll-E™ (AE) efficiency to separate llama sperm from SP and freezing extender in frozen-thawed semen. A total of 22 ejaculates from five Lama glama males were collected using electroejaculation. After performing semen analysis (sperm motility, concentration, viability, membrane function, and acrosome integrity), samples were cryopreserved with a diluent containing lactose, ethylenediaminetetraacetic acid (EDTA), egg yolk, and 7% dimethylformamide. After thawing, samples were divided in aliquots, one of which was used as a control and the others processed by AE. Experiment 1 (12 ejaculates): 100 μl of frozen-thawed semen was placed on top of 1,000 μl AE column and centrifuged at 800 g for 10 min. Experiment 2 (10 ejaculates): two samples of 100 μl of frozen-thawed semen were placed on two columns of 500 μl AE each, and both were centrifuged at 800 g for 10 and 20 min, respectively. Pellets were resuspended in Tyrode's albumin lactate pyruvate (TALP) medium, and sperm parameters were evaluated. A significant decrease in all sperm parameters was observed in thawed samples compared to raw semen. AE allowed the separation of frozen-thawed sperm from SP and freezing extender independently from the height of the column used and time of centrifugation assayed. Although no significant differences were found between AE columns, higher sperm recovery was observed with 500 μl of AE coupled with 20 min of centrifugation. Despite the significant decrease observed in sperm motility in AE samples, no changes in sperm viability, membrane function, and acrosome integrity were observed when comparing control thawed semen with the sperm recovered after AE (p > 0.05). The use of AE columns, either 500 or 1,000 μl, allows the separation of frozen-thawed llama sperm from SP and freezing extender, preserving the viability, membrane function, and acrosome integrity. Of the protocols studied, 800 g centrifugation during 20 min using a 500 μl column of AE would be the method of choice to process frozen-thawed llama semen destined for reproductive biotechnologies.

Single Layer Centrifugation Improves the Quality of Fresh Donkey Semen and Modifies the Sperm Ability to Interact with Polymorphonuclear Neutrophils

Simple Summary

Donkey Artificial Insemination (AI) with frozen/thawed semen results in poor fertility outcomes. Jennies show a significant post-AI endometrial reaction, with a large amount of defense cells—polymorphonuclear neutrophils (PMN)—migrating to the uterine lumen. Seminal plasma (SP) has a detrimental effect on sperm conservation and its removal is a necessary step in the semen freezing protocol. However, several SP proteins seem to control sperm-PMN binding. Single layer centrifugation (SLC) with colloids, which has been used to select spermatozoa and improve reproductive performance in different species, is known to remove SP proteins attached to the sperm membrane. In this study, two experiments were performed. The first one compared the quality of SLC-selected and non-selected fresh donkey spermatozoa. In the second experiment, PMN obtained from the peripheral blood were co-incubated with selected and unselected spermatozoa, and the interaction between PMN and spermatozoa was analyzed. In conclusion, SLC of fresh donkey semen increases the proportion of functionally intact spermatozoa and appears to remove the SP proteins that inhibit sperm-PMN binding, thus increasing sperm phagocytosis by PMN.

Abstract

This study sought to determine whether single layer centrifugation (SLC) of fresh donkey semen with Equicoll has any impact on sperm quality parameters and on the modulation of endometrial reaction following semen deposition using an in vitro model. Seventeen ejaculates from five jackasses were obtained using an artificial vagina and diluted in a skim-milk extender. Samples were either selected through SLC (Equicoll) or non-treated (control). Two experiments were performed. The first one consisted of incubating selected or non-selected spermatozoa at 38 °C for 180 min. Integrity and lipid disorder of sperm plasma membrane, mitochondrial membrane potential, and intracellular levels of calcium and reactive oxygen species were evaluated at 0, 60, 120, and 180 min. In the second experiment, polymorphonuclear neutrophils (PMN) isolated from jennies blood were mixed with selected and unselected spermatozoa. Interaction between spermatozoa and PMN was evaluated after 0, 60, 120, and 180 min of co-incubation at 38 °C. SLC-selection increased the proportions of spermatozoa with an intact plasma membrane and low lipid disorder, of spermatozoa with high mitochondrial membrane potential and with high calcium levels, and of progressively motile spermatozoa. In addition, selection through SLC augmented the proportion of phagocytosed spermatozoa, which supported the modulating role of seminal plasma proteins on sperm-PMN interaction. In conclusion, SLC of fresh donkey semen increases the proportions of functionally intact and motile spermatozoa, and appears to remove the seminal plasma proteins that inhibit sperm-PMN binding.

Single Layer Centrifugation with 20% or 30% Porcicoll separates the majority of spermatozoa from a sample without adversely affecting sperm quality

Centrifugation of boar semen through one layer of 40% colloid (Porcicoll) was previously shown to separate spermatozoa from bacteria without having a detrimental effect on sperm quality. However, some spermatozoa were lost. The purpose of the present study was to determine whether 20% or 30% Porcicoll could be used to recover most of the spermatozoa without impacting on sperm quality. Insemination doses (n = 10) from a commercial boar station were sent to the laboratory at the Swedish University of Agricultural Sciences and processed by Single Layer Centrifugation with 20% and 30% Porcicoll approximately 7 hr after semen collection. The resulting sperm samples and controls were evaluated for sperm quality immediately and again after storage at 16-18°C for 4 and 7 days. Sperm recovery was 94 ± 18% and 87 ± 15% for 20% and 30% Porcicoll, respectively (p > .05). Sperm mitochondrial membrane potential and chromatin integrity were unaffected (p > .05). The proportion of live spermatozoa producing superoxide (9 ± 8%, 7 ± 6% and 3 ± 1%; p < .05), and the proportion of spermatozoa with high stainability DNA (0.68 ± 19%, 0.61 ± 0.22% and 0.96 ± 0.23%; p < .05- <0.01), were marginally increased whereas membrane integrity, although high, was lower in the centrifuged samples than in the controls (82 ± 8%, 83 ± 5% versus 92 ± 4%; p < .05). In conclusion, centrifugation through 20% or 30% Porcicoll enables most spermatozoa to be recovered, without having a major effect on sperm quality. These results are encouraging for further studies involving microbiological investigation of the processed samples, and scaling-up to process larger volumes of boar ejaculates.

New protocol to separate llama sperm without enzymatic treatment using Androcoll-E™

The objective of this study was to design a protocol to separate spermatozoa from seminal plasma of raw llama semen without prior enzymatic treatment using a single-layer centrifugation with Androcoll-E^™ (AE). Two experiments were performed: (a) samples were divided into three aliquots (1 ml) that were deposited on the top of 4, 5 or 6 ml of AE and were centrifuged at 800g for 20 min and (b) samples were divided into two aliquots (1 ml) that were deposited on the top of 4 ml of AE and were centrifuged at 600g or 1,000g for 20 min. Columns of 5 and 6 ml of AE showed a total sperm motility (TM) significantly lower, while in the 4 ml column, this parameter was not different from the TM of samples before the AE treatment. The percentage of spermatozoa with intact and functional membranes, normal morphology and intact acrosomes, as well as the percentages of sperm with highly condensed chromatin, was conserved (p ˃ .05) in the three column heights and in the two centrifugation speeds evaluated. In conclusion, the different column heights of AE (4, 5 and 6 ml) and the different centrifugation speeds used (600, 800 and 1,000g) allow separating spermatozoa of raw llama semen without enzymatic treatment, preserving the evaluated sperm characteristics. However, of all the studied treatments, centrifugation in the 4 ml column of AE at 800g would be the method of choice to process raw llama semen samples destined for reproductive biotechnologies.

Colloid centrifugation reduces bacterial load in chilled dog semen

Conventional semen extenders contain antibiotics to prevent bacterial growth. Finding alternatives would be beneficial to minimize the development of bacterial resistance mechanisms. The aim of this study was to determine the effect of Single Layer Centrifugation (SLC) with Canicoll of dog semen on microbial load and sperm quality during cooled storage. Twenty-four ejaculates were obtained from healthy dogs by digital manipulation. Samples were diluted in Tris-citrate-fructose extender without antibiotics and divided into two treatment groups: SLC-selected samples and unselected samples. Sperm motility (CASA), viability and acrosome integrity (PI/FITC-PNA) as well as bacterial load of each microorganism species (colony-forming units/mL) were assessed at 0 and 48 h of storage at 4 °C. Results indicate SLC-selected dog spermatozoa have greater percentages of motility, viability and acrosome integrity (P < 0.05). Bacterial growth in SLC sperm samples was less (P < 0.05) than unselected samples. Removal of individual bacterial species varied from 91 % to 98 % for Escherichia coli (91.62 %), Streptococcus spp. (98.18 %), Staphylococcus spp.(95.33 %) and Pseudomonas spp. (92.50 %). In conclusion, the use of SLC with Canicoll has the potential to decrease bacterial load in chilled dog semen.

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.

Comparison of sperm selection techniques in donkeys: motile subpopulations from a practical point of view

The aim of this study was to compare the post-thaw distribution of motile sperm subpopulations, following simple or colloid centrifugation. A new analysis was used to evaluate the available number of sperm from each subpopulation after each centrifugation protocol. Frozen/thawed semen samples were divided into the following after-thawing treatments: uncentrifuged control (UDC), sperm washing (SW) and two colloid centrifugation procedures (Equipure, SLC-E, and Androcoll, SLC-A). Percentage of total and progressive motility (TM and PM), as well as sperm motility kinematics, distribution of motile sperm subpopulations, and recovery rates, were statistically compared among treatments. The SLC treatments showed higher (P < 0.001) TM and PM than UDC and SW. Following each SLC procedure, different percentages of the subpopulation with the most vigorous and progressive sperm (sP4) were obtained. SLC-A recovered a larger number of sperm belonging to sP4 than SLC-E, but not significantly higher than SW. From a practical point of view, sperm washing, the standard centrifugation procedure for equine semen processing, recovered the same amount of fast and progressive sperm as colloid centrifugation, apparently the best treatment according to traditional analysis. In conclusion, samples processed by SLC have higher motility percentages than SW and UDC but, after combining the available number of sperm, SLC and SW techniques are equally efficient in recovering sperm from the most vigorous, fast and progressive motile subpopulation (sP4).

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.

Treatment of boar sperm with nanoparticles for improved fertility

Continuous progress in nanoscience has allowed the synthesis of various nanoscale particles, known as nanoparticles or nanomaterials which, by harnessing unique physico-chemical properties, are crucial for multiple bio-applications. Despite the revealed toxicity (nanotoxicity) of nanoparticles in various in vitro and in vivo studies, their careful design for biocompatibility and effective interactions with single-celled and multi-cellular organisms has permitted their use in several fields of research and biomedicine. The various nanoparticles synthesized and applied in the veterinary sciences, including reproductive biology, have shown potential to influence routine practices in animal production systems. These include post-collection manipulation of semen and the protection of high-quality spermatozoa to extend their preservation, and to improve sperm-related biotechnologies such as sperm-mediated gene transfer, sperm sorting, sex-sorting, and cryopreservation. Therefore, the application of nanotechnology-based tools to semen may enhance assisted reproductive technologies for biomedical applications and improve economic productivity for farmers. Here, we review the efficacy of available techniques and emerging tools of nanotechnology that might be useful for further selection of high quality boar spermatozoa and productivity improvement.

Nanotechnology-based approach for safer enrichment of semen with best spermatozoa

BACKGROUND

Advances in nanotechnology have permitted molecular-based targeting of cells through safe and biocompatible magnetic nanoparticles (MNP). Their use to detect and remove damaged spermatozoa from semen doses could be of great interest. Here, MNP were synthesized and tested for their ability to target apoptotic (annexin V) and acrosome-reacted (lectin) boar spermatozoa, for high-throughout retrieval in a magnetic field (nanoselection). The potential impacts of nanoselection on sperm functions and performance of offspring sired by sperm subjected to nanoselection were determined. Fresh harvested and extended boar semen was mixed with various amounts (0, 87.5, and 175 μg) of MNP-conjugates (Annexin V-MNP or Lectin-MNP) and incubated (10 to 15 min) for 37 °C in Exp. 1. In Exp. 2, extended semen was mixed with optimal concentrations of MNP-conjugates and incubated (0, 30, 90, or 120 min). In Exp. 3, the synergistic effects of both MNP-conjugates (87.5 μg - 30 min) on spermatozoa was evaluated, followed by sperm fertility assessments through pregnancy of inseminated gilts and performance of neonatal offspring. Sperm motion, viability, and morphology characteristics were evaluated in all experiments.

RESULTS

Transmission electron microscopy, atomic force microscopy, and hyperspectral imaging techniques were used to confirm attachment of MNP-conjugates to damaged spermatozoa. The motility of nanoselected spermatozoa was improved (P < 0.05). The viability of boar sperm, as assessed by the abundance of reactive oxygen species and the integrity of the acrosome, plasma membrane, and mitochondrial membrane was not different between nanoselected and control spermatozoa. The fertility of gilts inseminated with control or nanoselected spermatozoa, as well as growth and health of their offspring were not different between (P > 0.05).

CONCLUSIONS

The findings revealed the benefit of magnetic nanoselection for high-throughput targeting of damaged sperm, for removal and rapid and effortless enrichment of semen doses with highly motile, viable, and fertile spermatozoa. Therefore, magnetic nanoselection for removal of abnormal spermatozoa from semen is a promising tool for improving fertility of males, particularly during periods, such as heat stress during the summer months.

Removal of bacteria from boar semen using a low-density colloid

Antibiotics are added to semen extenders when preparing commercial semen doses for artificial insemination according to national and international guidelines. However, this addition of antibiotics represents non-therapeutic usage and could be contributing to the development of antibiotic resistance. Colloid centrifugation was shown to reduce the load of bacteria present in boar semen and was capable of removing all bacteria if performed directly after semen collection, albeit with some loss of spermatozoa. The present experiment was conducted with a low density colloid to investigate whether it was possible to separate all of the spermatozoa from seminal plasma i.e. without selection for robust spermatozoa, or whether this would have a detrimental effect on sperm quality. Ejaculates from nine boars were extended in Beltsville Thawing Solution without antibiotics and were transported to the laboratory for Single Layer Centrifugation (SLC) on modified Porcicoll i.e. at a low density (S). A further modification was that a sterile inner tube was included inside some of the 50 mL centrifuge tubes to facilitate harvesting of the sperm pellet (M). Aliquots of all samples (control, S and M) were cultured for bacterial quantification and identification using standard microbiological methods. Sperm quality was evaluated daily. Three of the C and M samples and five of the S samples did not contain any bacteria. Mean bacterial counts for the remaining samples (colony forming units/mL) were as follows: C 259 ± 216; S 30 ± 22; M 33 ± 15 (P < 0.01). Citrobacter spp., Staphylococcus simulans, Klebsiella variicola, Escherichia coli, Myroides odoratimimus, Proteus spp. and Enterococcus faecalis were identified in the control samples. There were marginal differences in sperm quality among treatments, with sperm velocity and linearity being higher in S and M samples than in C at all time points. However, sperm viability, capacitation and acrosome status were marginally better in controls than in S or M on day 0, but these differences disappeared during storage. Conclusions: centrifugation through a low density colloid can remove or reduce bacterial contamination in boar ejaculates without using antibiotics. Furthermore, it is possible to collect boar ejaculates without bacterial contamination by paying strict attention to hygiene.

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.

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.

Reproduction biotechnologies in germplasm banking of livestock species: a review

Many biotechnologies are currently used in livestock breeding with the aim of improving reproductive efficiency and increasing the rate of genetic progress in production animals. Semen cryopreservation is the most widely used cryobiotechnology, although vitrification techniques now allow embryos and oocytes to be banked in ever-increasing numbers. Cryopreservation of other types of germplasm (reproductive tissue in general) is also possible, although the techniques are still in the early stages of development for use in livestock species. Although still in their infancy, these techniques are increasingly being used in aquaculture. Germplasm conservation enables reproductive tissues from both animals and fish to be preserved to generate offspring in the future without having to maintain large numbers of living populations of these species. However, such measures need careful planning and coordination. This review explains why the preservation of genetic diversity is needed for livestock and fish, and describes some of the issues involved in germplasm banking. Furthermore, some recent developments in semen handling leading to improved semen cryopreservation and biosecurity measures are also discussed.

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.

Seminal plasma proteins modify the distribution of sperm subpopulations in cryopreserved semen of rams with lesser fertility

Any physiological mechanism involved in sperm selection and semen improvement has effects on heterogeneous sperm populations. This is mainly due to the fact that sperm populations within a single ejaculate have considerable heterogeneity for many variables, such as motility which is meaningful in terms of understanding how some sperm cells possess fertility advantages as compared with other cells. In the present research, initially there was a multivariate and clustering analysis used to assess sperm motility data from cryopreserved ram semen to identify subpopulations and compare the distribution of these clusters between rams with lesser and greater fertility. There were four classifications made of sperm subpopulations (clusters): CL1 fast/linear/progressive sperm; CL2 fast/non-linear sperm; CL3 very fast/linear sperm with vigorous beating and CL4 slow/non-linear sperm. Rams with greater fertility had a lesser proportion of sperm considered as "hyperactivated" (CL2) and a greater proportion of slow and non-linear sperm (CL4) than sperm of rams with lesser fertility. In addition, the effects were assessed for the capacity of seminal plasma (SP) and interacting SP proteins (iSPP) that were present during different seasons of the year to improve the distribution of sperm within subpopulations of semen from rams with lesser fertility. The iSPP and SP were obtained by artificial vagina (AV) and electroejaculation (EE) during breeding and non-breeding seasons and added to thawed semen. All the aggregates had a significant effect on the distribution of sperm subpopulations and effects differed among seasons of the year and depending on collection method used. Even though, future studies are needed to assess the contribution of each subpopulation on ram sperm fertility, it is important that a multivariate analysis be used to evaluate the effect of a treatment on sperm quality variables.

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.

Artificial insemination with frozen-thawed boar sperm

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

Novel agents for sperm purification, sorting, and imaging

The stringent selection of viable spermatozoa ensures the transmission of high-quality genetic material to the egg during fertilization. Sperm heterogeneity within or between ejaculates and between males obliges varied post-collection handling of semen to assure satisfactory fertility rates. The current techniques used to assess sperm generally detect non-viable and non-fertilizing gametes in the ejaculate, but do not permit the investigation of semen for improved fertility outcomes. Advances in technology, however, have spurred the search for new approaches to enrich semen with high-quality spermatozoa and to track intra-uterine sperm migration. This review highlights the current and future methodologies used for sperm labeling, selection, tracking, and imaging, with specific emphasis on the recent influence of nanotechnology.

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.

Single and double layer centrifugation improve the quality of cryopreserved bovine sperm from poor quality ejaculates

Background

Density gradient centrifugation was reported as a technique of semen preparation in assisted reproductive techniques in humans and animals. This technique was found to be efficient in improving semen quality after harmful techniques such as cryopreservation. Recently a modified technique, single layer centrifugation, was proposed as a technique providing a large amount of high quality spermatozoa, and this treatment was performed before conservation. Single layer centrifugation has been studied prevalently in stallions and in boars, but limited data were available for bulls. Occasionally bulls are known to experience a transient reduction in semen quality, thus techniques that allow improvement in semen quality could be applied in this context. The aim of this study was the evaluation of single layer and double layer centrifugation by the use of iodixanol, compared with conventional centrifugation and non-centrifuged semen, on the sperm characteristics during the cryopreservation process in bulls with normal and poor semen quality.

Results

Single layer centrifugation and double layer centrifugation both significantly increased the percentage of normal spermatozoa and decreased the percentage of non-sperm cells in poor quality samples, while both were ineffective in those of normal quality. Sperm characteristics in poor quality samples increased after single layer centrifugation and double layer centrifugation, reaching values similar to those recorded in normal samples, and this trend is maintained after equilibration and after cryopreservation. On the other hand, SLC and DLC resulted in a consistent reduction in the spermatozoa recovered, and this resulted in a reduction of the absolute amount of spermatozoa cryopreserved in the normal samples, without a clear improvement in sperm characteristics in this type of sample.

Conclusions

These data suggested that both SLC and DLC could be performed in practice, but their application should be limited to the cases in which the quality of the spermatozoa recovered is more important than the total amount of spermatozoa.

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.

Porcine semen as a vector for transmission of viral pathogens

Different viruses have been detected in porcine semen. Some of them are on the list of the World Organization for Animal Health (OIE), and consequently, these pathogens are of socioeconomic and/or public health importance and are of major importance in the international trade of animals and animal products. Artificial insemination (AI) is one of the most commonly used assisted reproductive technologies in pig production worldwide. This extensive use has enabled pig producers to benefit from superior genetics at a lower cost compared to natural breeding. However, the broad distribution of processed semen doses for field AI has increased the risk of widespread transmission of swine viral pathogens. Contamination of semen can be due to infections of the boar or can occur during semen collection, processing, and storage. It can result in reduced semen quality, embryonic mortality, endometritis, and systemic infection and/or disease in the recipient female. The presence of viral pathogens in semen can be assessed by demonstration of viable virus, nucleic acid of virus, or indirectly by measuring serum antibodies in the boar. The best way to prevent disease transmission via the semen is to assure that the boars in AI centers are free from the disease, to enforce very strict biosecurity protocols, and to perform routine health monitoring of boars. Prevention of viral semen contamination should be the primary focus because it is easier to prevent contamination than to eliminate viruses once present in semen. Nevertheless, research and development of novel semen processing treatments such as single-layer centrifugation is ongoing and may allow in the future to decontaminate semen.

In vitro fertilization in pigs: New molecules and protocols to consider in the forthcoming years

Assisted reproduction technology (ART) protocols are used in livestock for the improvement and preservation of their genetics and to enhance reproductive efficiency. In the case of pigs, the potential use of embryos for biomedicine is being followed with great interest by the scientific community. Owing to the physiological similarities with humans, embryos produced in vitro and many of those produced in vivo are used in research laboratories for the procurement of stem cells or the production of transgenic animals, sometimes with the purpose of using their organs for xenotransplantation. Several techniques are required for the production of an in vitro-derived embryo. These include in vitro oocyte maturation, sperm preparation, IVF, and further culture of the putative zygotes. Without doubt, among these technologies, IVF is still a critical limiting factor because of the well-known, but still unsolved, question of polyspermy. Despite the improvements made in the past decade, current IVF systems hardly reach 50% to 60% efficiency and any progression in porcine ARTs requires an unavoidable improvement in the monospermy rate. It is time, then, to learn from what happens under in vivo physiological conditions and to transfer this knowledge into ART. This review describes the latest advances in porcine IVF, from sperm preparation procedures to culture media supplements with special attention paid to molecules with a known or potential role in in vivo fertilization. Oviductal fluid is the natural medium in which fertilization takes place, and, in the near future, could become the definitive supplement for culture media, where it would help to solve many of the problems inherent in ARTs in swine and improve the quality of in vitro-derived porcine embryos.

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.

Changes in bull sperm kinematics after single layer centrifugation

The objective of this study was to evaluate bull sperm kinematics after centrifugation through a single layer of a colloid [Single Layer Centrifugation (SLC)]. Ejaculates from 20 bulls were extended and stored at 4-6°C for 24 h during transport to the laboratory for SLC through Androcoll-B, followed by measurement of sperm kinematics in all samples. Total motility (86% and 88% for uncentrifuged and SLC samples, respectively) and progressive motility (84% for both the groups) were similar (p > 0.05). In contrast, straightness (STR) (0.65 vs 0.69), linearity (LIN) (0.32 vs 0.35) and beat cross frequency (BCF) (22.3 vs 23.6 Hz) were significantly higher in the SLC-selected samples than in the uncentrifuged samples, whereas velocity of the average path (VAP) (95 vs 90 μm/s), curvilinear velocity (VCL) (192 vs 180 μm/s), amplitude of lateral head deviation (ALH) (7 μm vs 6.5 μm) and hypermotility (49% vs 38%) were significantly decreased. The kinematics of the samples with the poorest motility was improved most by SLC. In conclusion, even though SLC had no direct effect on total and progressive motility, it appeared to have a positive influence on several other kinematic parameters that may be important for fertilization after artificial insemination.

Quality of bull spermatozoa after preparation by single-layer centrifugation

The present study aimed to evaluate the effect of single-layer centrifugation (SLC) through a species-specific colloid (Androcoll-B; patent pending, J. M. Morrell) on bull sperm quality. Computer-assisted sperm analysis of motility and flow cytometric analysis of sperm viability (SYBR-14/propidium iodide staining), chromatin integrity (acridine orange staining), reactive oxygen species production [Hoechst 33258-hydroethidine-2',7'-dichlorodihydrofluorescein diacetate (HO-HE-DCFDA) staining], mitochondrial membrane potential (staining with JC-1 probe), and protein tyrosine phosphorylation (specific antibody staining) were performed on unselected and SLC-selected sperm samples. Single-layer centrifugation of bull spermatozoa resulted in the selection of a sperm population that had high mitochondrial membrane potential, a higher content of phosphorylated protein, and more reactive oxygen species than control samples. Sperm chromatin damage was lower in the SLC samples although sperm viability and motility did not differ between SLC samples and controls. These observations suggest that SLC of bull semen in a soybean-containing extender improved some, but not all, parameters of sperm quality.