Single Layer Centrifugation Can Be Scaled-Up Further to Process up to 150 mL Semen

Antibiotics in semen extenders - a multiplicity of paradoxes

Addition of antibiotics to semen extenders was taken for granted for many years, from the time that commercial artificial insemination in livestock first began many decades ago. However, there is now a growing realisation that this non-therapeutic utilisation of antibacterial agents is contrary to current recommendations for prudent use that medical and veterinary professionals are advised to follow. Furthermore, antibiotics are not benign, having negative effects on sperm samples, the inseminated female, personnel and potentially the environment. The purpose of this review is three-fold: to highlight the fact that antibiotics are used in semen extenders, with the result that considerable amounts are used globally in animal breeding, to review recent studies on the negative aspects of using antibiotics for this purpose, and to look at possible alternatives. Recent changes in the legislation regarding semen extenders occurred in some, but not all, countries, leaving question marks for semen producers as to whether antibiotics should be added to semen extenders or not.

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.

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.

Antibiotics and their alternatives in Artificial Breeding in livestock

Antibiotics are mandatory components of semen extenders for the control of bacterial contamination and growth. The increasing rate of worldwide resistance to conventional antibiotics in semen preservation media requires the development of new antimicrobial alternatives. This review provides an update on this topic and also highlights the improvement of hygiene in Artificial Insemination centers in order to prevent the development of bacterial resistance. Ideas are shared on future diagnostic tools for bacterial contamination in Artificial Breeding. Finally, new methods to remove or reduce bacteria in semen will be discussed.

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.

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.

Effects of single layer centrifugation (SLC) on bull spermatozoa prior to freezing on post-thaw semen characteristics

Single layer centrifugation (SLC) has been shown to select the most robust spermatozoa from the ejaculate in several species. Here the effects of SLC prior to freezing on various parameters of frozen-thawed bovine sperm quality are reported. Semen from 8 bulls was layered on top of a species-specific colloid, Bovicoll. After centrifugation for 20 min at 300 g, the resulting sperm pellet was resuspended in OPTIXcell^® (IMV Technologies, l'Aigle, France); the SLC-selected sperm samples and uncentrifuged controls were frozen. On thawing, all sperm samples were analysed for membrane integrity, production of reactive oxygen species, mitochondrial membrane potential (MMP) and chromatin integrity. The SLC-treated samples had a higher percentage of live, superoxide-positive spermatozoa than uncentrifuged samples (27.9 ± 5.1% versus 21.7 ± 6.7%; p = .03). They had a higher proportion of spermatozoa with high mitochondrial membrane potential than uncentrifuged samples (55.9 ± 8.2% versus 40.5 ± 15.1%; p = .03) and also a lower proportion of spermatozoa with low mitochondrial membrane potential than non-treated samples (42.0 ± 8.5% versus 55.9 ± 14.4%; p = .04). No significant effects of treatment were found for membrane integrity or chromatin integrity. The effect of bull was significant on the proportions of dead, superoxide-positive spermatozoa and live, hydrogen peroxide-negative spermatozoa, as well as on membrane integrity, but it was not significant for mitochondrial membrane potential or chromatin integrity. These results suggest that SLC selects the most metabolically active bull spermatozoa from the rest of the population in normal ejaculates; the pattern of reactive oxygen species production may be different in SLC-selected spermatozoa compared to unselected samples.

Alternatives to antibiotics in semen extenders: a review

Antibiotics are added to semen extenders to be used for artificial insemination (AI) in livestock breeding to control bacterial contamination in semen arising during collection and processing. The antibiotics to be added and their concentrations for semen for international trade are specified by government directives. Since the animal production industry uses large quantities of semen for artificial insemination, large amounts of antibiotics are currently used in semen extenders. Possible alternatives to antibiotics are discussed, including physical removal of the bacteria during semen processing, as well as the development of novel antimicrobials. Colloid centrifugation, particularly Single Layer Centrifugation, when carried out with a strict aseptic technique, offers a feasible method for reducing bacterial contamination in semen and is a practical method for semen processing laboratories to adopt. However, none of these alternatives to antibiotics should replace strict attention to hygiene during semen collection and handling.

Colloid centrifugation selects normal spermatozoa from polymorphic bull ejaculates: a case study

Semen from a Western Finncattle bull exhibiting a highly polymorphic spermiogram was processed by colloid centrifugation using Androcoll-B, a species-specific silane-coated silica colloid. In the first experiment, Single Layer Centrifugation (SLC) was used to identify which density colloids were needed to separate different cell populations. Colloids of the two chosen densities were then used in a density gradient resulting in two sperm subpopulations, one containing nearly all normally sized spermatozoa and the other enriched for the macrocephalic spermatozoa. Microcephalic spermatozoa did not appear in either of the selected subpopulations. Using a combination of SLC and DGC with this species-specific colloid, it was possible to separate the spermatozoa into different subpopulations, that is, a subpopulation containing nearly all normally sized spermatozoa, and another one enriched for the macrocephalic spermatozoa. Thus, colloid centrifugation could be used to select sufficient normal spermatozoa from a highly polymorphic ejaculate for AI, if desired.