Development of the genital microflora in stallions used for artificial insemination throughout the breeding season

Bacterial diversity in semen from stallions in three European countries evaluated by 16S sequencing

The microbiome plays a significant role in shaping the health and functioning of the systems it inhabits. The seminal microbiome of stallions has implications for the health of the reproductive tract, sperm quality during preservation and antibiotic use in semen extenders. Diverse bacteria are present on the external genital tract and a mix of commensal microorganisms populates various parts of the reproductive tract, influencing the seminal bacterial content. Other sources of bacteria include the environment, semen collection equipment, and personnel. The bacterial load can adversely affect sperm quality and fertility, particularly in artificial insemination, where semen is extended and stored before use. Antibiotics are frequently used to inhibit bacterial growth, but their effectiveness varies depending on the bacterial strains present. The aim of this study was to assess the bacterial diversity in semen from 37 healthy stallions across three European nations (Germany, Portugal, and Sweden) using 16S sequencing. Semen samples were collected from individual stallions at three AI centers; DNA extraction, sequencing, and bioinformatic analysis were performed. Differences in bacterial diversity among the stallions were seen; although bacterial phyla were shared across the regions, differences were observed at the genus level. Climate, husbandry practices, and individual variability likely contribute to these differences. These findings underscore the importance of tailoring antibiotic strategies for semen preservation based on regional bacterial profiles. The study presents a comprehensive approach to understanding the intricacies of the stallion seminal microbiome and its potential implications for reproductive technologies and animal health.

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.

Strategies to Reduce the Use of Antibiotics in Fresh and Chilled Equine Semen

The study assessed the impact of four equine semen processing techniques on sperm quality and microbial load immediately post-processing and after 48 h of refrigeration. The aim was to explore the potential reduction of prophylactic antibiotic usage in semen extenders. Semen from ten adult stallions was collected and processed under a strict hygiene protocol and divided into four aliquots: Simple Centrifugation with antibiotics (SC+), Simple Centrifugation (SC-), Single-Layer Colloidal Centrifugation (CC-), and Filtration (with SpermFilter®) (F-), all in extenders without antibiotics. Sperm motility, viability, and microbial load on three culture media were assessed. No significant differences were observed in the main in the sperm quality parameters among the four protocols post-processing and at 48 h (p < 0.05 or p < 0.1). Microbial loads in Columbia 5% Sheep Blood Agar and Schaedler vitamin K1 5% Sheep Blood Agar mediums were significantly higher (p < 0.10) for raw semen than for CS+, CC-, and F- post-processing. For Sabouraud Dextrose Agar medium, the microbial load was significantly higher (p < 0.10) in raw semen compared to CS+ and F-. No significant differences (p < 0.10) were found in 48 h chilled samples. Regardless of antibiotic presence, the evaluated processing methods, when combined with rigorous hygiene measures, maintained semen quality and reduced microbial load to the same extent as a traditional protocol using antibiotics.

Clinical Aspects of Bacterial Distribution and Antibiotic Resistance in the Reproductive System of Equids

Antibiotic administration is a standard therapeutic practice for the treatment of reproductive disorders of equids. This might lead to undesirable microbial imbalance and could favour the acquisition of antibiotic resistance. Therefore, it is imperative for clinicians to understand patterns of antibiotic resistance when considering and developing treatment regimes. Continued engagement of clinicians with novel alternative approaches to treat reproductive infections would be essential in order to address this rising threat within the One Health perspective. The objectives of the present review were to present the bacterial infections in the reproductive system of equids (horses, donkeys), to upraise the literature related to the issue of antibiotic resistance of bacteria causing these infections and to discuss the topic from a clinical perspective. Initially, the review summarised the various infections of the reproductive system of equids (genital system of females, genital system of males, mammary glands) and the causal bacteria, providing relevant information about horses and donkeys. Subsequently, the clinical therapeutics of these infections were presented, taking into account the significance of antibiotic resistance of bacteria as a limiting factor in treating the infections. Finally, approaches to circumvent antibiotic resistance in clinical settings were summarized. It was concluded that awareness regarding antibiotic resistance in equine reproductive medicine would increase, as we would recognise the multifaceted problem of resistance. Actions and initiatives within the One Health approach, minimizing the potential dissemination of resistant strains to humans and to the environment, with specific applications in medicine of equids should be appropriately instituted internationally.

Effect of Some Plant-Based Substances on Microbial Content and Sperm Quality Parameters of Bull Semen

The rapid emergence of antibacterial resistance requires alternatives to antibiotics to be found, including for semen preservation. One of the possible alternatives would be to use plant-based substances with known antimicrobial effects. The objective of this study was to test the antimicrobial effect of pomegranate powder, ginger, and curcumin extract in two concentrations on bull semen microbiota after exposure for <2 h and 24 h. An additional aim was to evaluate the effect of these substances on sperm quality parameters. The bacterial count in semen was low from the beginning; however, a reduction was present for all tested substances compared with control. A reduction in bacterial count in control samples was also observed with time. Curcumin at a concentration of 5%, reduced bacterial count by 32% and was the only substance that had a slight positive effect on sperm kinematics. The other substances were associated with a decline in sperm kinematics and viability. Neither concentration of curcumin had a deleterious effect on sperm viability parameters measured by flow cytometry. The results of this study indicate that curcumin extract at a concentration of 5% can reduce the bacterial count and does not have a negative influence on bull sperm quality.

Penicillin and amikacin mixture has bactericidal activity equivalent to gentamicin, tylosin, lincomycin and spectinomycin mixture in equine frozen semen

Neat stallion semen can contain a variety of microorganisms, some of which may impair sperm quality and/or cause infection of the mares' reproductive tract. For this reason, antibiotics are commonly added to semen extenders. A combination of gentamicin, tylosin, lincomycin and spectinomycin (GTLS) has been recommended for use, but there are no reports on the use of this mixture in equine semen extender. Penicillin and amikacin (PA) are safe for preserving sperm quality while effectively controlling bacterial growth in equine cooled stored semen, but data on frozen semen are scarce. Therefore, a bioequivalence study was performed to assess the bactericidal activity of GTLS and PA in equine frozen semen. Nine mature, healthy stallions were used in the study. Split ejaculates were processed using media without antibiotics (Control) or with different antibiotics. For the GTLS group, centrifugation medium and freezing extender were prepared with gentamicin 250 μg/ml, tylosin 50 μg/ml, lincomycin 150 μg/ml and spectinomycin 300 μg/ml. For the PA group, the centrifugation medium was prepared with potassium penicillin G (PPG) 1200 units/ml and the freezing extender was prepared with PPG 1200 units/ml and amikacin 500 μg/ml. Semen processed in extenders without antibiotics had higher (p < .005) bacterial loads throughout all cryopreservation processing steps than semen samples processed using antibiotics. There were no differences in semen bacterial load after centrifugation, 15 and 30 min after final extension, and after thawing between GTLS and PA groups, but PA had faster (p < .05) kill-time kinetics than GTLS. Only minor differences in sperm kinetic parameters were observed among groups. In conclusion, this study demonstrated bioequivalence between GTLS and PA in mitigating end-point bacterial loads. Prudent concentrations of the antibiotic mixtures evaluated in this study can be considered both effective and sperm-safe for equine frozen semen.

The Semen Microbiome and Semen Parameters in Healthy Stallions

Simple Summary

Stallion infertility is a major cause of concern in the horse industry. Despite zootechnics advances, sub- or infertile animals appear in stud farms without a toxic, genetic, or nutritional reason. Recent research in human andrology has opened the door for a new, plausible factor that affects sperm quality: seminal microflora. In recent years, there has been an increasing amount of evidence regarding the relationship between different seminal flora compositions and male fertility. However, little has been studied in veterinary science, including horses. Therefore, the objective of this study was to examine associations with the presence of bacteria families in horse semen with five sperm quality parameters: concentration, total number of spermatozoa, total and progressive sperm motility, and DNA fragmentation. Our study detected a correlation between the presence of the Peptoniphilaceae family and higher total motility and the presence of Clostridiales Incertae Sedis XI and lower progressive motility. These changes in seminal flora may contribute to the idiopathically poorer sperm quality in certain animals. Although further mechanisms behind bacteria–spermatozoa interactions are unknown, these associations are already leading to a new therapeutic approach to infertility: the use of prebiotics, which has already yielded promising results in human andrology.

Abstract

Despite the advances in reproductive technology, there is still a considerable number of low sperm quality cases in stallions. Recent studies in humans have detected several seminal microflora–spermatozoa associations behind some idiopathic infertility cases. However, no studies are available on horses, and there is limited information on the microflora present in stallion ejaculates. Accordingly, the objective of this study was to examine associations to the presence of bacteria families with five sperm quality parameters: concentration, total number of spermatozoa, total and progressive motility, and DNA fragmentation. Samples were cryopreserved after their extraction. High-speed homogenization using grinding media was performed for cell disruption. Family identification was performed via 16S rRNA sequencing. Bacterial families were only considered if the relative abundance was higher than 1%. Only two families appeared to have a correlation with two sperm quality parameters. Peptoniphilaceae correlated positively with total sperm motility, whereas Clostridiales Incertae Sedis XI correlated negatively with progressive motility. No significant differences were found for the rest of the parameters. In conclusion, the seminal microbiome may affect spermatozoa activity. Our findings are based on statistical associations; thus, further studies are needed to understand the internal interactions between seminal flora and cells.

Antimicrobial Resistance in Equine Reproduction

Bacteria develop resistance to antibiotics following low-level "background" exposure to antimicrobial agents as well as from exposure at therapeutic levels during treatment for bacterial infections. In this review, we look specifically at antimicrobial resistance (AMR) in the equine reproductive tract and its possible origin, focusing particularly on antibiotics in semen extenders used in preparing semen doses for artificial insemination. Our review of the literature indicated that AMR in the equine uterus and vagina were reported worldwide in the last 20 years, in locations as diverse as Europe, India, and the United States. Bacteria colonizing the mucosa of the reproductive tract are transferred to semen during collection; further contamination of the semen may occur during processing, despite strict attention to hygiene at critical control points. These bacteria compete with spermatozoa for nutrients in the semen extender, producing metabolic byproducts and toxins that have a detrimental effect on sperm quality. Potential pathogens such as Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa may occasionally cause fertility issues in inseminated mares. Antibiotics are added during semen processing, according to legislation, to impede the growth of these microorganisms but may have a detrimental effect on sperm quality, depending on the antimicrobial agent and concentration used. However, this addition of antibiotics is counter to current recommendations on the prudent use of antibiotics, which recommend that antibiotics should be used only for therapeutic purposes and after establishing bacterial sensitivity. There is some evidence of resistance among bacteria found in semen samples. Potential alternatives to the addition of antibiotics are considered, especially physical removal separation of spermatozoa from bacteria. Suggestions for further research with colloid centrifugation are provided.

Characterization of the seminal bacterial microbiome of healthy, fertile stallions using next-generation sequencing

High-throughput sequencing studies have shown the important role microbial communities play in the male reproductive tract, indicating differences in the semen microbial composition between fertile and infertile males. Most of these studies were made on human beings but little is known regarding domestic animals. Seminal bacteria studies made in stallions mostly focus on pathogenic bacteria and on their impact on reproductive technology. However, little is known about stallion commensal seminal microflora. That ultimately hinders our capacity to associate specific bacteria to conditions or seminal quality. Therefore, the aim of this study was to characterize the seminal microbial composition of 12 healthy, fertile stallion using next-generation sequencing. Hypervariable region V3 was chosen for bacterial identification. A total of nine phyla was detected. The most abundant ones were Bacteroidetes (46.50%), Firmicutes (29.92%) and Actinobacteria (13.58%). At family level, we found 69 bacterial families, but only nine are common in all samples. Porphyromonadaceae (33.18%), Peptoniphilaceae (14.09%), Corynebacteriaceae (11.32%) and Prevotellaceae (9.05%) were the most representative ones, while the Firmicutes phylum displayed the highest number of families (23, a third of the total). Samples showed high inter-subject variability. Findings previously described in other species notably differ from our findings. Families found in human such as Lactobacillaceae, Staphylococcaceae and Streptococcaceae only represented a 0.00%, 0.17% and 0.22% abundance in our samples, respectively. In conclusion, Porphyromonadaceae, Prevotellaceae, Peptoniphilaceae and Corynebacteriaceae families are highly represented in the seminal microbiome of healthy, fertile stallions. A high variation among individuals is also observed.

Microbiota of semen from stallions in Sweden identified by MALDI-TOF

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Bacteria isolated from stallion semen vary in number and species found.

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Differences may depend on culture conditions and method of identification.

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64% bacteria in stallion semen were cultured and identified by MALDI-TOF.

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The number of bacteria varied considerably among samples, even from the same stud.

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More information is needed on their effect on sperm quality.

Stallion semen is known to contain environmental bacteria and normal commensals, and in some cases may contain opportunistic pathogens. These bacteria may negatively influence sperm quality during storage before artificial insemination. The bacteria isolated depend on the culture conditions and method of identification; therefore, the aim of this study was to identify as many of the bacteria present in stallion semen as possible by culturing aliquots of semen under a variety of conditions. Eleven semen samples were available: five extended semen samples from one stud together with a sample of the extender, and six raw semen samples from another stud. Aliquots of semen samples were cultured on different agars and under specialized conditions; individual bacterial colonies were identified using Matrix-assisted laser desorption ionization time of flight mass spectrometry. Approximately 55% of the bacteria could be identified, with 20 bacterial taxa being isolated from semen samples from the five stallions on the first stud and 11 taxa from the semen samples from six stallions on the second stud. Staphylococcus spp. were present in all samples, and Micrococcus spp. were present in all of the extended semen samples although they were also isolated from the extender. The number of bacteria in colony forming units per mL varied considerably among samples. Only one microbe known to be associated with equine infertility, Pseudomonas spp., was isolated from three samples, albeit in low numbers. In conclusion, bacterial culture followed by MALDI-TOF does not identify all bacteria present in stallion semen samples. In-depth knowledge of which microbes are likely to be present is useful in determining their effects on sperm quality and, where appropriate, developing protocols for effectively controlling microbial growth.

Inclusion of supplemental antibiotics (amikacin - penicillin) in a commercial extender for stallion semen: Effects on sperm quality, bacterial growth, and fertility following cooled storage

In this study, the effectiveness of supplementing INRA-96® extender (INRA-Control; original antibiotic formulation: potassium penicillin G = 38 μg/mL; gentamicin sulfate = 105 μg/mL; amphotericin B = 0.315 μg/mL) with amikacin sulfate and potassium penicillin G (AP) was determined. In Exp. 1, two sources of amikacin (INRA-AP-Sigma or INRA-AP-GoldBio) in combination with penicillin G were compared with ticarcillin/clavulanate (INRA-Tim) or no-supplemental antibiotics (INRA-Control) to examine effects on sperm quality and commensal bacterial growth. No differences were detected in semen quality among treatments after 30 min of exposure (Time 30min) or 24 h of cooled storage (Time 24 h; P > 0.05). At both time periods, commensal bacterial growth was significantly lower in Groups INRA-AP-GoldBio and INRA-AP-Sigma than in INRA-Tim or INRA-Control (P < 0.05). In Exp. 2, increasing doses of amikacin sulfate (GoldBio) plus potassium penicillin G (Sigma) - AP (AP-1000, 2000, 3000, 4000 or 5000 μg-IU/mL, respectively) were added to INRA-96® extender and their effects on sperm quality and commensal bacterial growth were evaluated at Time 30min and Time 24 h. Slight reductions in progressive motility and viability were observed at Time 30min in Groups AP-4000 and AP-5000 as compared to other treatment groups (P < 0.05); however, no differences in sperm quality were detected among treatment groups at Time 24 h (P > 0.05). At both time periods, commensal bacterial growth was significantly lower in Groups AP-3000, AP-4000 and AP-5000 than in AP-1000 and AP-2000 (P < 0.05). In Exp. 3, a breeding trial was conducted to determine the effect of adding a high dose of AP (AP-5000) to INRA-96® extender on resulting pregnancy rates of mares bred with cool-stored semen (Time 24 h). Numerical, but not statistical differences, were observed in pregnancy rates between the mares bred with INRA-Control (6/11; 55%) or INRA-AP-5000 (9/11; 82%; P > 0.05). Supplementation of INRA-96® extender with two different concentrations of AP (AP-1000 or AP-5000) was tested in two clinical cases of stallions where semen was moderately to heavily contaminated with Pseudomonas aeruginosa, or both Klebsiella pneumoniae and Pseudomonas aeruginosa. In both cases, addition of AP resulted in a considerable decrease on bacterial growth in cool-stored semen when compared to the use of the original INRA-96® extender without supplemental antibiotics. In conclusion, the addition of amikacin sulfate and potassium penicillin G to INRA-96® extender allowed for effective control of commensal bacteria without affecting sperm quality. Higher doses of amikacin and penicillin can be safely added to INRA-96® extender to improve the antibacterial activity of this extender against commensal, and potentially pathogenic bacteria, while sperm quality and fertility of cooled semen remains unaffected. Based on the results of the present study, we currently recommend that INRA-96® extender can be safely supplemented with amikacin/penicillin by using a conventional dose of 1000 μg/mL - 1000 IU/mL as a prophylactic measure in cases where contamination of the ejaculates with commensal bacteria is evident. Alternatively, a high dose (5000 μg/mL - 5000 IU/mL) can be used as a control method for potentially pathogenic bacteria.

Metagenomic analysis of bacteria in stallion semen

Bacteria colonize stallion semen during collection and processing which may cause disease in inseminated females or negatively affect sperm quality during storage prior to insemination. Antibiotics are added to semen extenders to control the growth of these bacteria but may induce antimicrobial resistance. Research into alternatives to antibiotics for this purpose requires knowledge of which bacteria are present in semen. Not all bacteria in semen, however, can be identified by conventional microbiological techniques. The objectives of the study were to: i) determine which bacteria are present in stallion semen using metagenomics; and ii) investigate individual differences in bacterial content in semen from all stallions on one premises. Bacterial DNA was extracted from ejaculates from seven stallions (one ejaculate per stallion) and bacteria were identified using 16S sequencing. In total, 83 bacterial genera were identified, varying from 25 to 52 among different individuals. There was a negative correlation (r = -0.81212; P <  0.05) between the presence of Treponema spp. and Advenella spp. In conclusion, most of the bacteria present in stallion semen could be identified to genus level by 16S sequencing even when present at a low frequency. This method of identification may help to clarify individual variation in bacterial content and its potential effects on fertility.

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.

Bacteria detected in the genital tract, semen or pre-ejaculatory fluid of Swedish stallions from 2007 to 2017

Background

Although artificial insemination (AI) was developed as a means of controlling disease transmission, pathogens can still be transmitted to females in semen used for AI. In addition, bacteria can cause deterioration in sperm quality during storage. Semen becomes contaminated by the male’s normal bacterial flora as it passes out of the reproductive tract but potential pathogens may also contaminate the semen. Therefore, semen samples from stallions to be used for AI are tested before the breeding season to minimize transmission of pathogens to inseminated mares. In Sweden, semen samples are tested at the National Veterinary Institute, Uppsala (SVA). For the present study, a retrospective analysis was made of potentially pathogenic bacteria isolated from samples submitted to the SVA from 2007 to 2017.

Results

In our study, Taylorella equigenitalis was found infrequently (53 out of 25,512 samples), representing 11 out of 2308 stallions. If T. equigenitalis was detected, the stallions were treated with antibiotics and re-tested later in the same year. Klebsiella pneumoniae and beta haemolytic streptococci were the most commonly found potential pathogens, whereas Pseudomonas aeruginosa was also isolated occasionally. There were considerable differences in the number of species isolated each year.

Conclusions

Potential pathogens were identified in relatively few of the samples submitted to SVA during this period, with T. equigenitalis not being identified since 2015. Of the other potential pathogens, K. pneumoniae and beta haemolytic streptococci were the most common. The information is relevant for determining guidelines on the testing and treatment of stallions before breeding.

Effect of presence or absence of antibiotics and use of modified single layer centrifugation on bacteria in pony stallion semen

Bacteria contaminate semen during collection and handling. The objective of this study was to identify the bacteria in pony stallion semen, the effects of antibiotics included in commercial semen extenders (lincomycin and spectinomycin) and the effect of modified single layer centrifugation (MSLC), on bacterial load. Ejaculates from six pony stallions, 3 ejaculates per animal, were extended in EquiPlus extender either with or without antibiotics. Aliquots were processed by MSLC to form four treatment groups: control and MSLC with antibiotics (CA and SA, respectively) and control and MSLC without antibiotics (CW and SW, respectively). Bacteriological examinations were carried out within 2 hr. Thirty-one species of bacteria were isolated from one or more ejaculates, with Corynebacterium spp. being the most frequently detected. Corynebacterium spp. were present in all ejaculates. The MSLC resulted in a significantly lower total bacterial count than controls (CA vs. SA, p < 0.001; CW vs. SW, p < 0.0001).

How does the microbial load affect the quality of equine cool-stored semen?

Contaminating bacteria present in stallion ejaculates may compromise sperm quality during storage. Different procedures have been used to reduce the load of microorganisms in semen and avoid bacterial growth during storage. The aims of this study were: 1) to evaluate different techniques to eliminate bacteria in semen 2) to study the relationship between total microflora load (TML) and ROS production; and 3) to determine if TML affects the functionality of cool-stored sperm. Ejaculates from 11 stallions were split and processed in 3 ways: A. extended semen; B. conventional centrifuged semen, and C. Single layer centrifugation through Androcoll-E (SLC). All samples were preserved in INRA 96 at 5 °C for 72 h. Aliquots from native semen and from different treatments were taken for bacteriological analysis at T0, T24, T48 and T72h of storage and Total microbial load (TML: CFU (colony-forming units/ml) was calculated. The ROS production (dichlorodihydrofluorescein diacetate for H₂O₂, dihydroethidium for superoxide anion and CellROX deep red for total ROS), viability (YO-PRO-1-Ethidium) and lipid peroxidation (BODIPY-C11) were assessed by flow cytometry, and motility by CASA. The bacteria isolated were Corynebacterium spp, Arcanobacterium spp, Bacillus spp, Dermobacter, Staphylococcus spp, Streptococcus spp, Penicilium spp. TML of semen showed correlations with live sperm (r: -0.771), dead sperm (r: 0.580), H₂O₂ production (r: 0.740), and total ROS production (CellROX (+)) (r: -0.607), Total motility (r: 0.587), Progressive motility (r: -0.566), VCL (r: -0.664), VSL (r: -0,569), VAP (r: -0.534) (p ≤ 0.05). SLC removed 99.34% of the microbial load, which was assicated with a significanlty reduced H₂O₂ production (p ≤ 0.05). However, only samples treated with Androcoll-E had a higher total ROS production (CellROX +) (p ≤ 0.05). These results suggest that CellROX stain probably identifies superoxide production rather than H₂O₂ and this higher superoxide production may reflect an intense sperm functionality. The bacterial load increased the production of H₂O₂ in cool-stored semen which was associated with lower tolerance to refrigeration. SLC was the sperm processing technique that was most efficient at removing bacteria, reducing H₂O₂ production and selecting the most functional sperm.

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 of fresh stallion semen before cryopreservation decreased microorganism load of frozen-thawed semen without affecting seminal kinetics

Freezability of equine semen may be influenced by microorganism population of semen. The objective of this study was to verify the effect of single-layer density gradient centrifugation (SLC) of fresh semen before cryopreservation on semen's microbial load (ML) and sperm cells kinetics after freezing-thawing. For that, one ejaculate was collected from 20 healthy stallions and split into control (C) samples (cryopreserved without previous SLC) and SLC samples (subjected to SLC). Semen cryopreservation was performed according to the same protocol in both groups. Microbial load of each microorganism species and total microbial load (TML) expressed in colony-forming units (CFU/mL) as well as frozen-thawed sperm kinetics were assessed in both groups. Additional analysis of the TML was performed, subdividing the frozen-thawed samples in "suitable" (total motility ≥ 30%) and "unsuitable" (total motility < 30%) semen for freezing programs, and comparing the C and SLC groups within these subpopulations. After thawing, SLC samples had less (P < 0.05) TML (88.65 × 10(2) ± 83.8 × 10(2) CFU/mL) than C samples (155.69 × 10(2) ± 48.85 × 10(2) CFU/mL), mainly due to a reduction of Enterococcus spp. and Bacillus spp. A relationship between post-thaw motility and SLC effect on ML was noted, as only in samples with more than 30% total motility was ML reduced (P < 0.05) by SLC (from 51.33 × 10(2) ± 33.26 × 10(2) CFU/mL to 26.68 × 10(2) ± 12.39 × 10(2) CFU/mL in "suitable" frozen-thawed semen vs. 240.90 × 10(2) ± 498.20 × 10(2) to 139.30 × 10(2) ± 290.30 × 10(2) CFU/mL in "unsuitable" frozen-thawed semen). The effect of SLC on kinetics of frozen-thawed sperm cells was negligible.

The effects of antibiotic additions to extenders on fresh and frozen-thawed bull semen

Reproduction in dairy cows is based around the use of cryopreserved semen. Antibiotics are utilized to control bacterial contamination and growth in cryopreserved bull semen. The antibiotic resistance of some bacteria required the evaluation of new antibiotic combinations with a high level of antibacterial effectiveness and a negligible effect on spermatozoa. In this research, we studied the effect of the fluorinate carboxyquinolone ofloxacin and the combination of ceftiofur/tylosin on bull spermatozoa and in-field bacterial growth. In Experiment 1, the toxicity of different levels of ofloxacin and ceftiofur/tylosin was tested by the incubation of bull spermatozoa and the evaluation of sperm kinetic parameters, membranes and acrosome integrity after dilution, and at 60 and 120 min after incubation. The data reported in this study reveals that both antibiotic combinations, at all concentrations, seem to have a negligible effect on spermatozoa with respect to all of the parameters examined (p>0.05). Furthermore, progressive motility was significantly higher for sperm diluted with both antibiotic combinations compared with samples without antibiotics (p<0.01). In Experiment 2, the ability of ofloxacin or ceftiofur/tylosin to control bacterial growth during bovine semen cryopreservation was compared with the combination of gentamicin/tylosin/spectinomycin/lincomycin. A significant reduction in progressive motility was found in cooled semen with respect to all of the antibiotic treatments (p<0.05). However, the membrane integrity was found to significantly rise in frozen samples with, compared to samples without, antibiotics (p<0.05). In a bull, gentamicin, tylosin, spectinomycin, and lincomycin failed to control bacterial growth in the cryopreserved sample, while no such growth was found in samples extended with ceftiofur/tylosin or ofloxacin. In conclusion, both ceftiofur/tylosin and ofloxacin can be safely added to bull seminal extenders, and both can protect insemination doses from bacteria that are resistant to other antibiotic combinations.