Reduced bacterial load in stallion semen by modified single layer centrifugation or sperm washing

The presence of bacteria poses a significant challenge to the quality of stallion semen used in artificial insemination. The bacterial content of insemination doses arises from various sources, such as the healthy stallion, environment, and collection equipment, and is implicated in fertility problems as well as reduced sperm quality during storage. The conventional approach of adding antibiotics to semen extenders raises concerns about antimicrobial resistance and potential negative effects on sperm characteristics, and may not be effective in inhibiting all bacteria. The objective of this study was to determine whether an innovative alternative to antibiotic usage - centrifugation through a single layer of a low density colloid (SLC) - could reduce the bacterial load in stallion semen, and to compare sperm characteristics in samples arising from this procedure, or simple extension of the ejaculate in semen extender, or from sperm washing, i.e. adding extender and then centrifuging the sample to allow the removal of most of the seminal plasma and extender. Eighteen semen samples were collected from six stallions. The semen samples were split and extended prior to washing or SLC, or received no further treatment other than extension. After preparation aliquots from each type of sample were sent for bacteriological examination; the remaining samples were stored for up to 72 h, with daily checks on sperm quality. The low density colloid SLC outperformed sperm washing or extension for bacterial reduction, effectively removing several bacterial species. The bacterial load in the samples was as follows: extended semen, 16 ± 6.7 × 105; washed, 5.8 ± 2.0 × 105; SLC, 2.3 ± 0.88 × 105, p < 0.0001. In addition, SLC completely removed some bacterial species, such as Staphylococcus xylosus. Although there is no selection for robust spermatozoa with the low density colloid, sperm motility, membrane integrity, and DNA fragmentation were not different to washed sperm samples. These findings suggest that SLC with a low density colloid offers a promising method for reducing bacterial contamination in stallion semen without resorting to antibiotics.

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.

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.

Bacteria in the healthy equine vagina during the estrous cycle

An understanding of the normal bacterial microbiota of any organ is essential to provide the background to conditions and interventions that might cause the microbiota to change. In the vagina of the mare, a change of bacterial microbiota could be induced by introduction of semen, treatment with antibiotics, discharge from an unhealthy uterus etc. Previous studies on equine vaginal bacteria are not all conducted in the same way and results are not altogether consistent. Therefore, this study was designed to provide a deeper understanding of the bacterial microbiota of the mare vagina, and possible changes throughout the estrous cycle. The cranial portion of the vagina was sampled on day 0 (ovulation), day 3, day 7, and day 14 of the estrous cycle. The vaginal sampling was conducted with double-guarded occluded swabs from the cranial floor of the vagina. Ovulation was determined by rectal palpation and ultrasonic examination, and the day 0 samples were taken within ±24 h of ovulation. Swabs were brought to the laboratory in Amies medium within 2-3 h and were plated out immediately on both selective and non-selective agars. Results were registered as amount of growth (qualitatively), bacterial species and number of isolates. Bacterial growth was highest on day 3 and 7, representing the beginning and middle of diestrus. The dominant bacteria were Escherichia coli and Streptococcus zooepidemicus. Escherichia coli was especially dominant in maiden mares, compared to the mares that had foaled. An increase in bacterial diversity throughout the estrous cycle was observed, being highest on day 14. These results suggest that there are changes in the bacterial microbiota of the mare vagina throughout the normal estrous cycle.

Vaginal Bacteria in Mares and the Occurrence of Antimicrobial Resistance

Antibiotics are added to semen extenders in insemination doses but their effect on the vaginal microbiota of the inseminated female is unknown. The objectives of this study were to define the equine vaginal microbiota and its antimicrobial resistance, and to determine whether it changes after exposure to antibiotics in semen extenders. Vaginal swabs were taken prior to sham-insemination (day 0), and again on days 3, 7, and 14 after insemination. Isolated bacteria were identified by MALDI-TOF and tested for antimicrobial susceptibility by microdilution. The bacteria isolated from the vagina differed according to reproductive status (brood mare or maiden mare), location (north or middle of Sweden), and the stage of the estrous cycle. Five bacterial species were frequently isolated from mares in both locations: Escherichia coli, Staphylococcus capitis, Streptococcus equisimilis, Streptococcus thoraltensis, and Streptococcus zooepidemicus. Overall, vaginal bacteria isolated from inseminated mares showed higher antibiotic resistance than from non-inseminated mares, suggesting a possible link between exposure to antibiotics in the semen extender and the appearance of antimicrobial resistance. The whole-genome sequencing of E. coli isolates from inseminated mares revealed some genes which are known to confer antimicrobial resistance; however, some instances of resistance in these isolates were not characteristic of induced AMR.

Antibiotic Resistance Patterns in Cervical Microbes of Gilts and Sows

Extenders for boar semen contain antibiotics, which may induce antimicrobial resistance (AMR) in inseminated females. The objective was to investigate AMR of bacteria isolated from the cervix of sows and gilts in standing heat, representing females previously exposed to antibiotics in the semen extender and non-exposed females, respectively. Cervical swabs were taken from 30 multiparous sows and 30 gilts prior to their first insemination. After culturing on agar plates, bacterial isolates were identified by Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry and antimicrobial minimum inhibitory concentrations (MIC) were determined. Differences in antibiotic resistance between sows and gilts were analyzed by Chi-squared or Fisher's exact test. Bacteria isolated were mostly Staphylococcus spp., Streptococcus spp. and Corynebacterium spp. Higher MICs were observed for isolates from sows than from gilts. Most (>80%) Corynebacterium spp. were resistant to clindamycin; small numbers (<20%) were resistant to gentamicin, penicillin, vancomycin, ciprofloxacin and rifampicin, with no differences between gilts and sows. Corynebacterium from gilts were more often resistant to tetracycline than those from sows (25% vs. 4.17%; p = 0.04). In conclusion, bacteria from the porcine cervix showed low resistance to most antibiotics except for clindamycin, but antibacterial resistance may increase with increasing parity.

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.