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

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.

Application of Flow Cytometry Using Advanced Chromatin Analyses for Assessing Changes in Sperm Structure and DNA Integrity in a Porcine Model

Chromatin status is critical for sperm fertility and reflects spermatogenic success. We tested a multivariate approach for studying pig sperm chromatin structure to capture its complexity with a set of quick and simple techniques, going beyond the usual assessment of DNA damage. Sperm doses from 36 boars (3 ejaculates/boar) were stored at 17 °C and analyzed on days 0 and 11. Analyses were: CASA (motility) and flow cytometry to assess sperm functionality and chromatin structure by SCSA (%DFI, DNA fragmentation; %HDS, chromatin maturity), monobromobimane (mBBr, tiol status/disulfide bridges between protamines), chromomycin A3 (CMA3, protamination), and 8-hydroxy-2'-deoxyguanosine (8-oxo-dG, DNA oxidative damage). Data were analyzed using linear models for the effects of boar and storage, correlations, and multivariate analysis as hierarchical clustering and principal component analysis (PCA). Storage reduced sperm quality parameters, mainly motility, with no critical oxidative stress increases, while chromatin status worsened slightly (%DFI and 8-oxo-dG increased while mBBr MFI-median fluorescence intensity-and disulfide bridge levels decreased). Boar significantly affected most chromatin variables except CMA3; storage also affected most variables except %HDS. At day 0, sperm chromatin variables clustered closely, except for CMA3, and %HDS and 8-oxo-dG correlated with many variables (notably, mBBr). After storage, the relation between %HDS and 8-oxo-dG remained, but correlations among other variables disappeared, and mBBr variables clustered separately. The PCA suggested a considerable influence of mBBr on sample variance, especially regarding storage, with SCSA and 8-oxo-dG affecting between-sample variability. Overall, CMA3 was the least informative, in contrast with results in other species. The combination of DNA fragmentation, DNA oxidation, chromatin compaction, and tiol status seems a good candidate for obtaining a complete picture of pig sperm nucleus status. It raises many questions for future molecular studies and deserves further research to establish its usefulness as a fertility predictor in multivariate models. The usefulness of CMA3 should be clarified.