Antibiotics may be added to semen extenders when preparing commercial semen doses for artificial insemination according to national and international guidelines, but this practice could represent a non-therapeutic usage and contribute to the development of antibiotic resistance, according to a recent post in the Swedish University of Agricultural Sciences (SLU) Knowledge Bank.

A study reported by J.M. Morrell et al. in the journal Theriogenology showed that colloid centrifugation reduced 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, SLU noted.

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, the researchers said.

According to the post, ejaculates from nine boars were extended in Beltsville Thawing Solution without antibiotics and were transported to the laboratory for single layer centrifugation 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 control and M samples and five of the S samples did not contain any bacteria, the researchers said. Mean bacterial counts for the remaining samples (colony forming units [CFU] per milliliter) were as follows: control, 259 + 216 CFU/mL; S, 30 + 22 CFU/mL, and M, 33 + 15 CFU/mL (P < 0.01).

Citrobacter spp., Staphylococcus simulans, Klebsiella variicola, Escherichia coli, Myroides odoratimimus, Proteus spp. and Enterococcus faecalis were identified in the control samples, they noted.

According to the researchers, there were marginal differences in sperm quality among treatments, with sperm velocity and linearity being higher in S and M samples than in control samples at all time points. However, sperm viability, capacitation and acrosome status on day 0 were marginally better in controls than in S or M, but these differences disappeared during storage, the researchers added.

Morrell et al. concluded that 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, the researchers added.