Essential oils and swine reproduction: new frontiers in antibiotic replacement in seminal doses

The actual scenario regarding antibiotic resistance is extremely worrying and the scientific community invest time and efforts in the search for solutions. Essential oils (EOs) are products of the secondary metabolism of aromatic plants and are complex mixtures of several compounds. EOs show a wide variety of biological activities, that may suggest interesting applications in the reproduction field, as cryo-preservatives or substitutes for antibiotics, but studies regarding their effects on spermatozoa are lacking. The present research aimed at evaluating the opportunity to use essential oils in refrigerated swine seminal doses as a potential alternative to antibiotics. The preliminary step was about the study of swine seminal parameters in farm setting using advanced statistical methods, to better predict in vivo fertility on the basis of semen morpho-functional evaluations. In the first step some specific EOs were selected and the cytotoxic effects on swine spermatozoa were evaluated to identify non-spermicidal concentrations. The lower concentrations of Rosmarinus officinalis and Melaleuca alternifolia EOs not impacted the semen morpho-functinal parameters. The last step was the evaluation of antibacterial effects of the previously tested concentrations on the liquid phase of swine refrigerated seminal doses. In order to obtain standardized results, an in vitro model with the addition of E. coli was set up. Analyses, performed at 24 and 120 hours, included optical density evaluation, bacterial DNA quantification by qPCR, and colony count. The results demonstrated that both EOs, at a concentration of 0.4 mg/ml, are capable of delivering similar effects to ampicillin. At the lower concentration, M. alternifolia EO seemed more effective when compared to R. officinalis. In conclusion, this project showed the potential of some EOs in the field of swine artificial insemination, but also highlighted how it is necessary, before claiming natural compounds as future “miracle-workers”, to investigate their safety and mechanisms of action.