**5. Conclusions**

In conclusion, this study demonstrated, for the first time, changes in salivary oxytocin concentration in breeding boars during ejaculate collection time. However, the magnitude and significance of changes are di fferent depending on the assay used for its measurement, with the polyclonal assay better suited for detecting changes in oxytocin concentrations than the monoclonal assay. In addition, increases in salivary oxytocin concentrations at ejaculation time in younger boars, in boars showing greater libido intensity, and those of the Pietrain breed, were observed. Overall, this study opens a new line of research about the possible use of salivary oxytocin concentration as potential biomarker of sexual behavior of breeding male pigs. In this context, it would also be interesting to evaluate whether the salivary levels of oxytocin are related to the quantity and quality of semen. This study also suggests the potential use of salivary levels of oxytocin for evaluating the welfare of boars, and for detecting or monitoring problems associated with a low reproductive performance.

**Author Contributions:** Conceptualization, J.J.C. and J.R.; methodology, M.L.-A. and L.P.; validation, M.L.-A. and S.M.-S.; formal analysis, M.L.-A., J.J.C. and S.M.-S; investigation, M.L.-A., L.P. and S.M.-S; writing—original draft preparation, M.L.-A., J.J.C. and S.M.-S; writing—review and editing, L.P. and J.R.; supervision, J.R., J.J.C. and S.M.-S; funding acquisition, J.J.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by 'MINECO (Spain), FEDER funds (EU)' (AGL2016−79096-R) and MECD (Spain) FPU16/02170. M.L.-A. was financially supported by 'MECD-FPU' (Madrid, Spain) FPU16/02170.

**Acknowledgments:** The authors wish to thank the farm workers for their participation in this research.

**Conflicts of Interest:** The authors declare no conflict of interest.
