Relevance of Leptospira in boar and for the development of alternative antimicrobial concepts in boar semen preservation

Leptospirosis is a zoonotic disease of importance to public health and in livestock productions. It causes significant economic losses in pig breeding farms worldwide. However, actual transmission cycles and disease epidemiology in the pig population remain largely unknown. Despite the fact that the potential risk of venereal transmission of pathogenic Leptospira serovars in pigs has been a topic of discussion since the 1970s, reliable data are still lacking compared to other livestock species. Consequently, antibiotics are added to semen extenders to reduce bacterial contamination including pathogens like Leptospira. In view of the global threat of antimicrobial resistances, the routine use of antibiotics in porcine semen extenders is now under debate. Information about the prevalence of Leptospira infections in boar used for artificial insemination is needed for the development of novel antimicrobial concepts in pig insemination. This short report provides a summary of the state of knowledge, together with negative results from real-time PCR analyses for the detection of pathogenic Leptospira DNA in boar semen. Molecular analyses were performed on 96 raw and extended samples obtained from normospermic ejaculates of 58 boar housed in six different studs in Germany. In the absence of reliable data, it is important to raise the awareness for a subject that can represent a challenge for pig productions in keeping reproductive health and food safety at high levels. The present molecular results indicate that Leptospira might not be a common threat in boar semen. Conclusive evidence would require results from a systematic serological surveillance of boar, combined with seasonal molecular analyses of semen to identify potential carriers, and assess actual seroprevalences, associated Leptospira serovars and transmission events.