The seminal microbiome/microbiota and implications for antibiotics in semen extenders.

The seminal microbiota is an integral component of fertility, both through its role in maintaining the health of the male reproductive tract and its contribution to the microbiota of the female reproductive tract. Many factors affect the dynamics of the seminal microbiota, such as the age and breed of the animal, and the husbandry conditions under which it is kept. Animal breeders introduce semen storage, representing an additional potential source of contamination. It is during this storage that the seminal microbiota can have an additional influence on sperm quality, permitting some bacteria to flourish whilst others are suppressed. Factors such as type of semen extender and temperature of storage exert an impact on the microbiota, but the predominant influence is the inclusion of antibiotics in the semen extender. Apart from a direct effect on sperm quality, these antibiotics may also alter the microbiota of the female reproductive tract, thus impacting on fertility. These factors should be borne in mind when deciding to include antibiotics in insemination doses. Alternatives to antibiotics do exist, such as physical separation of the sperm component from bacteria in the ejaculate, for example, with colloid centrifugation, and should be incorporated into prudent animal breeding strategies from a One Health perspective.