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Important viral, bacterial and parasitic agents of the equine reproductive tract and their diagnostic detection Viral, bacterial and parasitic diseases of the equine reproduction tract are a common cause of infertility, abortions and premature births and are responsible for economic losses in horse populations. Both viral agents like equine herpesvirus type 1 and equine arteritisvirus and bacterial agents like Streptococcus equi subsp. zooepidemicus, Actinobacillus equuli, leptospira, chlamydia and Taylorella equigenitalis are important infectious agents for the breeding and export of horses. Horses to be exported must be examined for the parasites Babesis caballi, Theileria equi, the causative agent of the tick-borne protozoal disease, equine piroplasmosis, and for Trypanosoma equiperdum, the causative agent of dourine. Identification and differentiation of the pathogen and the existing condition require both intensive clinical examination and a comprehensive laboratory diagnostic analysis. Depending on the diagnostic purpose, it is possible to differentiate between indirect and direct detection of the agents. Indirect methods facilitate the detection of antibodies against infectious agents and give further information about the immune status of the horse. Depending on the testing method and the animal's vaccination status, conclusions can be drawn about the infection and the success of vaccination. Direct test methods make possible the identification and differentiation of the agent isolated in the diagnostic sample. In horses with genital infections, infertility and abortions, diagnosis of viral infections is based on isolation of the virus in cell culture or on the detection of specific DNA by polymerase chain reaction techniques. Culture and biochemical identification remain the gold standard for confirming the presence of bacterial pathogens. The polymerase chain reaction offers an alternative or supplement to culture identification and provides highly specific and sensitive results that can often be obtained more quickly than by culture. A serological response to viral, bacterial and parasitic infections can be demonstrated by serological testing of paired sera to show a rise in antibody titre.Depending on the epidemiology of the pathogen and the site of the disease, important factors for a reliable diagnosis are the diagnostic material and the time and technique of sampling.