The aim of this study was to summarize the current status of the possible causes, clinical symptoms and pathogenesis of abortion in the mare and to evaluate the frequency of varying causes of abortion in German thoroughbred breeding. An analysis of the literature using electronic libraries, journals and textbooks was performed. In addition, the results of examinations of 123 abortions of thoroughbred breeding in central Germany were evaluated. In the literature, bacterial infections are the most frequently described cause of abortion. Other important causes are infections with equine herpesvirus (EHV)-1 or -4, twin pregnancy and umbilical cord anomalies. Examples of rare causes of abortion are equine viral arteritis (EVA), equine infectious anemia, fungal or parasitic infections, fetal malformations and diseases of the mare. In our study of 123 abortions, no cause was found in 47.2 % of the analyzed abortions. Infections were responsible for 26.8 % of the abortions. The main pathogens were bacteria in 17.1 % of the cases followed by viruses (EHV-1/4) in 8.9 % of the cases. Fungal infection was diagnosed in 0.8 % of the cases. The most common cause of a non-infectious abortion was twin pregnancy (21.1%). Other causes of non-infectious abortion were fetal malformations (3.3 %), umbilical cord strangulations (0.8 %) and uterine torsion (0.8 %). The results of our own study suggest that in the future greater attention should be paid to ultrasonographic examinations in the early pregnancy to reduce the rate of abortions because of a twin pregnancy. To increase the detection rate of unknown causes of abortion, rarer causes of abortion should be investigated, including for EVA and chlamydia, as a matter of routine.
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