Abortions usually occur in the last trimester, although first and second trimester abortions are also seen. The state of preservation of the fetus is variable. The placenta is often retained and may be heavily contaminated. Grossly, it appears autolytic and has a yellow to brown exudate over swollen and edematous cotyledons. As described in this case, fetuses may have a characteristic hemorrhagic cast in the trachea.
Lungs are dark red, swollen, and have minute yellow foci on the pleural surface.
Histologically, there may be numerous bacteria with no inflammatory cells or a suppurative reaction may be present. Fungal hyphae with morphologic characteristics of a mucoraceous zygomycete are present within the placenta, occasionally within the walls of blood vessels. Both the bacterial and fungal infections probably contributed to the abortion. North Dakota Veterinary Diagnostic Laboratory, NDSU, Van Es Hall, Fargo, ND 58105-5406. Abortion caused by Actinomyces pyogenes in laboratory diagnosis of livestock abortion.