Epizootic bovine abortion
Epizootic bovine abortion has caused heavy calf losses—as high as 65% in initial pregnancies—in California beef herds since 1954. Affected cows show no signs of illness, but edema, hemorrhage, and liver damage are characteristic findings in the fetus. The cause of the disease is a large virus related to the psittacosis (parrot fever) virus. There are indications that an immunity develops in cattle which abort, but attempts to prevent the disease by vaccination have not been successful thus far. Antibiotic therapy is not a practical control measure. How the virus is maintained is not yet known. If it is proven to be venereally transmitted, artificial insemination may offer the only hope of bringing the disease under control.