The materials submitted for examination did not reveal the cause of the abortion in 67 percent of the submissions. Since this study, additional causes of bovine abortion have been discovered, such as Neospora sp. Nevertheless, the fetal, placental tissues and samples from the dam still fail to reveal a cause for abortion in the majority of diagnostic submissions. All agree that this should be less than 5 percent. Most place an expected abortion rate at about 1 to 2 percent.
Most fetal losses are unnoticed and undiagnosed.
These occurrences involve only one cow and are not investigated. They are likely some physiological disturbance not brought on by external disease agents and are of no consequence to others in the herd. Records are essential. Besides recording when pasture exposed or artificially inseminated, written histories record when pregnancy examinations were made. Records of the timing and incidence of signs of estrus are valuable in determining the reproductive history.