Once a cow is bred, she should calve about 283 days later. However, sometimes the pregnancy is lost.
Late pregnancy loss is usually visible; you find the aborted fetus or the cow with placental membranes hanging from the vulva. “But with early pregnancy loss, you don’t have a clue,” says Ahmed Tibary, DVM and Washington State University (WSU) professor of theriogenology.
Tibary says pregnancy loss should be considered a possibility whenever there’s a longer-than-average calving season, or higher-than-usual number of late-calving cows. Cows that settled late may have bred early but lost their pregnancies and rebred on a later cycle.
Ram Kasimanickam, a DVM in WSU’s Department of Veterinary Clinical Sciences, says there are three categories of pregnancy loss – early embryonic death, abortion and stillbirth.
The conceptus is an embryo during the first 42 days; after that, all major organs and body systems have formed and it becomes a fetus. If loss occurs before 42 days, it’s termed early embryonic death. After that, it is considered an abortion.
“Abortion involves expulsion of a dead fetus, or a living one incapable of maintaining life outside the uterus. Stillbirth is a full-term calf that’s dead at birth,” Kasimanickam explains.
Many things can terminate pregnancy. “Most of the time we suspect infectious causes like trichomoniasis or campylobacteriosis (vibrio), but there may be non-infectious causes,” Tibary says. These could include genetic abnormalities, malnutrition, stress or poisons.