Yes, animals have miscarriages. Pregnancy loss occurs across virtually every animal group, from mammals and birds to reptiles, and it is surprisingly common. In dairy cows, about 10% of confirmed pregnancies end in loss before 90 days. In chimpanzees, roughly 16% of clinically recognized pregnancies fail. These numbers mirror the approximately 15% rate seen in recognized human pregnancies, suggesting that pregnancy loss is a deeply rooted biological reality rather than something unique to people.
How Animal Miscarriage Differs From Human Miscarriage
Veterinary medicine uses the term “spontaneous abortion” rather than miscarriage, though the meaning is the same: the loss of a pregnancy without any deliberate interference. In livestock like cattle and horses, the process often looks similar to what happens in humans, with the body expelling the fetus and associated tissue.
In smaller mammals like rodents, though, something different happens. Instead of expelling a failed pregnancy, the mother’s body reabsorbs it. This process, called fetal resorption, unfolds in stages: first the embryo stops growing normally, then its heartbeat slows and fluid builds up around the heart, then development stops entirely. Over the course of one to two days, the embryo and its surrounding cavity disappear as maternal immune cells break down and absorb the tissue. From the outside, there may be no visible sign that the animal was ever pregnant. This is one reason pregnancy loss in small animals and wildlife often goes unnoticed.
How Common Pregnancy Loss Is in Different Species
The timing of pregnancy matters enormously. A large meta-analysis covering nearly 20,000 dairy cow pregnancies found that losses averaged 27% in the earliest embryonic stage (around days 19 to 32), dropped to 13% in the late embryonic stage, fell to 7% in the early fetal period, and reached just 2% by the later fetal stage (days 60 to 90). The pattern is clear: the earlier the pregnancy, the higher the risk of loss. This mirrors the human pattern almost exactly.
Chimpanzees show a strikingly similar picture. Research from a captive colony found that about 16% of clinically recognized chimpanzee pregnancies ended in loss. In humans, about 70% of all conceptions fail to reach viability when you include losses so early the woman never knew she was pregnant. Between 22% and 50% of human pregnancies are lost before the first missed menstrual period. That enormous rate of invisible early loss likely occurs in other primates and mammals too, but it is nearly impossible to measure in animals that can’t report their own symptoms.
In birds, the process looks different but the outcome is similar. Studies on geese found embryonic mortality rates ranging from about 5% to 9% of fertile eggs across different breeding lines, with chromosomal abnormalities present in 8% to 15% of the embryos that died.
Genetic Problems Are a Leading Cause
Just as in humans, where chromosomal abnormalities cause the majority of early miscarriages, genetic defects play a major role in animal pregnancy loss. In the goose studies, researchers found that the father’s genetics significantly influenced embryonic death rates, and certain family lines consistently produced higher rates of loss. When researchers specifically selected for animals with higher embryonic mortality, the rate of chromosomal abnormalities among dead embryos jumped to between 12% and 35%.
Interestingly, the specific chromosomal errors didn’t repeat from one breeding season to the next, meaning each pregnancy produced its own random genetic mistakes. But the overall tendency toward pregnancy loss did repeat, with a repeatability coefficient of 0.54, suggesting that some animals are simply more prone to producing embryos with fatal defects.
Infections That Trigger Mass Pregnancy Loss
Infectious disease is one of the most devastating causes of animal miscarriage, particularly in livestock. Seven major disease groups are known to cause widespread pregnancy loss in domestic animals: brucellosis, leptospirosis, Q fever, listeriosis, chlamydia-related infections, toxoplasmosis, and campylobacteriosis. All of these can also infect humans, which is one reason veterinary authorities monitor them closely.
Brucellosis, for instance, can sweep through a cattle herd and cause nearly every pregnant animal to abort. Toxoplasmosis, carried by cats and spread through their feces, is a well-known cause of pregnancy loss in sheep and goats. These infections don’t just affect individual animals. A single outbreak can cause dozens or hundreds of miscarriages in a herd or flock within weeks, making infectious abortion one of the most economically significant problems in agriculture.
Environmental and Chemical Threats
Chemical exposures cause pregnancy loss in both wild and domestic animals. Endocrine disruptors, heavy metals, solvents, pesticides, plastics, and industrial chemicals have all been linked to reproductive failure in laboratory animals and wildlife. These substances can interfere with hormones critical for maintaining pregnancy, leading to subfertility, fetal growth problems, death in the womb, and birth defects. Dioxins are among the most well-documented reproductive toxicants. For livestock, certain poisonous plants in grazing pastures are a common and preventable cause of pregnancy loss.
When Males Cause Pregnancy Loss
One of the most unusual forms of animal miscarriage has no equivalent in humans. In rodents, a phenomenon called the Bruce effect causes females to terminate their own pregnancies when exposed to a male that is not the father. The mechanism is hormonal: exposure to the unfamiliar male shifts the balance between estrogen and progesterone, disrupting the uterine environment so the embryo can no longer implant or survive. No aggression from the male is required. His scent alone is enough to trigger the process.
From an evolutionary perspective, this may be adaptive. If a new dominant male has taken over a territory and would likely kill existing offspring (as happens in many rodent and primate species), terminating the pregnancy early saves the mother’s energy for a future litter fathered by the new male. The Bruce effect has been documented most clearly in mice, but evidence suggests similar mechanisms may operate in other species.
Signs of Miscarriage in Dogs and Cats
For pet owners with a pregnant dog or cat, the signs of miscarriage can be subtle or dramatic depending on how far along the pregnancy is. Early losses, especially those involving resorption, may produce no visible symptoms at all. The owner may simply notice that the animal’s belly stops growing or that the expected litter never arrives.
Later in pregnancy, more obvious signs appear: bloody or pus-like discharge from the vulva, a noticeable decrease in belly size, vomiting, diarrhea, poor appetite, lethargy, fever, abdominal straining, and visible discomfort. One telling sign is when a dog or cat begins lactating or showing nesting behavior at the expected delivery date but never actually gives birth. This can indicate that the pregnancy was lost and the body reabsorbed the fetuses while still progressing through some of the hormonal stages of late pregnancy.
How Veterinarians Confirm Pregnancy Loss
Ultrasound is the primary tool for diagnosing miscarriage in animals, considered the gold standard with accuracy approaching 100% when performed by an experienced technician. Veterinarians look for specific signs: the absence of a heartbeat, separation of the placenta from the uterine wall, or reduced fluid volume around the embryo. In cattle, losses between days 24 and 40 of gestation are diagnosed this way.
Blood tests offer another approach. In cows, a protein produced by the placenta circulates in the mother’s blood, and low levels around day 28 to 31 of gestation can predict pregnancy loss with about 95% accuracy. Researchers have also identified tiny molecules called microRNAs that appear in higher amounts in cows destined to lose their pregnancies, detectable as early as day 17 of gestation. These tools are primarily used in agriculture, where the economic stakes of pregnancy loss are high and early detection allows farmers to re-breed animals sooner.