A mare can carry a dead foal for days to several weeks, depending on when in gestation the foal dies, whether the cervix stays closed, and how quickly the mare’s body responds. In most cases, the mare will eventually go into labor and expel the fetus on her own, but the longer a dead foal remains inside, the greater the risk of life-threatening infection, toxic shock, and a painful hoof condition called laminitis. Prompt veterinary involvement is critical once fetal death is suspected.
What Determines How Long Retention Lasts
The timeline depends largely on the stage of pregnancy and the condition of the cervix. In late gestation, when a foal dies close to its expected due date, many mares will begin labor within a few days. Hormonal signals that normally trigger foaling are disrupted, though, so it’s not unusual for the process to stall. Some mares show no outward signs of distress for a week or more, carrying the dead foal without obvious changes in behavior.
Earlier in pregnancy, the timeline stretches considerably. If the fetus dies after its bones have fully formed but well before term, the mare’s body may take weeks to recognize the loss and initiate expulsion. In rare cases, the dead fetus is retained for months. What happens next inside the uterus depends almost entirely on one factor: whether bacteria can reach the fetus.
Mummification vs. Maceration
When a foal dies in utero and the cervix remains tightly closed, two very different processes can unfold.
Mummification occurs when the uterus stays sealed, keeping out both oxygen and bacteria. Fetal and uterine fluids are gradually reabsorbed, and normal decomposition stalls. The tissue dries out below a critical water threshold where bacteria simply can’t survive. Over several weeks, the fetus shrivels into a dry, leathery mass of skin, tendons, and bones. For mummification to happen, the fetus must have died after its skeleton was well developed. If death occurs earlier, the soft tissues break down and are absorbed through the uterine lining before mummification can take hold. A mummified fetus can remain inside the mare for weeks to months, sometimes discovered only when a veterinarian investigates why the mare isn’t cycling or conceiving.
Maceration is the opposite scenario. If the cervix opens even slightly, bacteria and oxygen enter the uterus, and the dead fetus begins to putrefy. This is a far more dangerous situation. Bacterial toxins can cross into the mare’s bloodstream, causing severe uterine infection (metritis), systemic toxemia, and laminitis. Maceration demands urgent veterinary treatment because the mare’s condition can deteriorate rapidly, sometimes within 24 to 48 hours of the first signs of illness.
Warning Signs in the Mare
A mare carrying a dead foal doesn’t always look sick right away. Early clues can be subtle: a loss of udder development that had been progressing, a change in appetite, or mild colic-like discomfort. As the situation advances, more obvious signs appear. Foul-smelling vaginal discharge is a strong indicator that maceration or infection has set in. Fever, depression, reluctance to move, and shifting weight off the front feet (a hallmark of laminitis) all signal that the mare needs immediate help.
In cases of mummification, external signs may be minimal. The mare might simply fail to foal at her expected date, or she may appear to go out of heat and stop showing normal cycling behavior. Some owners don’t realize anything is wrong until the mare is examined for a new breeding season.
How a Veterinarian Removes a Dead Foal
Once fetal death is confirmed, most veterinarians move quickly to induce expulsion rather than waiting for the mare’s body to act on its own. The standard approach uses hormones that stimulate uterine contractions. Mares commonly experience transient side effects within about 20 minutes of treatment, including heavy sweating, mild colic, and restlessness. If the initial treatment doesn’t produce results within a couple of days, additional hormones may be given alongside techniques to soften and dilate the cervix.
In some cases, the veterinarian will manually assist delivery or use instruments to break down retained membranes. If the fetus has mummified and is firmly adhered, manual extraction under sedation may be necessary. Uterine flushing with antiseptic solutions helps clear debris and reduce infection risk after the fetus is removed.
Risks of Delayed Removal
The biggest dangers of prolonged retention are infection, endotoxemia (bacterial toxins flooding the bloodstream), and laminitis. These three complications often occur together and can escalate quickly. Laminitis in particular can cause permanent structural damage to the hooves, and the long-term prognosis for mares that develop severe laminitis alongside toxic shock and uterine infection is poor to moderate. In the worst cases, the combination is fatal.
Even without obvious infection, a retained dead fetus alters the uterine environment in ways that can complicate recovery. The longer the tissues remain, the more inflammation builds, and the harder it becomes for the uterus to heal cleanly.
Future Fertility After Fetal Loss
The good news is that mares who recover from fetal retention, including retained membranes, do not generally have lower fertility afterward. The uterus has a strong capacity to heal once the source of the problem is removed and any infection is treated. Many mares go on to conceive and carry healthy foals in subsequent breeding seasons.
The key variable is how much damage occurred before treatment. A mare whose dead foal was identified and removed promptly, with no significant infection, has an excellent reproductive outlook. A mare who developed severe metritis or laminitis faces a longer recovery and may need additional veterinary screening before being bred again. Veterinarians often recommend submitting the expelled fetus and placenta to a laboratory to identify the underlying cause of death, which helps guide management decisions for future pregnancies and can reveal whether the loss was a one-time event or something likely to recur.