Pregnancy Loss

Pregnancy loss in mares represents one of the most emotionally difficult situations any breeder faces, combining the disappointment of lost breeding season with the genuine concern about the mare's health and future reproductive potential. Whether it occurs early in pregnancy as a spontaneous abortion or later as a stillbirth, losing a foal strikes at the heart of why people breed horses in the first place. Understanding what causes pregnancy loss, recognizing the early signs that something might be going wrong, and knowing how to support a mare through this experience becomes essential knowledge for anyone managing breeding stock.

Pregnancy loss happens more frequently than many people realize, though the exact frequency varies depending on the mare's age, health status, and management practices. Younger mares in their prime breeding years generally have better reproductive success, while very young mares still developing their own bodies and older mares past their peak fertility years experience higher loss rates. But even healthy mares in ideal conditions can lose pregnancies for reasons that have nothing to do with owner negligence or poor care. The randomness of some pregnancy losses can be particularly difficult emotionally, leaving breeders wondering what they could have done differently when often the answer is simply that sometimes nature doesn't cooperate.

Pregnancy loss encompasses several different situations that require different management approaches. Early pregnancy loss, occurring before day 90, often goes unnoticed because many breeders don't even know their mare was pregnant yet. Mid-pregnancy loss, typically occurring between day 90 and month seven, becomes more obvious as the mare's appearance changes and her behavior shifts. Late-term pregnancy loss or stillbirth can occur in the final months or even during labor itself. Each scenario presents different challenges for understanding what happened and preventing similar losses in future pregnancies.

The impact of pregnancy loss extends beyond the immediate emotional disappointment. A mare that loses a pregnancy still had to be managed during those months, with breeding plans disrupted and the entire breeding season potentially compromised. If the loss occurs late in pregnancy, the mare may need veterinary care to safely expel the pregnancy and ensure her own health isn't endangered. Understanding what normal recovery looks like and when to be concerned about complications helps ensure the mare returns to good health and can be successfully bred again.

This guide walks you through the complex landscape of equine pregnancy loss, exploring what causes it, how to recognize early warning signs, what happens during veterinary diagnosis, and most importantly, how to support your mare through this experience and protect her future reproductive potential. While pregnancy loss can feel like failure, it's often simply biology doing what it does sometimes. With knowledge and appropriate care, most mares recover fully and go on to carry successful pregnancies.

The causes of pregnancy loss in mares are surprisingly diverse, ranging from infectious disease to purely genetic factors to circumstances entirely outside anyone's control. Infection represents one of the most common preventable causes of pregnancy loss, with specific organisms like Equine Herpesvirus-1 and Equine Arteritis Virus notorious for causing abortion in pregnant mares. These viral infections can cause the mare's immune system to reject the pregnancy, or they can directly damage the developing foal. Bacterial infections ascending from the lower reproductive tract can also cause pregnancy loss, particularly if the mare's cervical seal isn't adequate to prevent contamination of the uterus during pregnancy.

Genetic factors play a significant role in many pregnancy losses, though most of these are invisible to us until the pregnancy fails. Chromosomal abnormalities in the developing foal lead the mare's body to naturally abort rather than continue carrying a foal with incompatible-with-life defects. This is actually a healthy response, preventing the birth of a severely compromised foal. Some of these genetic losses are random developmental mistakes with no connection to the mare's or stallion's genetics. Others reflect genetic incompatibilities between the specific pair of horses, which might mean trying a different breeding combination could succeed.

Hormonal insufficiency causes pregnancy loss when the mare's body doesn't produce adequate progesterone to maintain the uterine environment the pregnancy needs. The corpus luteum, the ovarian structure that produces progesterone after ovulation, sometimes fails to maintain adequate hormone levels throughout pregnancy. Early in pregnancy, the embryo's own hormonal signals gradually take over maintaining the pregnancy, but if this transition fails to occur properly, pregnancy loss can result. Some mares seem more prone to hormonal issues than others, and these mares may benefit from progesterone supplementation during future pregnancies to prevent recurrent loss.

Environmental and management factors significantly influence pregnancy loss rates. Excessive stress, whether from transport, dramatic environmental changes, or psychological stress, can trigger pregnancy loss through hormonal disruption. Nutritional deficiencies leave the mare's body unable to adequately support the pregnancy, particularly if she's in poor body condition or receiving inadequate mineral balance. Poor quality hay or grain, extreme weather exposure, or lack of shelter during late pregnancy all contribute to losses. Trauma from falls, being kicked by other horses, or collisions in the field can cause pregnancy loss if the impact damages the uterus or causes sufficient stress to the mare's system.

Pregnancy loss also occurs as a consequence of other health problems the mare already has. Severe colic episodes can trigger loss. Systemic infections like pneumonia or septicemia damage the mare's overall health so significantly that the pregnancy cannot be sustained. Joint or bone infections that cause fever and systemic inflammation compromise pregnancy stability. Some mares have anatomical issues that predispose them to pregnancy loss, such as poor cervical function that allows bacterial contamination or uterine scarring from previous infections that compromises the pregnancy site. These mares may have better success with careful management and veterinary support during future pregnancies.

Age represents a significant risk factor for pregnancy loss in both very young and older mares. Young mares still developing their own bodies lack the physical resources to reliably support a pregnancy while still growing. Mares in their twenties and beyond have declining reproductive efficiency, and pregnancy loss rates increase noticeably. Maiden mares carrying their first pregnancy lose pregnancies more frequently than experienced broodmares, though most maiden mares go on to successfully carry future pregnancies. The exact mechanisms aren't entirely understood, but age-related changes in egg quality and uterine function almost certainly play roles.

Early pregnancy loss often goes undetected because most breeders don't know their mare was pregnant. A mare that was in foal but loses the pregnancy before six weeks might simply fail to conceive again if you're not specifically looking for pregnancy confirmation. Some owners notice a brief period of discharge or slight behavioral changes, but these signs are subtle and easily missed. By the time pregnancy is confirmed via ultrasound, some mares have already lost the pregnancy you didn't know existed, and they'll appear to have simply failed to conceive.

As pregnancy progresses beyond the early weeks, physical changes become more obvious. The pregnant mare's body gradually becomes rounder, particularly in the lower abdomen as the foal grows. Her udder may begin enlarging as pregnancy advances, though this varies among mares. Some mares show behavioral changes, becoming calmer and more nurturing in their demeanor. Increased appetite is common in pregnant mares, and they often seem focused on eating and resting more than usual.

If pregnancy loss is going to occur, the mare's behavior often changes noticeably before physical signs become obvious. She may suddenly become anxious, restless, or irritable. Some mares stop eating normally or drink excessively. Her attitude may shift from calm and content to agitated or withdrawn. These behavioral changes reflect the mare's body recognizing that something is going wrong with the pregnancy, even before visual or physical signs develop. Paying attention to subtle changes in how your mare acts can provide early warning that something needs veterinary attention.

As loss approaches, discharge becomes one of the most obvious signs. Vaginal discharge can range from clear to bloody to a darker blood-tinged fluid. The amount varies, but any unusual discharge during pregnancy warrants prompt veterinary evaluation. Some mares develop visible swelling of the vulva or signs of discomfort when urinating or defecating. Others show signs similar to early labor without actually being close to a normal due date, including restlessness, sweating, or visible contractions.

The progression of loss varies dramatically depending on its cause and timing. Some mares seem to lose pregnancies quietly, with minimal discharge or discomfort, and the owner only realizes something happened when the mare comes back into heat or at the next ultrasound. Other mares experience severe colic-like signs, sweating, and apparent pain as they pass the pregnancy. The mare's overall health status during loss ranges from completely normal behavior and appetite to severe depression and potential shock if significant hemorrhage occurs. Late-term losses, particularly if accompanied by placental retention or infection, can create serious health emergencies.

After pregnancy loss, mares often show signs of emotional distress alongside the physical recovery. Some mares become agitated or anxious, calling out and searching, seemingly aware that something is missing from their life. Others become withdrawn and depressed, with reduced appetite and less interest in their surroundings. These behavioral changes are temporary in most cases but reflect the mare's significant physiological and possibly emotional investment in the pregnancy that was lost. Understanding that these behavioral responses are normal helps prevent overreaction during the recovery period.

When pregnancy loss is suspected, veterinary evaluation becomes essential to understand what happened and to ensure the mare's own health and safety. The veterinarian will take a detailed history about the mare's management, recent health issues, breeding history, and any signs you've observed. Physical examination includes checking the mare's vital signs for fever or signs of shock, evaluating her hydration status, and performing a palpation of the abdomen to assess for pain or other problems. The vulva and vagina are examined for discharge or tissue damage, and the cervix is evaluated to determine if it's open or closed.

Ultrasound examination provides crucial information about what's happening in the uterus. In early pregnancy loss, the ultrasound may show an empty uterus, confirming the pregnancy is gone. If the mare is actively losing the pregnancy, ultrasound might reveal retained fetal tissue or placental material that needs to be evacuated. The uterus is assessed for signs of infection or inflammation. Blood work helps determine if the mare has an active infection, providing information that guides antibiotic treatment if needed. In some cases, cultures of uterine or cervical fluids help identify specific infections responsible for the loss.

Specific diagnostic tests depend on the timing and presentation of loss. If tissue is available, it can sometimes be submitted for genetic analysis to determine if chromosomal abnormalities caused the loss. This information is valuable for mares with recurrent losses, as it helps determine whether changing breeding partners might improve success. Hormone testing can evaluate whether progesterone insufficiency contributed to the loss, providing guidance for supplementation in future pregnancies. Infectious disease testing, particularly for horses in regions where certain viruses are prevalent, can identify specific infections that caused loss and guide biosecurity and vaccination decisions.

Treatment during active pregnancy loss focuses on supporting the mare's health and safety through the process. If the mare is actively expelling fetal tissue, the veterinarian typically allows the process to continue naturally unless complications arise. Oxytocin might be administered to stimulate contractions if they're weak or ineffective, helping ensure complete evacuation of the pregnancy. If the mare is in severe pain, pain medication provides comfort while allowing her body to complete the process naturally. Intravenous fluids may be necessary if the mare is dehydrated or in shock from significant hemorrhage.

If retained fetal membranes result from the loss, manual removal by a veterinarian becomes necessary to prevent serious infection. Retained placental material can lead to metritis, a life-threatening uterine infection that requires aggressive treatment. Once membranes are removed, thorough uterine lavage, or flushing of the uterus with sterile fluid, helps remove any remaining tissue or contamination. Antibiotics are administered based on culture results or broad spectrum coverage if infection is likely. The mare is monitored closely in the days following loss to watch for signs of infection or other complications.

Recovery from pregnancy loss typically takes several weeks, with the mare's hormonal system gradually returning to a non-pregnant state. Heat cycles usually resume within days to a few weeks of loss, depending on how far along the pregnancy was. Before attempting to breed again, most veterinarians recommend allowing at least one normal cycle and possibly performing a uterine biopsy to ensure the lining is healthy and free of infection. Mares with recurrent losses benefit from progesterone supplementation during future pregnancies, starting immediately after ovulation and continuing through at least the first 120 days of pregnancy. This provides extra support during the critical early weeks when progesterone insufficiency is most likely to cause loss.

Supporting a mare through pregnancy loss requires both physical care and emotional understanding. During active loss, the mare needs a safe, clean space where she can move around comfortably without risk of injury or contamination. A stall with good footing, clean bedding, and access to water helps her manage the physical process safely. If she's distressed, being turned out in a quiet pasture away from other horses may help her feel calmer, though she shouldn't be left alone if possible complications might arise. Monitoring her closely while respecting her need for privacy represents the balance during this time.

Feeding during loss should follow the mare's appetite and the veterinarian's recommendations. Most mares continue eating normally through pregnancy loss, though some have reduced appetite temporarily. Offering quality hay and her regular grain ration maintains her strength during recovery. If she has digestive upset or colic-like signs, temporarily reducing grain and offering only hay may be appropriate. Once acute loss is complete, resuming normal nutrition becomes important to support recovery and prepare for future breeding.

Exercise during loss should be minimal, with the mare confined to a stall or small paddock to prevent injury or excessive exertion. After the acute phase passes and the mare seems comfortable, gradually increasing activity promotes circulation and psychological wellbeing. However, strenuous exercise or long rides should be avoided during the recovery period. Most mares return to normal activity within a few weeks of loss, though individual mares vary.

Medication management during recovery depends on what the veterinarian recommended. If antibiotics were prescribed, completing the entire course is essential even if the mare seems completely recovered. If progesterone supplementation was discussed for future pregnancies, discussing timing for implementation with your veterinarian ensures you're prepared for the next breeding season. Pain medication should be given as directed if the mare shows discomfort during recovery, though most mares recover without significant pain once acute loss is complete.

Handling the emotional aspects of loss affects how you manage the mare during recovery. A mare that shows distress and calling can sometimes be helped by removing her from proximity to other mares, or alternatively, some mares settle better with a calm companion. Excessive handling or emotional intensity from the owner can add to the mare's stress during an already difficult time. Treating her calmly and normally while being attentive to her needs strikes the right balance. The mare will recover physically, and her hormonal state will normalize even if her behavior temporarily reflects the loss.

Planning for future pregnancies requires conversation with your veterinarian about whether management changes or preventive interventions would improve success. If the loss was attributed to infection, biosecurity measures become important. If nutritional deficiency contributed, adjusting feeding programs prevents recurrence. If progesterone insufficiency was the cause, planning for supplementation during future pregnancies offers real hope for success. Most mares that experience one pregnancy loss go on to successfully carry the next pregnancy, particularly with appropriate support and intervention.

Preventing pregnancy loss starts with recognizing the significant factors within your control and accepting that some losses happen regardless of perfect management. Maintaining the mare in excellent health before breeding significantly reduces loss risk. A mare in good body condition, properly vaccinated against infectious diseases known to cause abortion, and receiving excellent nutrition has the best possible odds of carrying a successful pregnancy. Establishing a relationship with an equine reproduction specialist allows discussion of any concerns about a specific mare's breeding history and planning of appropriate interventions.

Vaccination against Equine Herpesvirus-1 and Equine Arteritis Virus protects mares against two significant infectious causes of pregnancy loss. Vaccination protocols should follow current recommendations, which sometimes include specific revaccination during pregnancy to provide additional protection. If your region has known infection risk, your veterinarian may recommend additional biosecurity measures to prevent exposure. These preventive steps can eliminate one category of loss risk entirely.

Nutritional management before and during pregnancy influences loss risk. Mares should be in adequate body condition at breeding, not overweight but not thin either. Feeding a balanced diet with appropriate mineral ratios, particularly calcium and phosphorus balance, supports both mare health and healthy foal development. Providing quality feed and clean water at all times maintains nutritional status. Some mares benefit from specific supplements, which your veterinarian can recommend based on your hay and grain analysis.

Stress reduction during pregnancy helps maintain hormonal stability that supports the pregnancy. Avoiding unnecessary transport during the first trimester, when loss risk is highest, prevents stress during the critical period. Maintaining consistent management routines, avoiding dramatic environmental changes, and protecting the mare from injury or trauma reduces stress-related loss risk. While you can't prevent all stress, minimizing unnecessary sources gives the pregnancy the best chance.

The prognosis following pregnancy loss depends significantly on the cause identified and the mare's individual reproductive history. If chromosomal abnormality caused loss, this was likely a random occurrence with minimal recurrence risk. If infection caused loss and you've vaccinated and implemented biosecurity, future risk is reduced. If progesterone insufficiency was identified, supplementation during future pregnancies offers excellent hope for success. Mares with single pregnancies losses have excellent success rates with subsequent pregnancies, often exceeding 90 percent if appropriate preventive measures are taken.

For mares with recurrent losses, the challenge becomes more complex but not hopeless. Some mares have anatomical issues or persistent health problems that require creative management. These mares may benefit from referral to an equine reproduction specialist who can perform detailed diagnostic work and design individualized breeding protocols. Some recurrently unsuccessful mares eventually carry foals to term when appropriate interventions are implemented. Others may need to be retired from breeding if their specific problems can't be overcome, though many can still be valued as riding or companion horses. Understanding your mare's specific situation with veterinary guidance helps set realistic expectations and determine appropriate next steps.