Placentitis

Placentitis, inflammation of the placenta in pregnant mares, represents one of the most serious reproductive emergencies affecting equine pregnancy. Left untreated, placentitis often results in abortion, sometimes late in pregnancy when foal viability becomes possible and loss becomes devastating. The disease can be subtle in early stages, with few obvious signs before abortion occurs if the condition progresses undetected. Understanding that placentitis can develop in any pregnant mare, recognizing early warning signs, and maintaining vigilant monitoring during late pregnancy allows early detection and treatment that prevents abortion in many cases.

The placenta serves critical functions in equine pregnancy including nutrient and oxygen transfer to the developing foetus. Inflammation of placental tissue compromises these essential functions, depriving the foetus of necessary nutrients and oxygen. As inflammation progresses, the nutritional support becomes increasingly inadequate until the foetus cannot survive, triggering abortion. The speed of progression varies, with some cases developing slowly over weeks while others escalate rapidly over days. Early detection allows intervention with antibiotics and other treatments that sometimes stop progression and allow pregnancy to continue.

Ascending infection through the cervix and uterine body represents the most common route by which bacteria reach the placenta. Mares with cervical incompetence, uterine abnormalities, or previous uterine infections face increased risk. Environmental bacteria or organisms from the mare's genital tract can ascend during heat cycles or during periods when normal cervical competence is compromised. Stallions with urethral infections can introduce bacteria during breeding, though this represents a less common transmission route than ascending infection from the mare's own flora.

Hematogenous infection, where bacteria reach the placenta through the mare's bloodstream, represents another infection route particularly in cases involving systemic infection. Mares with bacterial infections elsewhere in their body sometimes develop placentitis through bacterial seeding of the placenta. Respiratory infections, strangles, or other systemic infections can occasionally lead to placental involvement. This transmission route is less common than ascending infection but produces similar clinical outcomes.

Seasonal patterns in placentitis incidence remain somewhat unclear, though some studies suggest increased cases during certain times of year. Some authorities suspect dormant herpes virus reactivation triggered by seasonal stress might contribute to placentitis. Others note apparent clustering of cases in certain facilities or geographic areas suggesting environmental factors might play roles. Understanding potential risk factors guides preventive strategies during high-risk periods.

This guide will help you understand placentitis pathology, recognize early warning signs that warrant veterinary investigation, understand what treatments might save pregnancies, and implement preventive strategies reducing disease risk. You'll learn about monitoring during late pregnancy, how to recognize discharge or other signs warranting veterinary attention, and what interventions improve pregnancy outcomes. Armed with this knowledge, you can maintain pregnancies at risk and maximize the chances of healthy foal delivery despite placentitis development.

Bacterial infection represents the most common cause of placentitis, with various bacteria including Streptococcus species, Escherichia coli, and others ascending into the uterus and affecting the placenta. Mares with vaginal or cervical infections face higher risk of ascending bacteria reaching the uterine environment. Poor hygiene during breeding, breeding with contaminated stallions, or breeding into contaminated conditions increases bacterial exposure. Some bacteria reside normally on genital skin and only become problematic when vaginal or cervical barriers fail. Environmental bacteria from stall bedding or pastures can ascend into the reproductive tract.

Viral infection, particularly equine herpes virus (EHV-1), can cause placentitis sometimes without obvious maternal signs. EHV-1 is particularly concerning because it causes placental disease with minimal fever or systemic signs in the mare, making the infection easily missed. Abortion from EHV-1-induced placentitis can occur suddenly in apparently healthy mares. Other herpesviruses and additional viral agents might occasionally cause placentitis, though bacterial infection remains more common. Viral placentitis sometimes occurs in mares with previous herpes exposure when dormant virus reactivates.

Fungal infection of the placenta represents a less common but serious cause of placentitis. Fungal organisms including Aspergillus species and others can ascend into the uterus and establish placental infections. Fungal placentitis tends to develop slowly and might be resistant to standard antibiotic therapy. Environmental exposure to fungal spores increases risk, particularly in facilities with mold or moisture problems. Some mares appear more susceptible to fungal infections than others. Moldy hay or bedding containing fungal spores can increase exposure risk.

Cervical incompetence predisposes mares to placentitis by allowing ascending infection. Mares with scarring from previous infections, trauma during breeding or delivery, or anatomical abnormalities that prevent complete cervical closure face higher risk. Some breeds or individual mares have inherent cervical weakness. Identifying mares with cervical problems allows implementing preventive cervical cerclage or other interventions during pregnancy. Aging also affects cervical competence in older mares.

Previous uterine infection increases placentitis risk, as bacteria might persist in the uterus despite treatment of previous infections. Mares with histories of retained placenta, intrauterine infection, or repeated reproductive failures face higher risk. Some mares seem susceptible to chronic low-level uterine infection that flares during pregnancy. Understanding your mare's reproductive history guides assessment of placentitis risk. Mares with multiple past infections warrant extra monitoring during pregnancy.

Environmental factors including facility hygiene, bedding quality, and water quality influence infection risk. Mares in facilities with good hygiene and appropriate environmental management show lower disease incidence. Dusty, dirty bedding or poor water quality increases risk of respiratory or gastrointestinal infections that might secondarily affect the placenta. Some disease outbreaks cluster in specific facilities, suggesting environmental risk factors play roles. Seasonal variations in disease occurrence might relate to environmental stress factors.

Vulvar discharge represents an important warning sign of placentitis, with any vaginal discharge in a pregnant mare warranting investigation. The discharge might be clear and watery, thick and mucoid, or yellowish. The character and amount of discharge vary depending on infection severity and duration. Any discharge beyond the normal minimal amounts pregnant mares might show warrants veterinary evaluation. Some discharge is minor and easily missed unless the mare is specifically examined.

Premature udder development, where the mammary gland enlarges earlier than expected in pregnancy, suggests placental compromise. Normally mares develop udder tissue gradually as pregnancy progresses, with significant development in the final weeks. Premature udder enlargement sometimes appears with placentitis and might indicate impending abortion. Monitoring udder development throughout pregnancy helps identify abnormal patterns.

Milk loss before delivery, where colostrum or milk drips or streams from the mare's teats before labor, indicates serious placental compromise. This happens when the placental barrier breaks down enough to allow fluid and electrolytes to leak from the fetus into the mare's circulation, triggering false labor signs and milk production. This sign indicates immediate veterinary attention is needed, as abortion might be imminent.

Lactation outside of foaling represents an emergency sign requiring immediate veterinary attention. If mares lactate and expel milk weeks or months before expected foaling, abortion is likely imminent. This sign indicates the foetus has been dead or non-viable for some time, and expulsion will likely occur soon. Identification of lactation despite premature timing warrants rapid veterinary involvement.

General illness signs including fever, lethargy, or increased respiratory rate sometimes appear with placentitis. Some mares develop obvious systemic signs while others remain apparently healthy despite significant placental disease. The absence of systemic signs doesn't exclude placentitis. Regular temperature monitoring helps identify subtle fever that might indicate infection.

Behavioral changes during late pregnancy sometimes indicate placental problems. Mares might show irritability, restlessness, or changes in eating and drinking. Some mares display repeated false labor signs with contractions and straining that resolve without foaling. These behavioral changes warrant veterinary evaluation to determine whether they represent normal pre-labor behavior or signs of placentitis.

Ultrasound examination of the placenta provides valuable diagnostic information, revealing fluid accumulation, placental thickening, or other signs of inflammation. Transrectal or transabdominal ultrasound allows visualization of the placental layers and identification of abnormalities. Placental thickness greater than normal measurement suggests inflammation. Fluid accumulated between placental layers indicates disease. Ultrasound findings guide treatment decisions and provide prognostic information about likely pregnancy outcomes.

Transcervical uterine culture attempts to identify infectious organisms causing placentitis. This procedure involves passing a sterile swab through the cervix to obtain samples from the uterine environment. Culture results identify the specific organism involved, guiding antibiotic selection. The culture process takes several days, requiring treatment to begin based on suspected organisms while awaiting results. Obtaining cultures early improves likelihood of identifying the causative organism.

Placental biopsy, obtained through the vaginal approach using specialized instruments, provides direct tissue samples for identification of inflammation and organisms. Histological examination of placental tissue helps confirm diagnosis. Culture of placental tissue sometimes identifies organisms that blood cultures or uterine cultures might miss. While more invasive than ultrasound, placental biopsy provides definitive diagnostic information.

Antibiotics represent the primary treatment for bacterial placentitis, with broad-spectrum antibiotics given systemically until culture results guide more specific therapy. Intravenous antibiotics achieve better placental penetration than oral medication, making IV therapy preferred for serious infections. Aminoglycosides, fluoroquinolones, and other classes work against common equine bacteria. Treatment continues for weeks to allow resolution of infection and placental healing.

Suppressive therapy including progestin supplementation helps maintain pregnancy once placentitis is diagnosed. Altrenogest administered orally or injectable progesterone supports the pregnancy even if it would normally be aborted. Supplementation sometimes allows progression to viability or full-term delivery despite placental infection. The combination of antibiotics and progestin therapy improves abortion prevention compared to either treatment alone.

Symptomatic treatment including anti-inflammatory medications reduces placental inflammation and improves blood flow. Non-steroidal anti-inflammatory drugs (NSAIDs) help manage inflammation. Some protocols include oxytocin administration to enhance uterine blood flow and placental support. Management of secondary complications including electrolyte imbalances or other systemic effects supports mare health during treatment.

Stall rest during treatment allows the mare to conserve energy while her body fights infection. Complete exercise restriction prevents stress that might trigger abortion. Stall confinement should be comfortable with appropriate bedding and protection from environmental stress. Some mares benefit from being able to see other horses to reduce anxiety. The duration of rest continues through treatment completion and should extend until ultrasound confirms resolution of placental disease.

Nutrition support during placentitis treatment ensures adequate calories and nutrients for the mare to maintain pregnancy while fighting infection. Good quality hay and appropriate grain or pellets provide balanced nutrition. Vitamin and mineral supplementation might be recommended. Weight loss during treatment should be minimized as maternal condition affects fetal viability. Nutritional support contributes to successful pregnancy maintenance alongside medical treatment.

Monitoring during treatment includes regular ultrasound examination tracking placental changes and confirming treatment effectiveness. Repeat ultrasounds at intervals help assess whether placental thickening is resolving and inflammation decreasing. Increasing placental disease despite treatment indicates treatment failure or resistant infection requiring alternative approaches. Serial monitoring guides decisions about continuing current therapy or implementing changes.

Vulvar discharge monitoring helps assess treatment response. Discharge that appears in early placentitis cases should decrease and resolve as treatment takes effect. Persistent discharge despite antibiotics might indicate inadequate treatment or resistant infection. Quantifying discharge changes helps assess whether treatment is working.

Mare comfort management including pain relief and management of inflammation supports treatment success. Anti-inflammatory medications already discussed help with this. Adequate bedding and comfortable stalling reduce stress that might exacerbate disease. Some mares benefit from tranquilization if they show excessive stress or false labor signs.

Preparation for potential foaling becomes important as delivery approaches. Having foaling supplies ready, ensuring access to veterinary care, and arranging foal intensive care support (if needed) helps prepare for successful delivery. If full-term delivery is achieved, the foal might benefit from intensive care including high-quality colostrum replacement if the mare hasn't produced adequate colostrum.

Preventing placentitis requires attention to reproductive tract health and cervical competence throughout pregnancy. Good hygiene during breeding, proper Mare selection with attention to prior reproductive problems, and careful stallion selection avoiding those with urethritis all reduce infection risk. Some mares benefit from cervical cerclage during pregnancy to improve cervical competence if previous history indicates risk.

Screening for reproductive tract abnormalities before breeding allows identifying mares at high risk. Mares with poor cervical competence, previous intrauterine infections, or other anatomical issues might benefit from special management during pregnancy. Some high-risk mares might be managed with prophylactic antibiotics or other preventive measures during pregnancy.

Hygienic breeding practices including clean facilities, clean stallions, and appropriate hygiene protocols reduce bacterial exposure. Avoiding breeding mares during heat if vulvitis or other genital tract infection is present prevents introduction of contaminated bacteria into the reproductive tract during breeding.

Early detection through regular monitoring during late pregnancy allows identification of placentitis before abortion occurs. Mares showing any discharge, udder changes, or behavioral changes warrant immediate investigation. Ultrasound evaluation of mares with any concerning signs allows diagnosis before disease progresses.

Herpes vaccination protocols might provide some protection against EHV-1-induced placentitis in vaccinated mares. Vaccination doesn't guarantee prevention but reduces risk and might reduce disease severity if infection occurs. Vaccination according to current recommendations provides baseline protection for mares prone to herpes infection.

Prognosis for placentitis varies based on organism type, disease severity, timing of treatment, and mare age or health status. Mares identified early and receiving appropriate treatment have reasonable chances of preventing abortion and continuing pregnancy. EHV-1-associated placentitis shows more guarded prognosis than bacterial infections. Some mares deliver viable foals despite placentitis, while others abort despite aggressive treatment. Overall success rates in preventing abortion with early identification and treatment range from modest to reasonably good depending on circumstances.