High Risk Pregnancy in Mares
There is often a large investment, financial and emotional, involved in the breeding and pregnancy maintenance of a mare. Studies have shown that between 25 and 40 percent of mares that are bred fail to produce a live foal. Many reasons exist for this failure to produce healthy offspring. Some of the reasons include:
- Embryonic loss
- Perinatal death
The causes of abortion, stillbirth and perinatal death in horses are many. In a study conducted in Kentucky by Giles and coworkers, 3,527 cases were investigated. The most common cause of loss of the foal was placental infection caused by bacteria, equine herpes virus, fungi or unknown organism. The second most common cause of death was due to complications at birth, such as neonatal asphyxia, dystocia (difficulty delivering) or trauma. Premature separation of the placenta, twinning, and congenital anomalies were also common.
In some cases, mares with these potential problems can be identified during pregnancy on the basis of their history. They are referred to as high risk mares and are at high risk for serious problems that may compromise their chance for survival during the critical period, from around 300 days gestation onward. Though all mare/foal units should receive the best care and management, pregnant mares at higher risk should be identified. Because a mare or foal is considered at risk, it does not mean that they will definitely get sick and require intensive care. Many do not. However, it is important to have a heightened sense of awareness about the high risk mare's well being, and in some cases, precautionary actions are recommended.
Mares that are experiencing a problem with the current pregnancy or who have had abnormal pregnancies in the past are potential high-risk candidates. For example, twins, illness, weight loss, surgery, anesthesia, and any other major stress during the current pregnancy contribute to risk. In past pregnancies, dystocia, twins, delivery of sick, premature or unusual foals, retained placenta, agalactia (lack of milk production), grazing on tall fescue, infections, untimely vaginal discharge or lactation, or frank illness in the mare during or after pregnancy, put the mare in the high-risk category.
Besides the historical information that is important in identifying the high-risk mare, certain clinical signs are indicative of problems during the current pregnancy. These would include the following:
- Premature udder development
- Premature lactation
- Vulvar discharge
If any of the above signs are observed, the mare requires special consideration. The special consideration that the mare should receive depends on your veterinarian's physical examination and diagnosis. Specific treatment is dependent on a specific diagnosis. Certain diagnostic procedures are helpful in determining more specifically what the problem is, and predicting their contribution to potential problems during delivery or after.
When monitoring pregnancy in the high risk mare, each mare is should be treated as an individual. The minimum level of care for the high-risk mare is the close monitoring of the mare until parturition occurs and an attended birth. Placental infections should be treated with appropriate antibiotic therapy. Monitoring usually includes:
- Palpation per rectum
- A vaginal speculum examination
- Transabdominal ultrasound examination
- Fetal heart rate determination
- Mammary (udder) development
If you have a high risk mare, the first thing to do is to make your veterinarian aware of the problem if he doesn't already know. Second, you should plan on monitoring the mare closely, at least three times a day. You should look for signs of udder development or premature lactation, evidence of impending parturition (loosening of ligaments around the tail, elongation of vulva), vaginal discharge, restlessness, or strange behavior. Sometimes you can observe sweating or signs of colic.
At the time of foaling, an experienced person should be available. If an experienced person is not available, you should consider moving the mare to a facility. You should also prepare a foaling kit that includes a tail wrap for the mare, a bucket for water and disinfectant for washing the mare, dry towels to wipe the foal, scissors to open the placenta if it does not break and 2 percent iodine or chlorohexadine to dip the umbilicus of the foal at birth.
The identification of a high-risk pregnancy may be more obvious as in the case of twins or placentitis or it may be difficult in an instance such as placental insufficiency or neonatal asphyxia (oxygen starvation). History is the first place to look for clues, both the past reproductive history and the current events in this mare's life. A past history of foal loss automatically places the mare in a higher risk category than a mare that has had previously uncomplicated pregnancies. Previous uterine infections, twinning, and malpositioning of the foal may develop again. While a previous difficult birth may create complications that effect subsequent pregnancies or foalings, it is not necessarily going to recur or put the mare at risk. It just depends on the nature of the problem. For example, a giant foal creates problems at delivery, but does not create risk for subsequent deliveries unless the mare was injured in the process.
A history of previous foals with failure of passive transfer or sepsis may suggest that the mare does not produce adequate colostrum. In mares that have produced foals with neonatal isoerythrolysis (a condition related to antibodies against the foals red blood cells-RBC), there is a concern that they may also produce antibodies against the RBCs of the current foal that she is carrying. A prior Cesarean section or fetotomy may have damaged the uterus/cervix resulting in a difficult delivery.
Valuable information from the current gestational history is also important in high-risk pregnancy identification. Was there a suspicion of a double ovulation at breeding or twin pregnancy in earlier checks? Has the mare been exposed to equine herpes virus, equine viral arthritis or Ehrlichia risticii (infections that may produce weak or dead foals)? Has the mare been grazing on fescue pasture? Fescue pasture that is infested with an endophyte (fungus) causes prolonged gestation, difficult foaling and agalactia (no milk production) in the mare. Did the mare have endometritis (uterine infections) before she was bred? Has the mare been clinically ill or colicky during her pregnancy? If you answer yes to any of the above questions, then the mare should receive special consideration.
Conditions associated with high risk pregnancies or foals can be due to maternal problems, neonatal problems or conditions of labor or delivery. They are as follows:
- Premature udder development and colostral leakage
- Purulent vaginal discharge
- Colic surgery
- History of foal with isoerythrolysis
- History of foal with maladjustment syndrome
- Poor nutritional status
- Prolonged transport before parturition
- Meconium-stained fluid
- Premature placental separation
- Inadequate colostrum ingested
- Delayed standing or nursing
Labor and Delivery
- Premature parturition
- Prolonged gestation
- Prolonged labor
- Induced labor
- Early umbilical rupture
- Cesarean section
Early mammary development and dripping of colostrum (before 320 days gestation) are signs of impending premature birth. The differential diagnosis for these signs should include possible twinning and placentitis. Twinning can sometimes be ruled out on the basis of a transabdominal ultrasound, which allows for non-invasive monitoring of the late term fetus. Images of the late term foal can usually be obtained at the most ventral area of the mare's abdomen. The most recognizable feature of the foal is his thorax where the shadows of the ribs can be detected. From this point the beating heart can be observed. Information that can be gained from the ultrasound include the presence of twins, the approximate size of the fetus, the fetal heart rate, the placental thickness and a gross evaluation of the allantoic fluid volume.
Fetal heart rates vary between 70 to 110 beats per minute. One evaluation of fetal heart rate only gives you a moment in time picture. Repeated monitoring is a better predictor of fetal health. Persistent fetal tachycardia (over 110 beats per minute) is an indicator of fetal distress. The presence of two different fetal heartbeats confirms the presence of twins. It is sometimes difficult to know for sure that you are looking at two separate heartbeats because an active foal moves around the abdomen constantly.
The vulvar discharge and fever in the mare are compatible with placentitis. Both bacteria and fungal organisms can infect the placenta. It is felt that the route of entry for infectious organisms is generally ascending through the cervix, though it is possible that infection could have occurred at breeding or through a hematogenous (blood) route. Beta-hemolytic Streptococci and Escherichia coli are the most commonly cultured bacteria from a placentitis, while Aspergillus is the most incriminated fungal organism. The foal is at risk of developing an in utero infection in mares with placentitis. The bacteria can pass through the placenta to infect the foal. This infection may weaken or kill the foal. The inflammation associated with the infection may result in a premature delivery of the foal.
Prematurity in the foal can be accompanied with myriad of problems, in particular, problems associated with the respiratory tract. Surfactant, a phospholipid compound, is produced in the lungs of foals in late gestation. Surfactant acts to decrease surface tension in the alveoli and aids the inflation of the lungs. A total lack of surfactant leads to increased respiratory effort, pulmonary edema and hyaline membrane formation. This is generally known as respiratory distress syndrome, and equine neonatalogists have had little success in saving the truly premature foal.
Prematurity has been defined as a gestational age of less than 320 days. This technical division between prematurity and maturity does not stand up in all cases. Readiness for birth is a better concept in looking at prematurity and immaturity. A foal induced at 330 days gestation may not be ready for birth even though it is more than the technical 320 days. If it were not going to be born naturally until 350 days gestation, then it would be at high risk for respiratory distress syndrome. Whereas, this foal born at 312 days gestation was ready to be born in regards to its pulmonary function. It is hypothesized that chronic maternal stress, such as twinning or placentitis, actually acts to hasten lung maturity.
Small size and the laxity of flexor tendons are usually signs of immaturity or dysmaturity in a foal but may also be seen in the post-mature foal (gestation over 360 days). Post-mature foals are often small and emaciated. A thin body condition is probably a result of placental insufficiency or intrauterine growth retardation (IGR). The foal is essentially starved in the uterus because the maternal nutrients are not able to cross the placenta. Gestations over 360 days should be considered a high-risk pregnancy.
Lack of colostrum from the mare or failure to nurse within three hours of age are potentially high risk factors. If frozen colostrum from another mare can be obtained, then it is the best way to give this foal passive immunity. Otherwise, plasma transfusions are the best alternative. Prophylactic antibiotics are important in case there is a pre-existing infection.
There is no way to really predict malpositioning of the foal during delivery. While in the uterus the foal is quite active and changes position frequently. During the first stage of labor, the normal foal assumes the position of front feet first, head on carpus. Any deviation from this position may cause a delay in the progression of the delivery. During the delay the foal may become distressed. This distress will sometime lead to expulsion of meconium (the foal's first fecal matter) while the foal is still in the uterus. In the foal's attempts to breathe it may breathe in the meconium contaminated amniotic fluid. This is a serious complication that could lead to severe respiratory problems in the newborn.
Treatment For Placentitis
- Antibiotic administration
- Anti-inflammatory drugs
- Progesterone-type drugs
- Stall rest
Systemic antimicrobial therapy is important in the treatment of bacterial placentitis in mares. The effects of pregnancy on drug distribution are unknown in the mare. In pregnant women, drug levels can be reduced 10-50 percent due to various pharmacological reasons, such as an increase in volume of distribution and an increase in drug metabolism. The recommendations in humans are to increase the dose or dosing interval by 25-50 percent. This should not be done when using aminoglycosides due to their kidney toxicity. Penicillin, cephalosporin and trimethoprim sulfas would be the safest choices.
Using an antimicrobial that crosses into the foal would also be important because septicemia occurs in 80 percent of the aborted fetuses with acute placental lesions. In one study, the investigator measured concentrations of penicillin, gentocin and trimethoprim sulfa in amniotic, allantoic and foal plasma/serum after administration to the mare and found that only trimethoprim sulfa was detectable. It is possible that placentitis may enhance the passage of other drugs through the placenta, but this is not known.
Increases in prostaglandins (inflammatory products that induce birth) have been associated with early parturition in the pony mare. Flunixin meglumine (Banamine®) is a potent anti-inflammatory drug that inhibits the release of prostaglandin F2a. Its use in placentitis is an attempt to delay parturition. Altrenogest, a synthetic progestagen, can be added to the regime. Though its use is sometimes controversial, it is felt to maintain possibly low maternal progesterone levels and prevent abortion. Mares have been known to foal while on Altrenogest, so there was little fear that the pregnancy would be maintained beyond a safe time for the foal. Stall rest is important until clinical signs resolve.
For the diagnosis of twinning, there is no specific treatment. Some veterinarians feel that anti-inflammatory drugs and progesterone-type drugs are helpful in maintaining the pregnancy to a more mature state. It is extremely important to attend the birth of twins so the mare should be monitored closely. It is difficult to predict the timing of birth of twins. Generally twins come early. If the foals are near term, they may have a dystocia (difficult delivery) due to their size or the possibility of both coming at the same time.
Malpositioning of a foal often results in a dystocia. Normal foals are delivered front feet first with the foal's head resting on his knees (carpus). A malposition is any position other than this. The foal may come upside-down, hind legs or tail first or one leg or head bent back. It is sometimes hard to determine the exact orientation of a malpositioned foal because of the tight quarters in the uterus. Your veterinarian will attempt to palpate the foal and reposition him for a normal delivery. This is an emergency situation because the foal needs to be delivered within 30 minutes of the mare breaking water or the foal will die from lack of oxygen.
If the foal is delivered and you notice that the amniotic fluid is yellow-tinged then you should suspect meconium aspiration. You should immediately wipe out the foal's nostrils and mouth. Suspending the foal from his hind legs and gently hitting him on the chest with a cupped hand (coupage) will help to expel more of the meconium-contaminated fluid from the lungs before he begins to breathe regularly.