In the Aftermath of Birth--Retained Placenta
The birth of a foal is a wondrous event; if all goes well, it is over quickly as the mare goes through the three stages of labor. The first stage generally involves restlessness as the mare paces the stall, paws, lies down, gets back up, and perhaps breaks into a sweat. The second stage, which includes "breaking her water," is one of strong contractions as the mare lies down to deliver the foal, often in a matter of only a few minutes. Once the foal is safely delivered, there might be temptation for the owner to lower his or her guard, from an observational standpoint. However, there is another very important stage yet to go and it is highly important. It is the third stage of labor, when the placental membranes are expelled.
The expulsion takes place as the mare, in essence, continues in labor with strong uterine contractions. Normally, the expulsion of fetal membranes will occur within an hour after birth, but sometimes part or all of the placenta is retained.
The condition of retained fetal membranes, says M.H.T. Troedsson, DVM, PhD, Dipl. ACT, service chief of the reproduction department and professor in the Department of Large Animal Clinical Sciences at the University of Florida, is defined as the failure of the entire or partial fetal membranes to be expelled beyond three hours after foaling. (Troedsson presented "Fetal Membrane Retention and Toxic Metritis" at the Equine Symposium staged by the Society for Theriogenology in November 2000.)
Sometimes the entire placenta is retained; in other cases bits and pieces might remain in the uterus. The only way to know for sure if the entire placenta has been expelled is to examine it closely after expulsion. If tears have occurred and pieces seem to be missing, there is a likelihood that some of it remains within the uterus.
The problem is complicated by the fact that it sometimes is difficult to determine what is normal and what is abnormal in an expelled placenta. Minor tears can be tough for a horse owner to see. If there is any doubt, consult a veterinarian without delay.
The reason for urgency, says Troedsson, is that infection can set in quickly and the result can be toxic metritis (inflammation of the uterus), followed by laminitis. The window of opportunity to remove retained membranes before the infection process begins is relatively small--from immediately after birth to 12 hours post-partum.
"After 12 hours," he says, "there is cause for concern if retained membranes are still attached to the uterus. If they remain within the uterus 24 hours after birth, there is grave concern for the mare's health."
The endometrium (inner layer of the uterus) is attached to the outer layer of the placenta by the placenta's villi, small vascular (supplied with blood vessels) projections. The villi remain attached to the uterine wall throughout the pregnancy. According to Troedsson, expulsion of the placenta works like this: The process for separation of the villi from the uterus probably begins with rupture of the umbilical cord, which occurs during or just after the birthing process.
"Rupture of the umbilical cord in association with parturition is believed to cause collapse of the fetal placental vessels, with subsequent shrinkage of the chorionic villi," reports Troedsson.
As the villi lose their grip, contractions stimulated by oxytocin and possibly prostaglandin (both hormones produced by the mare's body) work to expel the membranes.
"Myometrial (uterine muscle) contractions reduce the uterine size and the amount of circulating blood in the endometrium, resulting in relaxation of the endometrial crypts (that the villi fit into), which allows the villi to be released," he says.
Dystocia, which refers to a compromised and difficult birthing process, often is implicated in a retained placenta. Abortions also can be implicated, according to Troedsson. Sometimes, he says, the uterus is simply too fatigued after a difficult delivery to continue the contraction process that expels the placental membranes. There are other causes as well, Troedsson says, but not all of them are understood.
"The cause of retained fetal members after term delivery of the equine fetus," he says, "is believed to be an endocrine imbalance or disturbance in normal uterine contractions. But any swelling at the site of the microcotyledons (where the villi attach) can cause retention of the fetal membranes."
As mentioned, sometimes the retention is complete and sometimes it is partial--meaning that only a portion of the placenta is retained. Interestingly, Troedsson says, "The most common site of partial retention is the non-gravid (non-pregnant) horn."
Membrane retention can cause some potentially devastating reactions. When there is any retention, according to Troedsson, the uterus is unable to involute (shrink in size), while at the same time cells of the retained membranes are disintegrating, with rapid bacterial growth resulting.
"Rapid bacterial growth within the uterine lumen (cavity) occurs immediately post-partum, and resorption of toxins from the uterus results in toxic metritis (inflammation of the uterus). Toxic metritis is characterized by the accumulation of bacteria, toxins, and inflammatory fluid within the uterine lumen. Since Gram-negative organisms (a class of bacteria) often are involved, the condition frequently results in endotoxemia and laminitis."
Diagnosis usually is easy if the entire placenta is retained, because membranes often will be hanging from the vulva three hours or more afer foaling. It might not be quite as easy with partial retention if membranes have been passed, but parts remain in the uterus with no outward indication.
Troedsson says, "If the fetal membranes remain within the uterus without being visible, as in cases of partial retention of fetal membranes, a thorough clinical examination is required for diagnosis. Following the expulsion, the fetal membranes should be spread on a flat surface and examined to determine their entirety and integrity. Tears, missing areas of tissue, and areas of chorionic surface (the highly vascular outer fetal membrane) devoid of microvilli should be considered evidence of partially retained fetal membranes. Evidence that a portion of the placenta is retained in the uterus is indication for transvaginal digital examination and institution of proper therapy."
Rectal examination and ultrasonography are also helpful in determining the degree of uterine involution or shrinking, he says.
While long-term fetal membrane retention can be devastating to the mare's good health, there often are few outward indications that an infection might be raging during the very early stages.
"Vital signs are often normal in early cases of retained fetal membranes, but systemic signs may accompany fetal membranes retained for more than 24 hours," says Troedsson. "The uterine wall (in the latter stages) is thin and often necrotic. A red-brown, often fetid vaginal discharge is commonly seen in these mares. Systemic signs of depression, accompanied by neutropenia and leukopenia (reductions in the number of neutrophils and white blood cells, respectively, in the blood), are apparent with the development of endotoxemia."
The question that now presents itself is this: What should be done to remove the retained membranes before they can wreak the havoc described above?
Treatment of Complete Retention
First, if the membranes are hanging from the mare's vulva, they should be knotted in such a way that she doesn't step on them.
Troedsson discourages the use of traction, or pulling the membranes. Worst-case scenario, he says, could be uterine prolapse if undue force is used. More likely, however, forcible removal could result in retention of microvilli in the endometrial crypts, and that would set the stage for toxic metritis. Manual removal can also result in hemorrhage and death.
"These complications," says Troedsson, "may result in undesirable uterine inflammation, delayed uterine involution, and possible permanent endometrial damage with subsequent lower fertility."
The next steps should be in the hands of a veterinarian because, as Troedsson says, "Clinical judgment will decide which method to use in an individual case. As a general rule, the least invasive method that results in the expulsion of the fetal membranes should be employed."
Following is Troedsson's recommended treatment approach when there has been a complete retention of fetal membranes. He divides the treatment protocol into three stages or categories, depending on the time involved in the retention.
Step 1 is employed for membranes retained three to eight hours post-partum. At this stage, Troedsson recommends repeated oxytocin treatments administered either intravenously or intramuscularly every one to two hours, up to eight hours post-partum or until the membranes are expelled.
Step 2 is employed when fetal membranes have been retained for more than eight hours. Involved in this treatment protocol is the slow intravenous infusion of oxytocin in saline over 30 to 60 minutes, followed by five to 10 minutes of walking.
Step 3 is employed if the above two steps fail to result in fetal membrane expulsion. This step involves the infusion of large amounts of sterile water or a weak (less than 2%) povidone-iodine solution in water into the allantoic space. In order for this treatment approach to be successful, Troedsson emphasizes, the allantochorion (inner lining of the placenta) needs to be intact so that the fluid does not leak out. In conducting the procedure, a stomach tube is inserted through the torn end of the cervical star (uterine end of the cervix) and into the allantoic space.
"The membranes," says Troedsson, "are then manually closed over the tube and fluid is infused into the allantoic cavity until the mare exerts abdominal pressure. Up to four gallons of solution may be infused using this method. The distension of the allantoic cavity causes forceful myometrial contractions, which results in the expulsion of the fetal membranes.
"However, repeated infusions may be necessary before a complete expulsion of the membranes is accomplished. The procedure results in the endogenous (within the mare's system) release of oxytocin, at the same time as the endometrium is stretched, which will facilitate the release of microvilli from the endometrial crypts."
This approach, says Troedsson, has produced excellent results even beyond 12 hours post-partum.
Partial Retention of Membranes
In this situation, Troedsson divides the approach into two categories--when the retained membrane can be reached manually and when it cannot be reached.
"If a small piece of allantochorion can be reached by a transvaginal approach, 10-20 IU of oxytocin can be administered intravenously, followed by very careful traction of the retained membranes over 10 to 20 minutes," he says. "This method often results in successful removal of the retained pieces without complications." However, Troedsson again warns against using too much force to avoid retention of the microvilli.
He offers the following approach when the retained membranes can't be reached: "If no pieces of the partially retained fetal membranes can be reached by a transvaginal approach, the uterus should be lavaged daily, with sterile water, isotonic saline, or a dilute--less than 2%--povidone-iodine solution. The uterus should be lavaged daily until all remaining pieces of the fetal membranes have been expelled, or, if this cannot be determined, until the recovered lavage fluid is free from debris. Intrauterine lavage should be combined with systemic antibiotics and anti-inflammatory treatments."
Troedsson says broad-spectrum antibiotics effective against Gram-negative microorganisms should be used. Intrauterine antibiotics can sometimes have negative side effects, such as irritating the endometrium. But they can also be beneficial in the battle against proliferating bacteria.
Troedsson also recommends using drug therapy to promote continued shrinking or involution of the uterus along with administration of drugs to battle inflammation, endotoxemia, and laminitis.
Odds and Ends
Do certain types of horses have more of a tendency toward fetal membrane retention than others? Yes, says Troedsson. Draft mares seem more prone to the problem than light horse breeds.
His assessment is backed by a report presented at the 2000 Theriogenology Symposium by D.A. Freeman, DVM, PhD, of the University of Massachusetts. Freeman reported on a survey of ranches in central Canada and North Dakota, which was conducted over two years and included more than 16,000 mares. The breakdown of mares involved was as follows: 7,901 light horses, 2,210 crossbreds, and 6,213 draft mares.
Of that number, 4.7% of the draft mares retained fetal membranes compared to 1.4% of the crossbreds and 0.9% of the light horse mares. The reported increase of retained fetal membranes was markedly higher, says Freeman, following assisted delivery, birth of a dead foal, or birth of a foal which died shortly after birth.
The Next Generation?
The next question concerns fertility of mares which have retained fetal membranes: Is it compromised? There is no blanket answer, says Troedsson, because much depends on the degree of trauma and the way in which it was resolved.
Generally speaking, he says, there should be little effect on reproductive capability if the problem is properly resolved during the 12-hour or less window of opportunity. However, improper management and retention after 24 hours, he believes, could compromise reproductive health.
The take-home message is that retained fetal membranes pose a serious danger to the mare's reproductive health and her life. If a problem is even suspected, veterinary help should be sought immediately.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals