SeÁn A. Finan, Angus O. McKinnon
Postpartum Complications in Broodmares
SeÁn A. Finan, Angus O. McKinnon
The postpartum period is a critical period in the mare’s reproductive process because complications can be life threatening for the mare or significantly affect subsequent fertility.
Peripartum hemorrhage is a serious complication in the mare and can become fatal in a short period of time. The middle uterine artery is most commonly the source of hemorrhage, but the external iliac, utero-ovarian, and vaginal arteries can also be involved. Hemorrhagic events may arise any time during late pregnancy but are most common in the first 24 hours after foaling. Postpartum hemorrhage is responsible for up to 40% of fatalities associated with foaling and can occur in mares of any age, but older mares are at higher risk. Mares may hemorrhage into the broad ligament of the uterus, directly into the abdominal cavity, or both, and the origin of the hemorrhage and the point at which clinical signs are recognized likely affect the prognosis for survival.
Hemorrhaging mares have various clinical signs, which can range from signs of colic accompanied by pallor, tachycardia, a weak pulse, and cold extremities, to few or no outward signs or signs that are attributed simply to postfoaling uterine contractions. Some mares may also appear depressed, show flehmen, vocalize, and have muscle fasciculations.
Diagnosis is often obvious and can be made on the basis of clinical examination; however, in some instances clinical signs are obscure and cases may remain undiagnosed until a hematoma in the broad ligament is discovered at a later reproductive examination. Both rectal and transabdominal ultrasonography are very useful in identifying the source of the bleeding. Hemoabdomen has a swirling ground-glass appearance ultrasonographically and can be appreciated readily with a 5-MHz rectal probe used transabdominally. A vaginal exam should be performed to identify concurrent problems that may result in detection of blood in the vagina or uterus, or other abnormalities. Abdominocentesis may be useful, but it must be remembered that blood will be obtained if the spleen is inadvertently punctured. Hematologic parameters must be interpreted with care because many mares with significant and life-threatening bleeding initially maintain a normal packed cell volume as a result of splenic contraction and vasoconstriction. Assessment of the degree of hypoproteinemia is often useful, and occasionally, measurement of systemic lactate may be helpful.
The treatment plan for a hemorrhaging mare presents a conundrum for the practitioner. Heart rate and clinical signs relative to the time after foaling can be good indicators of survival and may also help dictate therapy. A mare with a heart rate higher than 90 beats/minute and clinical signs developing within 12 hours of foaling has a poorer likelihood of survival than a mare that has a heart rate of 65 beats/minute and signs that arose 24 hours after foaling. Many mares respond favorably to conservative treatment alone, involving keeping the mare in a quiet stall. The foal is typically not separated from the mare because separation will induce additional and significant distress. However, in some instances foals may be at risk for injury from hemorrhaging mares that colic violently or stagger around the stall. Techniques to temporarily remove the foal to a safe area that still allows contact with the mare and does not induce stress for the mare should be explored. The question of when to intervene and replace lost blood volume with either whole blood or fluids is dictated by economics and clinical signs. Fluids and transfusions improve perfusion but may also increase blood pressure and potentially disrupt a formed clot. Similarly, a painful mare can disrupt a forming clot by rolling or falling violently, so the mare should be given pain relief in the form of flunixin meglumine (1.1 mg/kg, IV) and butorphanol (0.01 to 0.04 mg/kg, IV or IM). Providing sedation and analgesia in the form of α2-adrenergic agonists (detomidine, 0.004 to 0.02 mg/kg IV) or xylazine (0.2 to 0.8 mg/kg, IV) is also recommended. Aminocaproic acid (100 mg/kg loading dose followed by 50 mg/kg, IV, given twice daily) and tranexamic acid (10 mg/kg, IV) are reported antifibrinolytic agents and may be useful. Some reports suggest that treatment with formalin or the opioid antagonist naloxone (0.2 mg/kg, IV) may be helpful, but there is limited scientific evidence to support their use.
The prognosis for survival is dependent on clinical signs within the first 48 hours after foaling, the site of hemorrhage, and response to treatment. Mares that bleed directly into the abdomen generally have a poorer prognosis than those that bleed into the broad ligament or vaginal wall. A fully polymerized clot will have formed by 5 to 7 days after hemorrhage, but it is recommended that the mare not be moved for a further 5 to 7 days. The authors have seen mares that had no clinical signs of hemorrhage for the first 4 days after foaling suddenly begin to hemorrhage from a uterine artery rupture that presumably occurred at foaling and had been contained. It has been suggested that mares that have had a previous episode of hemorrhage are more likely to bleed again and that this is related to decreasing elasticity of the arterial walls in older mares.
Retained Fetal Membranes
Retained fetal membranes (RFM; see Chapter 171) may be the most common postpartum complication encountered in clinical practice, occurring in 2% to 10% of postpartum mares. It is generally accepted that membranes are retained if they have failed to pass by 3 hours after foaling, although, in the wild, mares have been reported to retain membranes for up to 2 days without showing ill effects and still produce a foal the following season. The incidence of RFM is increased with dystocia, prolonged gestation, hydrops conditions, cesarean delivery, in draft breeds, and in mares older than 15 years. The nongravid horn is the most commonly retained portion. The consequences of retained fetal membranes range from no effect to toxic metritis and endotoxemia with secondary laminitis and death.
The presence of placental material protruding from the vulva is not in itself a reliable diagnostic criterion because the placenta may be retained in its entirety or may be torn with just a portion remaining in the mare. Inspection of the placenta after parturition should always take place, with special attention paid to the horns and presence of any tears. It is useful to turn the membranes inside out and match the course of the blood vessels to determine whether an area is torn or if there is a portion missing or retained. It is not uncommon to discover retained membranes several days after foaling, when a mare develops a vaginal discharge. Occasionally, these mares show signs of endotoxin absorption. Ultrasonography of the uterus may be useful in these cases.
Oxytocin appears to be useful in any treatment plan. The protruding membranes should be tied in a knot to prevent the mare standing on and tearing them, and treatment with 10 to 20 IU oxytocin, given intravenously, hourly, is initiated after 3 hours of retention. This regimen alone is typically successful at inducing passage of the membranes. Use of manual traction remains controversial; however, the authors believe that if executed with due care and in conjunction with oxytocin therapy, this procedure can be very effective and cause no detrimental effects. This typically occurs in cases in which the membranes are ready to be passed and there is little or no interdigitation of microvilli left in the endometrium. If the RFM are still present after 8 hours and after repeated doses of 10 to 20 IU oxytocin, voluminous lavage and manual removal should be attempted. Forced extraction is contraindicated. If attempts at gentle manual removal fail, oxytocin treatment, along with broad-spectrum antimicrobials and nonsteroidal antiinflammatory drugs, is initiated and the mare revisited 24 hours later for repeated lavage and gentle manipulations. Intravenous calcium borogluconate (50 to 250 mL of a 20% solution) may also be useful in some mares. If the chorioallantois is intact, it can be distended by instillation of warm water (9 to 12 L) and secured to prevent escape of the fluid. This method appears to induce endogenous oxytocin release and separation of microvilli from endometrial crypts and can be effective within 5 to 30 minutes. Exogenous oxytocin treatment can be continued during this procedure.