Beyond retained fetal membranes: Managing conditions affecting the postpartum mare

Complications in the early postpartum period are a common and challenging problem for the equine clinician. This presentation reviews some of the specific problems encountered in the postpartum mare.

Periparturient haemorrhage

The most frequent cause of haemorrhage during parturition is rupture of the middle uterine artery and the risks of rupture are greater in older mares especially those that have had multiple foals. The majority of bleeds are contained within the broad ligament resulting in a haematoma however the bleed can occur directly into the abdominal cavity or into the uterus. Broad ligament, uterine or pelvic wall haematomas often result in colic due to the stretching of the tissues. If an artery ruptures directly into the peritoneal cavity the mare may not be painful but the haemorrhage may be more profuse and rapidly fatal.

In the acute phase of haemorrhage haematology may show an increase, decrease, or no change in packed cell volume (PCV) due to splenic contraction, hypoproteinemia and hyperlactatemia would be suggestive of blood loss in a horse. If the mare survives the acute phase, a drop in PCV is usually observed over the following days before a regenerative red cell response can be made. Transabdominal ultrasound can be performed to detect free fluid in the abdomen and abdominocentesis can be obtained to confirm an elevated red cell count indicative of haemoabdomen. In cases with broad ligament haematoma the peritoneal fluid protein levels can be significantly elevated (up to 50 g/l) with normal white cell count.

Treatment is challenging and often controversial. If the mare survives the initial haemorrhage, it is likely that a clot has formed. In all cases, keeping the mare quiet is paramount to her survival. If the mare is actively haemorrhaging the approach is governed by the facilities available and the economics of the particular case. In some instances, an extreme hypotensive state may actually offer the best chance for survival, whereas in others an attempt to restore intravascular pressures and circulatory volume with iv fluid therapy could be indicated. The need to support cardiac output and ensure oxygen delivery must be balanced against the prospect of the increased arterial pressure promoting further haemorrhage. Conservatively mild sedation (alpha-2 agonist), pain relief with butorphanol and/or flunixin meglumine are recommended. Prophylactic broad-spectrum antibiotic coverage is warranted and low dose (10 iu) oxytocin therapy may be useful to promote uterine involution.

Aminocaproic or tranexamic acid may be beneficial; in horses an extrapolated dose of 10mg/kg tranexamic acid is given by slow i/v injection up to three times in the first 24 hours depending on the severity of bleeding. Fletcher and co-workers (2013) showed that the minimum concentrations of aminocaproic and tranexamic acid required to inhibit fibrinolysis in horses were approximately 1/20 those required in humans. Although controversial, formalin (16 ml of 10% buffered formalin diluted in 45 ml of 0.9% saline solution and administered by slow i/v injection has also been used to treat uncontrolled haemorrhage in horses and appears to have short term safety (Moreno et al. 2021).

Metritis

Incidence of metritis is low but increases with birth trauma and retained fetal membranes. It usually presents within 2-4 days postpartum and is often associated with a pronounced neutropenia. Inflammation of the uterine wall permits bacteria and toxins to enter the systemic circulation, resulting in bacteraemia and endotoxaemia. Any postpartum mare with fever and anorexia should be suspected of having metritis. A large volume of toxic, red-brown, watery fluid may accumulate within the postpartum uterus before any obvious vaginal discharge becomes apparent.

Treatment should include broad-spectrum antibiotics, anti-inflammatory drugs and intravenous fluids if indicated. A combination of procaine penicillin and gentamicin are widely used to provide broad-spectrum systemic coverage. Anti-endotoxic doses of flunixin meglumine (0.25 mg/kg bodyweight three times a day) should be considered as a minimum; 10-20 iu oxytocin every 4-6 hours will promote uterine clearance and involution. Daily or twice daily large volume uterine lavages with 0.9 per cent saline solution are a routine part of managing mares with metritis. Homemade (non-sterile) saline can be used in the post-foaling mare by mixing 90 g of table salt with 10 litres of tap water. The lavage is repeated until the recovered fluids are free from gross contamination.

Uterine laceration

Uterine lacerations occur most frequently after dystocia but can occur in mares that foal normally. The most common sites of laceration are the ventral and dorsal uterine body and the tip of the pregnant horn. In the early stages there may be no obvious outward clinical signs. Subsequent signs are dependent upon the degree of contamination of the uterus and abdominal cavity. If peritonitis develops the mare becomes increasingly ill over 24-72 hours with fever, inappetence, reduced gut motility and abdominal pain. Abdominocentesis will reveal signs consistent with septic peritonitis and changes in haematological and biochemical parameters may also be present. One should be aware that peritonitis due traumatised and devitalised bowel is a major differential.

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