The weight of the pregnant uterus on the caudal epigastric and caudal superficial veins may restrict drainage of the area, and a severe plaque of ventral edema can extend from the udder to the xiphoid. Mares with a ventral hernia present with a similar plaque of inflammatory edema. Damage to the musculature by external trauma can also cause edema. Progressive enlargement of a rent in the abdominal wall causes pain that makes affected mares walk slowly; often they are reluctant to move at all. Discomfort is displayed when the caudal abdomen is palpated. The defect and/or hernial contents are usually difficult to palpate transabdominally due to the edema. Transrectal palpation of the defect is seldom possible because of the presence of the fetus and the large, dependent uterus. Transabdominal ultrasound permits visualization of any abdominal contents that may be herniated through the rent in the body wall. Tears may be difficult to distinguish from separation of the musculature by severe edema, and careful ultrasonographic evaluation is indicated.
Treatment of Abdominal Wall Hernias
Initial treatment of a suspected hernia should be directed toward stabilization of the mare through confinement to a small area and restricting exercise. External abdominal support in the form of a belly-band should be used to transfer abdominal weight to the vertebral column. Administration of laxatives and reduction of the bulk of the ration will prevent constipation. If the foal is viable and mature, parturition should be induced to decrease the risk of uterine blood vessel rupture or enlargement of the defect to the point where abdominal discomfort and weakness leads to recumbency. Induction of parturition with the use of cloprostenol (two doses of 250-500 μg, 30 minutes apart), or oxytocin (20 IU, repeated as needed, or 50 IU in a saline drip) has been effective in this author’s experience. Delivery must be assisted because the mare will be unable to mount an adequate abdominal press. Excessive exertion should be minimized to prevent any enlargement of the hernia. A cesarean section should be considered if the prognosis for the mare is poor, and the viability of the foal is of primary concern. Surgery is also indicated if incarceration of a piece of bowel is suspected. If the pregnancy is not sufficiently advanced to permit delivery of a viable foal then abdominal support and supportive care should be maintained until induction or surgery is feasible.
Transverse, oblique, and ventral hernias may not be well delineated prepartum but when the edema resolves after delivery the rents will become more evident. An abdominal support should be worn for 2 to 3 months until the edema resolves and a fibrous ring forms at the sight of the hernia. Surgical repair with propylene or plastic mesh has been successfully performed. Smaller defects may heal by second intention. Reproductive capacity postrepair is not known; however, constant supervision and assistance during parturition is necessary so that further damage does not occur. In cases where defects are unable to be repaired, future pregnancies are unwise. Embryo transfer or other new assisted reproduction technologies may be the best option.