How to Manage Hydrops Allantois/Hydrops Amnion in a Mare

Hydrops conditions of the placenta in the mare are uncommon, with hydrops allantois being reported more frequently than hydrops amnion. The condition in the mare usually develops during the last trimester of pregnancy and is characterized by the excessive accumulation of allantoic (hydrops allantois) or amnionic fluid (hydrops amnion). The sequelae of unnoticed or untreated hydrops allantois/ amnion can be significant, including abdominal wall hernias, prepubic tendon rupture, and cardiovascular shock associated with unattended foaling and dystocia The condition is often detected by the horse owner as a sudden onset of abdominal enlargement (over a period of a few weeks), ventral edema, varying degrees of colic, lethargy, anorexia, tachycardia, and, on occasion, dyspnea associated with intra-abdominal hypertension (Fig. 1). Differential diagnoses include twins, other causes of colic, and causes of ventral edema. Definitive diagnosis requires a trans-rectal examination of the reproductive tract and transabdominal sonogram to detect abnormally abundant fetal fluids. The allantoic fluid volume in mares with hydrops allantois can range from 110 to 230 L, whereas a normal volume at term ranges from 8 to 18 L. Rectal examination will reveal a large, fluidfilled uterus of varying tightness with the dorsal Fig. 1. Mare with hydrops allantois. Note the pendulous “pearshaped” abdomen.