It's nearly foaling season on the farm where I work, and a groom was telling me about a foal last year that died of bladder rupture on this farm.
Bladder rupture is a tear or leak in the urinary bladder that results in uroperitoneum.
Although bladder ruptures can occur in adult horses, usually from urinary tract obstruction, the vast majority of bladder ruptures occurs in foals. The rupture in foals usually occurs in the bladder itself, but also can occur in the urachus. The urachus, a structure in the fetus which lies between the tip of the bladder and the umbilical cord, allows the excretion of urine. This structure normally is closed at birth, and over several weeks contracts to a thick band of tissue. Most bladder ruptures in foals occur during parturition.