Rupture of the urinary bladder can occur sporadically in foals during the birth process. It is postulated that the rupture of the bladder wall is caused by increased abdominal pressure as the foal passes through the dam's birth canal. Others have suggested that it may be due to a developmental defect. Some studies have shown a higher incidence in male foals but it also occurs in females. Because the bladder has a hole in it, urine leaks from the bladder into the abdominal cavity. As the urine accumulates in the abdomen, clinical signs of disease become apparent at about 3 to 4 days of age. The bladder can also leak as a result of an infection of the umbilical structures of the foal. Clinical signs from this type of leakage usually occur at a later age – 5 to 8 days of life.
What to Watch For
Sometimes it is difficult to distinguish whether the foal is standing to urinate or defecate. When a foal postures to urinate, he flattens out his back and squats. To defecate he arches his back.
The distention of the abdomen is also sometimes confused with bloat. In the ruptured bladder the foal is essentially urinating into his abdomen. As the urine accumulates the abdomen enlarges. If you were to ballot or push on the foal's side you may be able to detect a wave of fluid bouncing off the abdominal wall.
Urine is composed of a different electrolyte balance than normal blood. Urine is higher in potassium and lower than sodium and chloride than blood. It is also very high in a substance called creatinine, which is the body's waste product. When urine spills into the abdomen, the electrolytes equilibrate back into the blood. This dilutes the normal blood's sodium and chloride while it increases the blood's potassium levels. This can be very dangerous to the foal because high blood potassium can cause the heart to beat irregularly. Creatinine is a large molecule that cannot cross into the blood; instead it remains high in the abdomen.
Several other diseases can mimic the depression and colic that may be seen in foals with ruptured bladders. The depression can be seen in foals with septicemia or hypoxic ischemic encephalopathy (HIE). The timing may be a clue to helping you with the diagnosis. Sepsis and HIE will usually occur after birth while the signs of the ruptured bladder are progressive and may not be noted until 3 days of age. Other causes of colic need to be ruled out as well.
Clinical signs of straining to urinate and a distended abdomen will be suggestive of urine in the peritoneal cavity, or uroperitoneum, but several diagnostic tests will aid in a positive diagnosis of a ruptured bladder. Blood work will show decreased sodium and chloride levels and an elevated potassium. Usually there is also an elevated blood creatinine if the foal is dehydrated. Ultrasound of the abdomen will reveal the presence of a large amount of fluid. Visualization of the bladder with the ultrasound may be difficult because it is small. Your veterinarian may take a small sample of the abdominal fluid with a needle and analyze it for creatinine. If the creatinine in the abdomen is higher than the creatinine in the blood it is a confirmed ruptured bladder.
If left untreated, the foal will die. Surgical repair is the best method of treatment but the deranged electrolytes in the foal will make it a high risk for cardiac arrest if it is not corrected before surgery. Correction of the electrolytes involves specific fluid therapy and possible abdominal drainage. After surgery the foal may have a urinary catheter placed for a few days to allow the bladder closure to heal.
Early recognition is important for the successful treatment of a ruptured bladder. You should observe your foal's everyday behavior. Is he producing urine when he postures? Is he trying to urinate or defecate? Is his abdomen becoming large? If the abdomen appears to be increasing in size, use a tape measure several times a day. Call your veterinarian if the foal is not acting normally.
After surgery the foal may be sent home for nursing care. Prognosis is good if the problem is caught early and the foal is stabilized before surgery. Postoperative care of the foal will be include stall rest for 14 days with limited walking until the incision has healed. Antibiotic administration usually continues for seven days. Be sure to administer it for the amount of time recommended, even if he appears to be better.