Tests or procedures used by your vet to determine what is wrong with your horse, in order to reach a diagnosis.

Cost: Under $100

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.


Abdominocentesis, Belly or Abdominal Tap

Cost: Under $100

These cost ranges are approximate and may vary from region to region.
Additional charges may also apply.


In a healthy horse a small amount of clear, pale yellowish fluid bathes all the abdominal organs. This fluid is secreted by the cells lining the abdomen and it is continuously produced and reabsorbed.

Abdominocentesis (aka belly tap) is the sampling and analysis of this fluid. The fluid reflects the state of the intestine and abdominal organs and is useful in understanding more about the condition of the intestine and organs.

It is a common test used in cases of abdominal pain (colic) or in any situation where abdominal disease is suspected. The results of the fluid analysis are interpreted in conjunction with the results of other diagnostics.

In a normal horse, there is only a small amount of fluid, about 50ml of free fluid in the abdomen. A site is selected down low and forward on a horse's belly, away from organs and where the fluid is likely to collect. The skin is clipped and surgically scrubbed to prevent infection. Using sterile technique, a needle is introduced into the abdomen. The needle tip enters the small pool of free fluid. Fluid drips out the needle and is captured in a tube for analysis.

In cases where the horse is fat or large, a regular hypodermic needle may not reach through the body wall into the abdomen. In this case, after injection of local anesthetic, a puncture is created in the skin with a blade and a long sterile, blunt stainless steel tube (teat cannula or bitch catheter) is pushed through the abdominal wall. The vet uses care not to penetrate abdominal organs or intestine.

Sometimes there is very little fluid or it can be hard to reach or collect for a variety of reasons. In this case, ultrasound may be used to identify pockets of fluid for collection.

The fluid collected is analyzed based on appearance, amount, total protein, and cell counts. Clear pale yellowish or amber fluid with a low protein level and cell count is generally an indication that the intestine is not severely damaged.

In contrast, blood tinged red-orange fluid or fluid containing feed material with high protein and blood cells is often indicative of damage or inflammation. Changes in fluid characteristics are helpful in determining the need for colic surgery, but are only one factor of many considered.

In extreme cases the fluid is filled with blood, feed or fecal material and may indicate that the intestine has been ruptured. In this case, euthanasia may be considered.

Why A Vet Chooses This Diagnostic


Diagnoses Your Vet May Consider

This test could rule out or confirm any of the following diagnoses.

Very Common
Less Common
more diagnoses
Abdominocentesis is a quick, relatively noninvasive way to assess the health of the equine intestine and abdominal organs. It is often used to help determine the severity of the disease process and is helpful in determining the proper course of action in colic cases. The incidence of side effects is low. This is considered a safe and routine procedure.


Fluid can remain relatively normal in cases of severe intestinal obstruction for a variety of reasons. The fluid changes slowly in cases not involving strangulation of the intestine.

Rarely, there can be a pool of normal fluid and a pool of more abnormal fluid in the same abdomen, separated by an organ or part of the intestine. The sampling of the clean fluid can mislead the clinician into thinking the disease process is less severe than it is.

Fluid can be difficult to collect in some cases. This is especially true in horses with thick or fat abdominal walls. Ultrasound is extremely helpful in localizing fluid for sampling.

It is easy to puncture the intestine. In this case, greenish fluid with bits of feed is sampled. This usually indicates that another sample needs to be collected.

further reading & resources

Related References:

Hanson RR, Nixon AJ, Gronwall R, et.al. Evaluation of peritoneal fluid following intestinal resection & anastamosis in horses. Am J Vet Res 1992;53(2);216-21.

Author: Doug Thal DVM Dipl. ABVP