Marc Kinsley, D.V.M.

Colic is an all too common problem in the equine world and there are multiple steps that we as veterinarians go through to diagnose the cause of discomfort.  A comprehensive physical examination including a rectal exam is usually the first step in diagnosis.  Rectal examination is generally followed by nasogastric intubation to check the horse for reflux, or build up of fluid in the stomach.  In a hospital setting, such as at Mid Atlantic, all colics have blood drawn for a complete blood count (CBC) and a serum biochemistry analysis.  So why do we choose to perform these clinical pathologic examinations and what do they tell us about a colicky horse?

A CBC allows us to measure the numbers of red blood cells, total protein and the number of different white blood cells.  The packed cell volume or PCV (the concentration of red blood cells) and total protein values allow us to monitor a horse’s hydration status.  A PCV of greater than 45% is often indicative that the horse is clinically dehydrated.  The red blood cell count and the other red cell parameters can help us as veterinarians diagnose anemia and determine if the anemia is chronic or acute in nature.  White blood cells are the body’s immune cells that protect the body from infection and aid in healing.  The white blood cell count measures the total white blood cells and the numbers of neutrophils, eosinophils, lymphocytes, monocytes, and platelets in the blood.  Leukopenia, or a decreased number of white blood cells, is often a feature of acute diseases of the gastrointestinal tract.  For example, in cases where intestine has lost its blood supply (surgical colics), the leukocyte count can fall to very low levels in the blood as the leukocytes attempt to protect the body from the compromised intestine.  Leukocytosis, or increased white blood cell count, can accompany acute, progressive, or chronic inflammation of the intestinal tract.  A blood smear is often made, and the way the white blood cells appear on the slide can often tell us if the cells look toxic, or if a large number of immature cells have been released from the bone marrow in response to decreasing numbers in the peripheral blood.  The information from a CBC aids in the diagnosis and treatment, and a chemistry panel assists us even further.

A standard chemistry panel can tell a veterinarian about a horse’s electrolytes, plasma proteins, kidney function, liver function, intestinal integrity, and allows us to assess muscle damage.  In the case of a colic, often times electrolytes may be lost into the gastrointestinal tract.  This loss, if great enough can place a horse at greater risk for complications if it needs to go under anesthesia.  Alkaline phosphatase is often measured and is found in the brush border of the intestinal wall.  In cases of increased intestinal wall damage, this enzyme leaks into the blood and increases in concentration.  Kidney values, such as creatinine and blood urea nitrogen may increase in colicking horses because of dehydration.  Acid base status can also be interpreted from a chemistry panel and can tell us about a horse’s perfusion. In many colics, poor perfusion leads the cells of the body to switch to anaerobic metabolism.  This type of metabolism provides energy to the cells to allow them to remain alive, but leads to the production of lactic acid.  Lactic acid increases in horses with surgical colic and can also place horses at increased risk while under anesthesia.

Clinical pathology aids in the diagnosis and treatment of colic disorders.  The determination if a horse needs surgery or medical therapy can be difficult and these simple blood tests are one more way to help distinguish the difference.