Horses with signs of colic can be grouped into one of three categories:
- horses which are resolved after medical management at the farm;
- horses which are resolved after more intensive medical management at a referral facility; and,
- horses which are resolved after performing emergency abdominal surgery.
In a study of 1,929 equine ambulatory calls made during two years, 7.6% (147 out of 1,929) of these calls were to treat horses with signs of colic, and only one horse required emergency abdominal surgery, suggesting that the great majority of colicky horses resolve with medical management.
Veterinarians assign horses into one of these three categories after reviewing the pertinent aspects: a thorough history, a complete physical examination, and any laboratory data deemed significant. A complete physical examination includes evaluation of the horse's clinical signs (e.g., depression, abdominal distension, sweating), the cardiovascular system (e.g., heart rate, mucous membrane color, capillary refill time), reflux from the stomach after passing the nasogastric tube (e.g., fluid volume, color, smell), the quality and duration of pain relief by analgesics (e.g., flunixin meglumine, butorphanol), and findings of examination per rectum. Although it is not necessary to perform all of the items listed when evaluating horses, veterinarians gather information from these areas to formulate a diagnosis.
Findings of examination per rectum have been suggested to be the most important aspect of the physical examination in a horse with signs of colic, therefore evaluation of the gastrointestinal tract per rectum is usually performed on all horses with signs of colic. Performing an examination per rectum is not without risk, and should only be performed by an equine veterinarian. Rupture of the equine rectum is a life-threatening complication, and a high percentage of horses with rectal tears die or are euthanized. In spite of risks, this procedure is extremely valuable because it provides important information regarding the need for surgical intervention or conservative management.
Technique
When performing an examination per rectum, the risks of injury to the patient or examiner can be reduced by using proper technique. By positioning the horse in a stall doorway or in a set of palpation stocks, movement during the procedure can be minimized. The procedure can often be performed in the quiet patient with no more than a twitch on the nose. In anxious or painful horses, it might be necessary to provide sedation, a topical anesthetic for the rectum, or epidural anesthesia.
The location of the intestines are variable due to their mobility; however, the approximate location of intestines and the flow of ingesta can be followed in Figures 1-3. It is not possible to evaluate the entire gastrointestinal tract during examination per rectum, given the size of the abdominal cavity. Approximately 40% of the abdominal cavity can be evaluated in the adult horse, using this technique. With this in mind, only the structures that can be identified during examination per rectum will be discussed.
Examination Per Rectum: Left Side of Abdomen
The aorta can be felt at the 12 o'clock position on the roof of the pelvis and on the dorsal aspect of the abdomen. The aorta divides the abdomen into left and right halves, and directs the veterinarian's hand into the center of the abdomen. The caudal pole of the kidney (Figure 4) can be identified just to the left of the aorta at an arm's length from the anal sphincter. A prominent ligament (nephrosplenic ligament) can be felt as it connects the ventral aspect of the kidney to the dorsomedial aspect of the spleen (Figure 4). The ascending colon can move from its normal ventral position and become abnormally entrapped in the potential space created by this ligament (Figure 4). Having identified the spleen, its caudal border can be palpated in a vertical position against the left body wall.
The left ascending colon can be identified just ventral to the spleen against the left body wall (Figures 4 and 5). The ascending colon is a "horseshoe-shaped" piece of large intestine that has dorsal and ventral segments (Figure 5). During examination per rectum, the dorsal (without bands and sacculation) and ventral (with bands and sacculation) component can be distinguished by the presence or absence of broad fibrous bands and sacculation (Figure 5). Displacements, torsions, and strangulations of the ascending colon are the most common findings identified during exploratory celiotomy in the horse with signs of colic. The pelvic flexure connects the left ventral colon to the left dorsal colon (Figures 3 and 5), and often can be identified in the lower caudal aspect of the left side of the abdomen. The pelvic flexure is a narrowed portion of the ascending colon and a common problem area in horses with signs of colic due to impacted ingesta. Impactions with ingesta are a type of colic that can often be resolved with medical management.
The small intestine is usually collapsed and therefore not palpable in the normal horse (Figures 1-3). Loops of small intestine that are easily identified during examination per rectum alert veterinarians that a given horse might require surgical intervention. The mesenteric sheet of the jejunum (the tissue that suspends the small intestine from lumbar region of the dorsal body wall) is quite long and enables the small intestine to be highly mobile (Figure 3). The majority of the small intestine is usually contained within the center of the "horseshoe-shaped" ascending colon, and towards the left hand side of the horse's abdomen (Figures 1-3). The descending (small) colon can be found in several locations in the dorsal aspect of the caudal left and right abdomen (Figures 1-3), and is identified by the presence of formed fecal balls and a prominent ventral band. When listening for intestinal sounds with a stethoscope in the left flank, you hear sounds from the small intestine in the upper quadrant, and colonic sounds (left ascending colon) in the lower quadrant.
Examination Per Rectum: Right Side Of Abdomen
Using the aorta to identify the center of the abdomen, the stalk (mesenteric root) that suspends the small intestine can be identified as a taut structure just to the right of center at an arm's length from the anal sphincter (Figure 3-D). At mid-arm's length from the anal sphincter, the base of the cecum can be identified and is firmly attached to the right dorsal aspect of the body wall (Figures 2-5). In the normal horse it is not possible to distinguish the ileum (the terminal end of the small intestine) as it empties into the medial (left side) aspect of the cecum (Figure 3-D), although this might be abnormally distended in the horse with signs of colic. The medial cecal band can be identified on the left side of the body of the cecum and directs the veterinarian's hand from the right side of the abdomen downward and towards the apex of the cecum on the midline of the abdomen (Figures 3 and 5). In the normal horse, the cecal band and the ventral band of the ascending colon are the only bands that can be easily identified during examination per rectum.
Although the inguinal rings can be difficult to find in the normal horse, they can be identified at the 4 and 8 o'clock position just in front of the floor of the pelvis. These structures can entrap small intestine in the intact male. When listening for intestinal sounds with a stethoscope in the right flank, one hears sounds from the base of the cecum in the upper quadrant, and colonic sounds (right ascending colon) in the lower quadrant.
Although findings of examination per rectum might be the most important part of a physical examination of a horse with signs of colic, identifying a specific cause during examination per rectum is not essential for determining the necessity of surgery. Significant abnormal findings identified during examination per rectum that indicate surgery include distended loops of small intestine, bands of the large intestine in abnormal locations, small intestine entrapped within the inguinal canal, and entrapment of the ascending colon over the nephrosplenic ligament.
Studies on colic indicate that assessment of individual factors alone cannot accurately determine the prognosis of horses with signs of colic. An accurate diagnosis and prognosis are formulated by assimilating the findings of an examination per rectum in combination with a thorough history, a complete physical examination, and pertinent laboratory data. Horse owners need to cooperate with their veterinarians when decisions have been made regarding the severity of horses with signs of colic and the need for referral. It is favorable to refer horses with mild signs of colic and abnormal findings on examination per rectum early in the course of the disease. Unwanted delays in treatment because of transportation requirements would be eliminated and therefore increase the likelihood of a successful surgical outcome.
