Rectal Examination of the Horse

Repeated rectal examinations are the cornerstone of colic diagnosis, as many large intestinal conditions can be definitively diagnosed by this method alone. It should be performed in every horse with abdominal pain, pyrexia of unknown origin,chronic diarrhea and weight loss. The rectal temperature must be taken prior to the examination. Rectal examination will not be possible in foals or very small ponies. Fractious horses should be sedated with Xylazine which provides short term analgesia and sedation.It is important to restrain the horse. This may be done in the stocks if they are available but horses of a good nature may be examined over the stable door with the use of hobbles or hay bales. The amount and consistency of the feces in the rectum should be noted before the start of the examination. The process should be conducted in a consistent and systematic manner to avoid missing lesions. Care is required as there is a risk of irritation or rupture of the rectum during the examination. It is important to restrain the horse. The veterinarian should wear a plastic rectal glove with adequate lubrication before entering the rectum. The horse may strain and the veterinarian may feel peristaltic waves. It is important to be patient and not to use force to move the arm forward as this will increase the risk of a rectal tear. The feces must be evacuated from the rectum prior to the examination. If the horse continues to strain, lidocaine can be mixed with the lubricant to reduce th straining and provide analgesia. Alternatively, a spasmolytic may be administered. The examination should start with the pelvis structures and then move to the left cranial abdomen, proceeding clockwise.

Normal Intraabdominal Structures Palpable in the Horse

• Bladder
• Female reproductive tract in the mare
• Inguinal canals and Urethra of the stallion
• Caudal border of the spleen
• Nephrosplenic ligament
• Caudal pole of the left kidney
• Mesenteric root
• Ventral cecal tenia (no tension should be palpable)
• Cecal base ( should be empty in the normal horse)
• Small colon containing fecal balls
• Pelvic flexure

When examining the organs per rectum, it is important that the veterinarian notes the position, size, consistency, mobility, distension due to gas or ingesta, evidence of edema and tight mesenteric bands.

Staring in the pelvic region, the inguinal canals of the stallion can be palpated both sides of the pelvic opening, at the level of the pelvic brim. A full bladder can obscure the examination and so encouraging the horse to urinate or catheterisation can be beneficial. The veterinarians arm is carefully moved forward to the left dorsal quadrant and is able to palpate the caudal border of the spleen, left kidney and the nephrosplenic ligament connecting them. Moving over to the dorsal midline, the pulsing aorta can be felt attached to the dorsal body wall, below the spine. The mesenteric root runs dorsoventrally down the midline of the abdomen. The base of the caecum can be palpated in the right dorsal quadrant. The caecum is normally not full and so the veterinarian should also be able to palpate relaxed cacal taenia running dorsoventrally. The pelvic flexure can be palpated ventrally at the level of the pelic brim,to the left of the midline. The smooth and narrow left dorsal colon and the longitudinal bands of the wide left ventral colon can be palpated, extending from the pelvic flexure. The small intestine is not palpable except for the ileum in some horses or unless there is an abnormality. The small colon is easily distinguishable by the distinct fecal balls within its lumen.

References

• Edwards B. (2009) Rectal Examination, Equine Gastroenterology courtesy of the University of Liverpool, pp 55-57
• Meuller E, Moore J. N (2008) Classification and Pathophysiology of Colic, Gastrointestinal Emergencies and Other Causes of Colic, in Equine Emergencies- Treatments and Procedures, 3rd Edition, Eds Orsini J. A, Divers T.J, Saunders Elsevier, pp 108-110
• Rose R.J, Hodgson D.R (2000) Examination of the Alimentary Tract, Alimentary Tract, Manual of Equine Practice, 2nd Edition, Saunders Elsevier, pp 274-283
• Archer D. (2004) Decision Making in the management of the colicky horse, In Practice