Rectum: biopsy in Horses (Equis) | Vetlexicon
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Rectum: biopsy

ISSN 2398-2977

Contributor(s) :


  • Histopathological examination of tissues from the large intestine can help in the diagnosis of chronic inflammatory, infiltrative or neoplastic conditions.
  • Rectal mucosal biopsies may be diagnostic in up to 30-50% of chronic enteropathy cases.
  • Negative findings do not rule out the possibility of pathology in the rest of the gastrointestinal tract and should be interpreted with caution.



  • Easy and simple to collect.
  • Minimal complications if performed correctly.
  • Minimal equipment required.
  • Low cost.


  • The pathological process has to be extensive enough to affect the rectum.
  • Up to 33-50% of rectal biopsies are positive in horses with clinical signs of intestinal disease.

Alternative techniques

Time required



  • Sampling: 5 min.

Decision taking

Criteria for choosing test

Risk assessment

  • Minimal compared to risks of general anesthesia (laparotomy Abdomen: laparotomy) if the procedure is performed correctly.



Veterinarian expertise

  • Minimal.
  • Familiarity with biopsy techniques will expedite comfort with obtaining rectal biopsies. 

Nursing expertise

  • Minimal experience with properly handling specimens.

Other involvement

  • Histopathologist.

Materials required

Minimum equipment

  • Biopsy punch: many types are available but most clinicians use an endometrial/uterine biopsy punch Endometrium: biopsy.
  • Important that it is well maintained and has sharp edges otherwise tearing of the mucosa may occur.

Minimum consumables

  • Rectal gloves.
  • Lubricant.
  • 4% formalin saline.
  • Tail bandage.



Site preparation


  • Rectum dorsolaterally.


  • Restrain horse.
  • Bandage tail.
  • Remove feces from rectum.

Other preparation

  • May provide local anesthesia with carbocaine carbocaine or lidocaine Lidocaine.
  • May perform a caudal epidural, though this is generally unnecessary to complete this procedure and is patient dependant.



Core procedure

Step 1 - Introduce biopsy punch 

  • Place the end of the uterine biopsy punch into the rectum followed immediately by the left/right hand.
  • Gently guide the end of the punch laterally onto the rectal mucosa, approximately a hand's-length in from the anal sphincter.

Do not take biopsy too far cranially - always from intra-pelvic rectum to avoid the risk of rectal tearing and communication with the peritoneal cavity.

Step 2 - Take biopsy

  • Gently pinch a fold of rectal mucosa between 2 fingers at approximately 1-2 or 10-11 o'clock position.
  • Introduce fold into jaws of punch.
  • Close the biopsy jaws tightly over a small piece.


Step 1 - Remove punch and specimen

  •  Gently withdraw punch and hand from rectum, keeping the biopsy punch jaws closed.

A slight twisting movement may be required as the punch is removed to loosen the biopsy specimen from its attachment.

Step 2 - Fix specimen 

  • Release sample from biopsy punch and check.
  • Place into fixative (4% formalin saline).


Immediate Aftercare


  • Monitor for straining to defecate, decreased appetite, increased heart rate, increased temperature, or changes to the mucous membranes (toxic line, delayed capillary refill time, increased redness).

General Care

  • Monitor passage of feces for evidence of rectal bleeding up to 48 h post-biopsy.


  • Non-steroidal anti-inflammatory such as flunixin meglumine Flunixin meglumine may be administered to decrease pain and inflammation for 3 days.


  • Generally unnecessary unless changes to the physical examination and/or complete blood chemistry.

Other medication

  • Laxatives may be needed if straining to defecate or feces are too hard.

Potential complications

  • Rectal hemorrhage may be a problem but it is usually self-limiting.

Do not take biopsy too far cranially - always take the sample from intra-pelvic rectum. Failure to do so may → creation of a rectal tear that communicates with the peritoneal cavity with potentially catastrophic consequences Rectum: tear.


Reasons for treatment failure

  • Negative biopsy results may be related to poor sampling or lack of rectal infiltration by disease process and should be interpreted with caution.


  • Depends upon individual disease entity.
  • Conditions that may be detected using rectal biopsy include:
    • Acute/chronic granulomatous or eosinophilic proctitis.
    • Cyathostominosis.
    • Diffuse intestinal lymphosarcoma.
  • The results of rectal biopsy should be taken in combination with the results of clinical and other diagnostic tests.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Stewart H L, Engiles J B, Stefanovski D & Southwood L (2018) Clinical and intestinal histologic features of horses treated for recurrent colic: 66 cases (2006-2015). JAVMA 252 (10), 1279-1288 PubMed.
  • Schumacher J, Edwards J F & Cohen N D (2000) Chronic idiopathic inflammatory bowel diseases of the horse. J Vet Intern Med 14 (3), 258-265 PubMed.
  • Lindberg R, Nygren A & Persson S G B (1996) Rectal biopsy diagnosis in horses with clinical signs of intestinal disorders: a retrospective study of 116 cases. Equine Vet J 28 (4), 275-284 PubMed.
  • Ricketts S W (1996) Rectal biopsy - a piece of the diagnostic jigsaw puzzle. Equine Vet J 28 (4), 254-255 PubMed.