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

ISSN 2398-2977


  • Endometrial disease is common in the brood mare and the detailed histologic picture revealed by biopsy in association with other reproductive examination techniques can lead to a more accurate diagnosis and prognosis.



  • Allows detailed histological appraisal of the endometrium.


Confirm non-pregnancy prior to biopsy.

Technical problems

  • The correct sampling technique is important.
  • Obtaining a poor sample (too small or tissue crushed).

Alternative techniques

Time required


  • 15 min.


  • 10 min.

Decision taking

Criteria for choosing test

Risk assessment



Veterinarian expertise

  • Knowledge of how to undertake the procedure.

Nursing expertise

  • Not necessary, however a trained and knowledgeable assistant facilitates the procedure.

Other involvement

  • Owner/agent permission.

Materials required

Minimum equipment

  • Cotton wool +/- paper towel.
  • Disinfectant, preferably povidone-iodine surgical scrub Povidone-iodine.
  • Clean water in a container.
  • Obstetrical lubricant.
  • Per rectum palpation gloves.
  • Jackson equine uterine biopsy forceps (50-62 cm long; basket 2-4 mm by 15-28 mm).
  • Labeled containers with appropriate fixative (Bouins 10% buffered formal saline (BFS); modified Davidson's fluid (mDF)).
  • Needle/forceps to remove the sample from the basket.
  • Means of identifying the mare, eg microchip scanner/camera/passport, and documenting the findings (pen and paper/computer).

Ideal equipment

  • Jackson equine uterine biopsy forceps.

Minimum consumables

  • Cotton wool/paper towel for cleaning and drying the perineum.
  • Disinfectant: povidone-iodine scrub Povidone-iodine.
  • Per rectum palpation gloves.
  • Obstetrical lubricant.
  • Fixative within containers - approximately 50 ml.
  • Sterile hypodermic needle (such as 1 mm (20 g) diameter 25 mm (1 inch) long), or 'rat tooth' forceps (to remove the sample from the biopsy forceps).

Other requirements



  • Sedatives Anesthesia: standing chemical restraint - alpha-2 adrenoceptor agonists +/- opioids as necessary: depending on facilities, handlers, and horse demeanor.
  • Uncommonly, if additional chemical restraint is necessary, a caudal epidural Anesthesia: epidural may be performed. Caution with the use and/or volume of a blocking agent (lidocaine Lidocaine, mepivacaine Mepivacaine, etc) and the loss of pelvic limb function.
  • Ensure up to date tetanus prophylaxis Tetanus toxoid.
  • A dose of flunixin meglumine Flunixin meglumine may be given for pain and inflammation.

Site preparation

Other preparation

  • Ensure owner/agent permission.
  • Laboratory with appropriate histopathology expertise, sample transport preparation, documentation.




Step 1 - Preparation

  • Appropriate identification of the mare.
  • Appropriate restraint Restraint methods.
  • Bandage tailTail: bandageand support to one sideRestraint: tail tie.
  • Per rectum palpation Urogenital: rectal palpation and ultrasonography of the reproductive tract Ultrasonography: reproductive tract - female:
    • Remove feces.
    • Assess for pathology: uterine fluid, hyperechogenic uterine wall, etc.
    • Assess the stage of the estrous cycle Female: reproductive cycle - normal by matching ovarian findings with those of the season, uterine edema and cervical relaxation.
    • Ensure the mare is not pregnant, nor bred recently.
    • Record the information.
  • Clean the perineum - 'clean hand/dirty hand' technique.
  • Dry the perineum.
  • Ensure the biopsy equipment is prepared and ready for use:
    • Sterile/aseptic lubricant.
    • Sterile/aseptic arm length glove.
    • Sterile/aseptic Jackson equine uterine biopsy forceps.
    • Receptacles with fixative ready and open.
    • Needle/forceps for removing the sample from the Jackson forceps.
  • Mid-diestrus is the preferable time for biopsy; administer PGF2a after the sample has been collected.

Step 2 - Introducing the Jackson uterine forceps

  • If necessary/pertinent, obtain a uterine mucosal swab (double guarded) for microbiological and cytological assessment Endometrium: bacteriology. This is considered to be part of a BSE.
  • Grasp the Jackson forceps within an arm length gloved hand.
  • Lubricate the hand and lower arm.
  • Gently introduce the forceps into the caudal reproductive tract via the vulva within the gloved hand.
  • Locate the cervix at the cranial vagina.
  • Introduce the index finger into the cervix through the external os.
  • Pass the closed jaws of the Jackson forceps through the cervix using the index finger as a guide.
  • Slide the Jackson forceps into the body of the uterus.
  • Remove the gloved arm from the caudal reproductive tract.

Core procedure

Step 1 - Obtain the biopsy specimen

  • Introduce the gloved hand per rectum, relubricated as necessary.
  • Guide the jaws of the Jackson forceps to an appropriate position for taking the biopsy, using both hands - one per rectum and the other on the handle of the Jackson forceps. Typically the biopsy is taken at the junction of the uterine body and a uterine horn.
  • Once the forceps 'basket' (jaws) is (are) in the correct position, open up the jaws of the forceps.
  • Rotate the forceps 90° so that the jaws are parallel to the ground.
  • Gently place the superficial mucosa/fold of the uterus into the jaws of the forceps by pressing down with the hand in the rectum.
Do not press too hard, at it is possible to take a 'full thickness' (perforating) sample. But, press firmly enough to obtain a good sample of the mucosa.
  • Close the jaws of the Jackson forceps.
  • Release the pressure from the hand in the rectum.
  • Remove the Jackson forceps from the uterus with the biopsy sample within the jaws. A sharp pull might be necessary to facilitate the sample detachment.
  • Remove the hand from the rectum.
  • Typically one sample (representing about 0.1% of the endometrium) is sufficient to represent diffuse changes of the endometrium.
  • More samples may be necessary depending on other examination (ultrasonography, hysteroscopy) findings.

Step 2 - Processing the biopsy sample for histopathological assessment

  • Remove the sample from the opened jaws of the Jackson forceps using either a sterile hypodermic needle, or gently with 'rat tooth' forceps.
  • Place the sample directly into a labeled container with fixative - 10% BFS, Bouins, mDF:
    • There are some suggestions that the sample should be laid out on a piece of cardboard, and this should be placed in the fixative.
    • If placed in Bouins, the sample should be replaced in either alcohol (70%) or 10% BVS after 24 h.
  • The sample should be sent to the laboratory with the appropriate history and documentation.

Step 3 - Sample process for microbiological assessment

  • The jaws of the forceps can be swabbed for laboratory microbiological assessment - bacterial/fungus Endometrium: bacteriology.
  • A sterile sample of the tissue can be placed in a small amount (enough to keep the sample moist only) of sterile isotonic crystalloid (0.9% NaCl or Hartmann's solution) and submitted for laboratory assessment: smear cytology Endometrium: cytology and culture for microorganisms - bacteria/fungi.


Step 1 - Interpretation of biopsy results

  • The histopathological status of the endometrium is typically classified according to the following criteria:
    • Four grades: 1-4 or I, IIa, IIb, III (the grades are based on endometrial changes):
      • Estimation of the stage of the estrous cycle based on histopathological findings.
      • Distribution of lesions: widespread or diffuse, anatomial, eg periglandular, and frequency.
      • Inflammatory cell changes: acute (PMN) and chronic (lymphocytes and macrophages).
      • Severity of lesions: small, moderate or large.
      • Periglandular fibrosis (chronic irreversible and degenerative change) and 'glandular nesting'.
  • The grading or score indicates the prognosis of the mare becoming pregnant, and maintaining the pregnancy to term.
  • Theriogenologist interpretation (epicrisis) of the pathological report (which includes the history and clinical findings of the reproductive examination) should be sought to formulate a plan for the particular mare.
It is important to note that biopsy grades might alter with time and treatment, not necessarily worsening.


Immediate Aftercare


  • Monitor mare for 12-24 h for bleeding from vulva (rare).


  • Flunixin meglumine Flunixin meglumine may be given prior to and/or after the procedure as mild discomfort and inflammation may occur.

Antimicrobial therapy

Other medication

  • If the biopsy has been taken in diestrus, it is advisable to administer PGF2a to lyse the CL.

Special precautions

  • Ensure the mare is not pregnant at the time of biopsy.
  • Pregnancy is a possible outcome, especially if the mare is mated in estrus and prior to obtaining the (later estrus or metestrus) biopsy specimen.

Potential complications

Long term Aftercare

Follow up

  • Depends on results of the examination/assessment.



Reasons for treatment failure

  • Incorrect biopsy instrument placement:
    • Cervix: easy to recognize because no glands in tissue.
    • Bladder.
  • Pregnant mare.
  • Poor sample (not enough tissue or too much damage to tissue obtained).


  • Comparison of two biopsy samples taken before and after treatment (6 weeks) is very useful.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schöniger S & Schoon H A (2020) The healthy and diseased equine endometrium: a review of morphological features and molecular analyses. Animals (Basel) 10 (4), 625 PubMed. 
  • Linton J K & Sertich P L (2016) The impact of low-volume uterine lavage on endometrial biopsy classification. Theriogenology 86 (4), 1004-1007 PubMed. 
  • Buczkowska J, Kozdrowski R, Nowak M & Sikora M (2016) Relationship between uterine biopsy score, endometrial infection and inflammation in the mare. Tierarztl Prax Ausg G Grosstiere Nutztiere 44 (3), 158-163 PubMed. 
  • Snider T A, Sepoy C & Holyoak G R (2011) Equine endometrial biopsy reviewed: observation, interpretation and application of histopathologic data. Theriogenology 75 (9), 1567-1581 PubMed.
  • Ricketts S W & Alonso S (1991) Assessment of the breeding prognosis of mares using paired endometrial biopsy technique. Equine Vet J 23 (3), 185-188 PubMed.
  • Van Camp S D (1988) Endometrial biopsy of the mare. A review and update. Vet Clin North Am Equine Pract (2), 229-245 PubMed.
  • Ricketts S W, Rossdale P D & Samuel C A (1978) Endometrial biopsy studies of mares with contagious equine metritis 1977. Equine Vet J 10 (3), 160-166 PubMed.

Other sources of information

  • Schnobrich (2018) Disorders of the Reproductive Tract. In: Equine Internal Medicine. Eds: Reed S M, Bayly W M & Sellon D C. 4th edn. Elsevier, USA. pp 1235-1252.
  • Kenney R M & Doig P A (1986) Equine Endometrial Biopsy. In: Current Therapy in Theriogenology: Diagnosis, Treatment and Prevention of Reproductive diseases in Small and Large Animals. Eds: Morrow D A. Saunders, USA.