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Ultrasonography: reproductive tract – male

ISSN 2398-2977

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Synonym(s): Ultrasonography of the male reproductive tract


  • Not used routinely at the present time in stallions, but rapidly increasing in popularity.


  • A useful adjunct to stallion breeding-soundness examination   Male: genitalia - examination  .
  • An important diagnostic tool for examination of reproductive pathology in the stallion.


  • technique allows for inspection of internal reproductive organs.
  • Non-invasive examination of components of the male reproductive system.


  • Rectal palpation involves risk to examiner and animal.
  • Examination of the external genitalia often requires the veterinary surgeon to be in a potentially vulnerable position in relation to the horses hind legs and therefore proper restraint   Restraint methods  is essential and extreme care must be taken of personnel and equipment.
  • Experience is needed to perform the technique and interpret the ultrasound images.
  • Narrow scope of result findings, ie structural abnormalities.

Technical problems

  • Transducer size and frequency will limit results achievable.
  • Interpretation of ultrasound scans requires a high level of expertise.

Alternative techniques

  • Manual palpation.
  • Rectal palpation.
  • Testicular biopsy.

Decision taking

Risk assessment

  • Examination of the external genitalia often requires the veterinary surgeon to be in a potentially vulnerable position in relation to the horses hind legs and therefore proper restraint   Restraint methods   is essential and extreme care must be taken of personnel and equipment.
  • Rectal palpation involves risk for both personnel and horse.



Veterinarian expertise

  • High.

Other involvement

  • An experienced stallion handler should restrain the stallion throughout.
  • The ultrasound machine should be placed on a movable trolley with a person on-hand for its rapid removal should the stallion misbehave; this person could usefully be employed as scribe to allow the veterinary surgeon uninterrupted/swift examination time.

Materials required

Minimum equipment

  • Linear-array with 5.0 or 7.5 MHz transducer.
  • Sector scanners can be used but the curved surface of the transducer can make positioning difficult.
  • Coupling gel specifically designed for ultrasound.

Ideal equipment

  • A 7.5 MHz transducer is ideal.
  • A 10 MHz transducer may give better visualization of superficial structures, eg epididymis, in some cases.
  • A wide-bandwidth 6 MHz microconvex linear-array transducer will provide excellent resolution with a wide field of view for comparing right and left sides.

Ideal consumables

  • Although a lubricant formulated for perirectal palpation is useable, it may form a bubble filled with foam when in contact with a sweaty surface - ultrasound gel is preferred.


Site preparation

  • Bandage tail   Tail: bandage  to prevent soiling from rectal examination or hairs interfering with approach.

Other preparation

  • Carry out a routine rectal examination   Urogenital: rectal palpation   of the internal genitalia under proper restraint.
  • If semen sampling   Semen: collection   is also required perform this prior to ultrasound examination the stallion will be more relaxed and the external genitalia will be easier to handle.


  • Back the horse into a corner with the right side against a wall this prevents the horse from twisting or backing and discourages kicking.
  • The handler should stand on the near side of the horse on a level with the shoulder, beyond the range of striking distance of the forefeet, and control twisting of the horse by applying pressure to the shoulder.
  • Twitch   Restraint methods  /chemical restraint if required   Anesthesia: standing chemical restraint  .
  • Alternatively stocks with removable side rails/panels can be used.



Step 1 - Palpate external genitalia

  • Examine testicles, epididymis, spermatic cord and inguinal region visually and by palpation   Male: genitalia - examination  .
  • Identify any obvious abnormalities which require specific ultrasound examination.

Core procedure


Step 1 - Examine left testicle

  • Apply coupling gel to transducer.
  • Approach stallion from left shoulder, maintaining contact with stallion along length of side; slowly crouch in front of the stallions hind legs and use left hand to hold left testicle firmly whilst pushing right testicle out of the way.
  • Place transducer firmly against lateral surface of testicle perpendicular to its long axis.
  • Move transducer slowly several times over the entire lateral surface of the testicle the entire long axis is too large in most cases to visualize in a single frame.
  • If the testis is not relaxed, the tail of the epididymis can be difficult to visualize place the transducer either directly over the tail (not always easy because of location on curved caudal pole of testicle) or over testicle just cranial to tail using the testes as a standoff, direct beam caudally towards tail.
  • During the examination of the testicles measure right and left testicular width, height and length and the total scrotal width.

Step 2 - Examine spermatic cord

  • Gently but firmly apply downward traction to the left testicle using the left hand.
  • Holding the transducer in the right hand, move further up into the inguinal region and position over the spermatic cord, parallel to the ground, providing short-axis cross sections of the cord.
  • Slowly move transducer up and down cord as far as safely possible.
  • Position transducer parallel to cord (7.5 MHz transducer) for long-axis sections.

Step 3 - Examine right testicle and spermatic cord

  • Repeat steps 2 and 3 above to examine the right testicle and spermatic cord repositioning of the horse and equipment may be necessary to approach the stallion from the right hand side.
  • The normal ultrasonographic appearance of the testicle:
    • Testicular parenchyma is homogenous, gray and granular.
    • A small amount of anechoic fluid is normally present in the vaginal cavity between the visceral and parietal tunicae.
    • The central vein is usually visible as an anechoic line traversing the approximate center of the parenchyma. It is most easily seen at the cranial aspect of the testis.
    • The parietal vaginal tunic and its associated structures appear as a hyperechoic line outside the vaginal cavity.
  • The normal ultrasonographic appearance of the epididymis:
    • Very heterogeneous and gray-black in color and has a mottled "swiss cheese" appearance.
    • The lumen is largest in the tail.
  • The normal spermatic cord: 
    • Has a very heterogeneous appearance with distinct anechoic areas surrounded by more hyperechoic areas.
    • Blood flow may be detected in the lumina of the vessels.

Step 4 - Examine accessory glands per rectum

  • After emptying the rectum and examining the accessory glands manually using a well-lubricated, gloved hand/arm, gently introduce the lubricated transducer into the rectum. A 7.5 MHz linear array transducer provides excellent detail.

Rectal tears are a rare but inherent risk during any peri-rectal examination.

Unless a probe designed for rectal examination is used, protecting the transducer with a plastic sleeve will facilitate cleaning after the examination.

  • Place the transducer over the accessory glands to identify and visualize the ampullae, pelvic urethra, seminal vesicles, prostate gland and ductus deferens.
  • The normal ampullae:
    • Longitudinal section - transducer placed directly on top of gland, angled slightly off midline to parallel gland:
      • A narrow, gray-white, homogenous band extending from left to right across screen.
      • Occasionally lumen is visible as a thin black (containing fluid) or white (no fluid) line through the center of gland.
    • In cross-section: transducer turned at 90º to long axis of gland the smaller 7.5MHz transducer is best for this.
  • The normal pelvic urethra - caudal region of ampullae in the midline:
    • A roughly circular, gray-white structure medial and ventral to cross-sections of the ampullae.
    • The urethral lumen may be visible in cross-section as an echoic (empty) or anechoic (full of urine) spot in center of urethra.
  • The normal seminal vesicles - slightly caudal and lateral to ampullae:
    • The walls appear gray-white and homogeneous.
    • Entire gland flattened dorsally and ventrally.
    • Varying amounts anechoic fluid content in lumen.
  • The normal prostate gland - isthmus is in midline caudal to neck of seminal vesicles; lobes lateral:
    • Parenchyma appears gray-white and heterogeneous, containing multiple anechoic spaces (fluid).
  • The normal bulbourethral glands - to the right and left of the mid-line caudal to prostate, just within the anal sphincter:
    • Circular, granular, gray-white.
  • Examine inguinal rings at same time. Identify each ductus deferens as it runs out of the internal ring like a tense string. Each ductus can be traced caudally from the rings to the ampullae.



Step 1 - Remove transducer

  • Gently remove transducer from the rectum.
  • Clean perineal area of feces and lubricant.


Immediate Aftercare


  • None required.


Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Resende H L et al (2014) Determination of equine fetal sex by Doppler ultrasonography of the gonads. Equine Vet J 46 (6), 756-758 PubMed
  • Schambourg M A, Falrey J A, Marcoux M & Laverty S (2006) Use of transabdominal ultrasonography to determine the location of cryptorchid testes in the horse. Equine Vet J 38 (3), 242-245 PubMed.

Other sources of information

  • Reef V B (2003) Ed. Equine Diagnostic Ultrasound. W B Saunders. ISBN: 0721650236.
  • Rantanen N W & McKinnon A O (1998) Eds. Equine Diagnostic Ultrasonography. Lippincott, Williams & Wilkins. ISBN: 0683071238.