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Abdominal Castration in Guinea Pigs 
 

Video at the end

Overview

Castration of male guinea pigs is performed for both elective and medical reasons. The most common indications include:

  • Preventing breeding in mixed-sex households

  • Allowing safe housing with female guinea pigs

  • Reducing hormonally influenced behaviours such as mounting or aggression

  • Treatment of reproductive disease including:

    • orchitis

    • epididymitis

    • testicular neoplasia

    • trauma to the testes

Unlike many domestic species, guinea pigs possess open inguinal canals throughout life. This anatomical feature significantly influences the surgical approach chosen for castration.

Historically, guinea pigs were often castrated via a scrotal approach. However, this technique has been associated with a relatively high rate of postoperative complications, including:

  • Wound dehiscence

  • Surgical site infection

  • Self-trauma

  • Hematoma formation

  • Scrotal swelling

  • Evisceration

  • Inguinal herniation

Because of these risks, many surgeons now prefer an abdominal (caudal midline) approach, which allows the tunic to be securely closed and reduces the risk of postoperative herniation.

Instruments Required

  • 2 × small rat-tooth forceps

  • Metzenbaum scissors

  • Needle holder

  • Scalpel blade

  • Surgical drape

  • 4/0 PDS suture material

Optional but useful:

  • Mosquito haemostats

  • Small gauze swabs

  • Small retractors

Anaesthesia and Premedication

  • The following protocol has been used successfully:

  • Medetomidine: 50 µg/kg

  • Ketamine: 5 mg/kg

  • Morphine: 2 mg/kg

  • Administer via intramuscular injection.

  • This combination provides good sedation, analgesia, and muscle relaxation, facilitating smooth induction.

  • Literature Note

  • Some exotic medicine references suggest slightly lower opioid doses (typically 0.5–1 mg/kg morphine). However, higher doses may still be used safely with appropriate monitoring.

Premedication Protocol

Anaesthetic Maintenance

Once the patient is adequately sedated:

  1. Attach the guinea pig to inhalant anaesthesia.

  2. Maintain using isoflurane in oxygen.

  3. Anaesthetic gas is delivered using a tight-fitting face mask.

At the beginning of anaesthesia, a slightly higher vaporiser setting may be required. Once the patient reaches an appropriate depth, the concentration should be reduced to maintain stable anaesthesia.

Alternative Airway Options

While face masks are commonly used, other options include:

  • Supraglottic airway devices (e.g., V-gel) designed for small mammals

  • Endotracheal intubation, although technically challenging in guinea pigs

Patient Preparation

  1. Position the patient in dorsal recumbency.

  2. Clip the surgical site:

    • Start approximately 1 cm cranial to the umbilicus

    • Extend caudally to the scrotum

  3. Perform a standard aseptic surgical preparation.

  4. Place a sterile drape with a small surgical window.

Because guinea pigs are prone to hypothermia, active warming (heat mat, forced warm air) should be used throughout the procedure

Surgical Technique

Skin Incision

  1. Identify the umbilicus.

  2. The midline incision is started approximately 1 mm caudal to the umbilicus.

  3. Extend the incision 0.3–0.5 cm caudally.

This very small incision is usually sufficient to exteriorise both testes.

Keeping the incision small helps reduce:

  • tissue trauma

  • postoperative pain

  • risk of wound complications.

While making the incision, tense the skin away from the blade to ensure controlled entry.

Once through the skin, a small amount of subcutaneous fat is usually present.

Dissection to the Linea Alba

Using Metzenbaum scissors, bluntly dissect through the subcutaneous tissue until the linea alba is clearly identified.

The linea is grasped gently using rat-tooth forceps and elevated away from the abdominal organs.

Entering the Abdomen

  1. Make a small stab incision into the linea alba.

  2. Once the abdomen is entered, it is common for a small amount of peritoneal fluid to escape. This is normal in guinea pigs.

Care must be taken when entering the abdomen, as the urinary bladder lies immediately beneath the abdominal wall.

Insert the Metzenbaum scissors into the incision and gently spread to enlarge the opening

Locating and Exteriorising the Testicle

This is the step that many surgeons initially find difficult.

Once the abdomen is open:

  1. Gently elevate the abdominal wall.

  2. Look caudolaterally within the abdomen.

  3. A small ivory-white fat pad is usually visible.

This fat pad is attached to the testicle.

Using rat-tooth forceps:

  • Gently grasp the fat pad

  • Slowly exteriorise it through the incision

The testicle will follow the fat pad out of the incision.

Ligation and Removal

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Once the testicle is exteriorised:

  1. Place a single ligature of 4/0 PDS around the spermatic cord.

Important point:

The ligature should be placed proximal to the tunic, ensuring the tunic is included within the ligature.

This helps reduce the risk of postoperative herniation through the inguinal canal.

  1. After the ligature is secured, transect the spermatic cord distal to the ligature using Metzenbaum scissors.

  2. Return the stump gently into the abdominal cavity.

Repeat the same process for the contralateral testicle

 

Closure

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Linea Alba

Close the linea alba using:

4/0 PDS

If the incision has been kept small, one cruciate suture is typically sufficient.

Skin Closure

Close the skin using 4/0 PDS intradermal sutures.

An intradermal closure is preferred because guinea pigs are prone to:

  • chewing external sutures

  • self-trauma to the incision

Ligation and Removal

Administer:

  • Meloxicam: 0.5 mg/kg SC

  • Metoclopramide: 1 mg/kg

The patient is discharged with:

  • Meloxicam (Loxicom): 0.5 mg/kg PO once daily for 5 days

Postoperative Care

Owners should monitor for:

  • appetite

  • faecal production

  • activity level

  • swelling at the surgical site

Guinea pigs are particularly prone to postoperative gastrointestinal stasis, so ensuring early return to feeding is critical.

Recommended care includes:

  • unlimited hay

  • fresh vegetables

  • minimal stress

  • warm environment

If appetite decreases, assisted feeding may be required.

Common Intraoperative Challenges

Difficulty Finding the Testicle

The most common reason surgeons struggle is not identifying the fat pad.

Tips:

  • Look caudolaterally, not directly beneath the incision.

  • The fat pad is often small and ivory coloured.

  • Gentle traction usually brings the testicle into view.

Fat Pad Tears

If the fat pad tears:

  • Carefully explore the area with blunt forceps

  • The spermatic cord can still usually be located nearby

Bladder Interference

Because the bladder lies directly beneath the incision:

  • Ensure the bladder is emptied before surgery

  • Enter the abdomen cautiously

Possible Complications

Even with the abdominal approach, potential complications include:

Surgical complications

  • Hemorrhage

  • Damage to abdominal organs

  • Incomplete ligation of spermatic cord

Postoperative complications

  • Wound infection

  • Dehiscence

  • Self-trauma

  • Gastrointestinal stasis

  • Rarely, inguinal herniation

The abdominal approach significantly reduces the risk of herniation and evisceration compared with scrotal techniques.

Anaesthetic Monitoring Recommendations

Because guinea pigs are sensitive to anaesthesia, monitoring should ideally include:

  • heart rate

  • respiratory rate

  • oxygen saturation (pulse oximetry)

  • body temperature

Hypothermia is a very common intraoperative issue, so active warming is strongly recommended.

Disclaimer

This material is intended for veterinary professionals and students. Surgical procedures should only be performed by trained clinicians with appropriate anaesthetic monitoring and facilities.

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