Swollen Testicles

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What Are Swollen Testicles?

A male rabbit’s, or buck’s, testicles are naturally relatively large (averaging 15x35mm). However, they can increase in size or shape for a number of reasons, some of which are completely normal and some of which could be signs of disease.

When is it normal?

There are some instances where a normal buck’s testicles may change in size or shape. These include:


During gestation, a male’s testicles develop inside the abdominal cavity and do not descend into the scrotum until after birth. In bucks, this takes place 2-3 months after birth. If you have a young rabbit who suddenly develops large testicles, this may be because they have fully descended. Like other male mammals, the testicles also increase in size at puberty, reaching their maximum dimensions at sexual maturity (perhaps 6-8 months in bucks).

Normal movement:

Unlike many other mammals, the canal connecting the abdomen to the scrotum (the inguinal canal) does not fully close after the testicles descend. This means a buck’s testicles can travel back up the inguinal canal slightly. Bucks often retract their testicles back into the inguinal canal to keep the testicles warmer on cold days and let them descend when it is warm.

The testicles also get retracted when he is fighting or scared, outside of the rabbit breeding season (Spring-Summer), or has a full stomach. This movement, especially due to temperature changes or stress, can easily be confused with changes in the size of the testicles.

Post-neutering swelling:

After your buck has been castrated (surgical removal of the testicles to prevent breeding and breeding behaviour), the leftover scrotum can sometimes swell slightly, due to inflammation. A small amount of swelling is normal and will go away in a few days. However, if there is significant heat or swelling, any pain or discomfort, or any discharge, please let your vet know straight away.

Other Causes

As well as the normal causes of swollen testicles, there can be causes related to disease. Problems may include:


A buck’s testicles can become infected by bacteria, which causes swelling, pain, heat and discharge – this is also called infectious orchitis or epididymitis, depending which specific part of the testicles are infected. Bacteria can enter the testicles via damage to the surrounding area, such as from a bite; they can also spread from another location via the bloodstream. Generally, the latter will cause more systemic signs of disease such as an increased temperature, dehydration and lethargy. Significant infections can lead to formation of an abscess, which is a large sealed area of bacteria-filled pus – abscesses can cause a lot of swelling. Testicular infections are usually treated with antibiotics.


A specific form of testicular infection caused by the bacterium Pasteurella multocida. This bacterium often spreads from mothers to young rabbits, via infected food, water, the environment or the air. It mainly causes respiratory tract disease such as difficulty breathing, eye and nasal discharge, increased breathing rate and a head tilt. However, the bacteria can spread in the blood to other parts of the body and cause abscesses, including the testicles. Pasteurellosis can be treated with antibiotics and anti-inflammatory drugs. Some rabbits respond well on treatment but others less so.


The testicles and surrounding tissue can become inflamed without bacterial infection, termed non-infectious orchitis or epididymitis. Common causes include bites or scratches from other rabbits, self-trauma, damage from the environment, or overheating of the area. There will be swelling, heat and pain, but generally no discharge. Inflammation can be treated with rest, cold compresses, bandaging and anti-inflammatory drugs.

Rabbit syphilis:

This is a disease caused by a bacterium called Treponema cuniculi – it is spread from rabbit to rabbit during sexual reproduction, but can be spread via non-reproductive close contact. It causes crusty lesions on parts of the nose, lips, eyelids, anus and genitals, including the testicles. These scabs can make it look like the testicles have swollen up. Treatment is via an antibiotic called penicillin. For breeders of rabbits, always check both rabbits are free of this disease before allowing them to come into close contact.

Hutch burn/urine scald:

This is a disease where the skin on a rabbit’s rear end starts to become raw and infected, due to burning from chemicals in urine. The infection of the skin can appear like swollen testicles. It usually indicates that your rabbit’s hutch is not clean – consider cleaning it thoroughly and more often, and placing down more bedding material to soak up excess urine. Hutch burn can rarely be caused by an inability for your rabbit to urinate properly, such as obesity, arthritis or urinary tract issues.

Inguinal hernia:

Because a buck’s inguinal canal does not close fully, it is possible for abdominal organs, such as intestines, to travel into the inguinal canal or even the scrotum, and get trapped. Usually the testicles prevent this, but it does occur in castrated bucks if the inguinal canal was not surgically closed, and occasionally in entire bucks as well. This swelling will be soft, generally and can be pushed back. It is an emergency, as the trapped organs can start to degrade, so immediate veterinary care is needed.


Finally, bucks can sadly get testicular cancers like other mammals. Testicular cancer generally causes a slowly increasing swelling that is not painful or inflamed, as well as irregularly-shaped testicles. It can occur in both or one testicles – if it occurs in just one, the healthy testicle can sometimes shrink in size. The cancer can cause an overproduction of sexual hormones, which can cause changes in behaviour. Testicular cancer can spread to the lungs if it progresses, which usually means the rabbit must be euthanased. Treatment of testicular cancer usually involves castration. Thankfully, testicular cancer occurs mainly in older rabbits, and is relatively rare.

A Note on Neutering:

Bear in mind that a buck that is castrated cannot get many diseases of the testicles. It does not prevent infection or inflammation of the tissue that remains or systemic diseases like Pasteurellosis, but will prevent cancers, orchitis and similar diseases. Many vets recommend all rabbits are castrated to prevent accidental breeding or fighting as well. See the Neutering factsheet.