Immune-Mediated Orchitis in Pigs: Testicular Inflammation and Fertility Risks

Immune-mediated orchitis is inflammation of the testicle that happens when the immune system targets testicular tissue instead of protecting it. In pigs, this is considered uncommon and is usually a diagnosis your vet reaches only after more common causes of orchitis, such as trauma or infection, have been investigated. In breeding boars, testicular inflammation matters because swelling can be followed by firmness, loss of normal resiliency, and eventual atrophy, all of which can reduce semen quality and fertility.

The condition may affect one testicle or both. Early on, a pig may show pain, warmth, and enlargement of the scrotum. Later, the testicle can become smaller and firmer as damage progresses. That change is important because asymmetry and atrophy are linked with poorer sperm production and abnormal semen findings in boars.

For pet pigs, the main concerns are pain and comfort. For breeding pigs, there is the added concern of reduced conception rates, poor semen quality, or infertility. Because several infectious causes of orchitis in swine can also affect herd health and, in some cases, people, your vet will usually approach this as a rule-out process rather than assuming it is immune-mediated from the start.

In immune-mediated orchitis, the immune system reacts against testicular tissue. This may happen after the normal barrier that protects sperm cells from the immune system is disrupted. In practical terms, that means inflammation can sometimes follow earlier injury, infection, heat stress, or other damage that exposes testicular antigens and triggers an abnormal immune response.

In pigs, your vet will usually first look for more common triggers of orchitis. Merck notes that boar testicles can be affected by trauma and by infectious diseases such as brucellosis and actinobacillosis. Swine brucellosis is especially important because it can cause orchitis, infertility, and swelling of accessory sex glands, and it also carries zoonotic risk. Fever from any illness can also disrupt testicular thermoregulation and contribute to temporary subfertility.

Because of that, immune-mediated orchitis is best thought of as a diagnosis of exclusion. If cultures, herd history, physical findings, and other testing do not support infection, and the pattern fits sterile inflammation with ongoing testicular damage, your vet may consider an immune-mediated process. The exact trigger is not always found.

Diagnosis starts with a full history and physical exam. Your vet will ask about breeding performance, recent illness, fever, injury, transport, fighting, housing, and any herd-level reproductive problems. In boars, a breeding soundness evaluation is often part of the workup because changes in semen quality can help show how much the testicles have been affected.

On exam, your vet will palpate the scrotum and testicles for size, symmetry, firmness, heat, and pain. Merck notes that swelling is an early response to trauma or infection, while chronic damage can lead to increased firmness, loss of resiliency, and atrophy. Semen evaluation may show low sperm numbers, poor motility, or abnormal sperm forms when fertility has been affected.

Additional testing may include bloodwork, ultrasound, and targeted infectious disease testing based on risk. Ultrasound can help assess enlargement, tissue changes, fluid, or focal lesions and can also guide sampling if needed. If infection is suspected, your vet may recommend culture or other laboratory testing. In selected breeding animals, biopsy or aspirate may be considered, but only after less invasive testing and only when the result would change management. A diagnosis of immune-mediated orchitis is usually made after infectious, traumatic, and neoplastic causes have been ruled out as much as possible.

Not every case can be prevented, because immune-mediated inflammation may develop after hidden or unavoidable tissue injury. Still, prevention focuses on reducing the events that can trigger testicular damage in the first place. Good housing design, calm handling, and limiting fighting between intact males can help reduce trauma to the scrotum and testicles.

Breeding boars benefit from routine reproductive checks. Merck recommends breeding soundness evaluation and careful examination of the testicles for size, symmetry, consistency, and pathologic change. Catching swelling, asymmetry, or declining semen quality early may allow your vet to intervene before long-term atrophy develops.

Biosecurity also matters. Work with your vet on herd health, quarantine practices, and testing when infectious reproductive disease is a concern. Because swine brucellosis can cause orchitis and infertility, any intact male pig with testicular swelling should be evaluated promptly rather than watched at home. Keeping pigs comfortable during hot weather and addressing any illness that causes fever may also help protect testicular function.