Healthy dog testicles are naturally firm, uniform organs that aren’t particularly soft or squishy. Ultrasound studies of normal canine testes describe them as firm and not very pliable. So if your dog’s testicles simply feel solid but are symmetrical, pain-free, and the same size they’ve always been, that may be completely normal. But if you’re noticing a change, if one or both testicles have become noticeably harder, larger, lumpy, or painful, several conditions could be responsible.
What Normal Dog Testicles Feel Like
A healthy testicle is smooth, oval-shaped, and moderately firm, similar to the firmness of a hard-boiled egg. Both testicles should be roughly the same size, sit freely in the scrotum, and move slightly when you gently press on them. The key things to watch for are changes: a testicle that used to feel one way and now feels different, one that’s suddenly bigger than the other, or any sign of pain when you touch the area.
Infection and Inflammation
One of the most common reasons a dog’s testicle becomes noticeably hard and swollen is orchitis (infection of the testicle) or epididymitis (infection of the tube that stores sperm next to the testicle). These are usually caused by bacteria, though fungal and viral infections can also be responsible. The bacteria can reach the testicle through the bloodstream, travel up from the urinary tract, or enter through a wound like a bite or scrape.
In acute cases, your dog will likely show obvious signs of distress. In a study of 14 dogs with epididymitis, scrotal swelling appeared in 12 cases, scrotal pain in 10, and lethargy or loss of appetite in 11. Fever, redness, and purulent discharge from the penis are also possible. Some dogs walk stiffly or become lame because of the pain. In severe cases, the infection can become life-threatening if it spreads to the bloodstream.
Chronic infections are trickier to spot. They can cause the testicle to feel enlarged and hard without any obvious pain or redness. Over time, chronic inflammation leads to scarring and fibrosis, which makes the tissue permanently stiff. If your dog’s testicle has been gradually getting firmer over weeks or months without other symptoms, a low-grade chronic infection is one possibility.
Treatment typically involves antibiotics for three to four weeks, chosen based on what bacteria are causing the problem. If your dog isn’t being used for breeding, neutering is often the most straightforward solution. For breeding dogs with only one affected testicle, removing just that testicle can preserve some fertility. Even with successful treatment, damage to the reproductive tissue can take months to fully reveal itself.
Testicular Tumors
Testicular tumors are the most common reproductive tumors in male dogs. The three main types are Leydig cell tumors, seminomas, and Sertoli cell tumors. These tend to show up in older, intact (unneutered) dogs, though they can occur at any age.
A tumor typically makes one testicle feel harder, larger, or lumpy compared to the other. The growth is usually painless, which is why many owners don’t notice it until the testicle is significantly enlarged. Sertoli cell tumors and seminomas are the types most often caught during a physical exam because they produce more obvious changes in size and firmness. Leydig cell tumors are very common but tend to be small and are frequently found only at necropsy.
Sertoli cell tumors deserve special attention because they can produce estrogen, leading to additional signs like hair loss (often symmetrical on both sides of the body), a swollen prepuce, attraction of other male dogs, or even bone marrow suppression in advanced cases. If your dog has a hard testicle along with unusual hair thinning, that combination is a red flag.
Dogs with undescended testicles (cryptorchid dogs) are at significantly higher risk for tumors. An undescended testicle sits in the abdomen or inguinal canal where temperatures are higher, which promotes abnormal cell growth. If your dog has one testicle that never dropped and you feel a firm mass in the groin or notice abdominal swelling, a tumor in the retained testicle is a strong possibility.
The good news is that most testicular tumors in dogs are benign and curable with neutering. Malignant spread is uncommon, though it does happen, which is why early evaluation matters.
Testicular Torsion
Torsion happens when the spermatic cord twists, cutting off blood flow to the testicle. This is an emergency. The testicle swells rapidly, becomes very hard, and is extremely painful. Your dog may show abdominal pain, vomiting, loss of appetite, lameness, or a stiff gait. In some cases with only a partial twist, the signs can be milder or even absent initially.
Dogs with undescended testicles are more prone to torsion because the testicle isn’t anchored in the scrotum. If the affected testicle is still viable, a vet can sometimes untwist it and secure it in place surgically. But if the tissue has lost blood flow for too long, removal is necessary. For any undescended testicle that twists, removal is always recommended.
Scrotal Hernia
Less commonly, what feels like a hard testicle is actually a scrotal hernia, where abdominal contents like fat or a loop of intestine push down into the scrotum. This makes one side of the scrotum feel swollen and firm. On examination, a hernia can look very similar to a testicular mass or infection. Palpation usually causes a pain response, though if nothing is trapped or pinched, your dog may tolerate handling with only mild discomfort. Scrotal hernias typically need surgical repair.
How Vets Figure Out the Cause
Your vet will start with a physical exam, feeling both testicles for symmetry, texture, and pain response. Ultrasound is the most useful next step. It can reveal internal changes like irregular tissue patterns, fluid buildup around the testicle, small calcified spots, cysts, or abscesses. These findings help distinguish between infection, tumor, torsion, and hernia.
Blood work can show signs of systemic infection or, in the case of Sertoli cell tumors, elevated estrogen levels. If a mass is found, a fine needle aspirate (inserting a small needle to collect cells) can sometimes identify the type of growth before surgery. In many cases, though, the definitive diagnosis comes after the testicle is removed and examined under a microscope.
What You Should Watch For
A few signs that mean your dog needs to see a vet soon rather than later:
- Asymmetry: one testicle is clearly larger or firmer than the other
- Pain: your dog flinches, yelps, or pulls away when the area is touched
- Swelling or redness: the scrotal skin looks puffy, hot, or discolored
- Behavioral changes: lethargy, refusing food, stiff walking, excessive licking of the area
- Discharge: any fluid coming from the penis that isn’t urine
Sudden onset of severe pain with vomiting or a hard, swollen testicle that appeared within hours suggests torsion and warrants an emergency visit. Gradual, painless enlargement is more typical of a tumor or chronic infection, but still needs evaluation. The earlier any of these conditions is caught, the better the outcome and the more options you’ll have for treatment.