Testing goats for caseous lymphadenitis (CL) involves three main approaches: physical examination, bacterial culture of abscesses, and blood tests that detect antibodies. The method you choose depends on whether your goat has a visible abscess or you’re screening an apparently healthy animal before adding it to your herd.
Physical Examination: The First Step
A hard lump near a lymph node is the most recognizable sign of CL in goats. The most common locations are behind the ears, under the jaw or along the neck, on the shoulders, and in the rear flank area. Run your hands over these areas regularly, especially before purchasing a new animal or when you notice a goat losing condition.
A firm, non-painful swelling in one of these spots is highly suggestive of CL, but it’s not proof. Other bacteria can cause abscesses in the same locations, and not every lump is an abscess. Physical exam alone can’t give you a definitive answer, which is why further testing matters.
Abscess Culture: The Most Reliable Test
Bacterial culture of pus from an intact abscess is the gold standard for CL diagnosis. It’s the only way to confirm that the specific bacterium responsible for CL is actually present. If your goat has a visible abscess, this is the test to pursue.
The sampling procedure is straightforward but requires care to avoid spreading the bacteria. Clip the fur over the abscess and disinfect the area with alcohol. Wearing gloves, insert an 18-gauge needle attached to a syringe into the center of the abscess and draw back to collect pus. You may need to move the needle around slightly. One important clue comes during this step: CL pus is characteristically thick, almost paste-like. If the material you draw back is thin and liquid, it’s likely not CL. Don’t expect to drain the abscess through the needle. You may only collect a small amount in the syringe, and that’s enough.
Recap the needle carefully and submit it to a veterinary diagnostic lab for culture or staining. The lab will grow the bacteria and identify whether it’s the CL organism. This typically takes a few days to a week depending on the lab. The key advantage of culture is its accuracy: if the lab grows the bacterium, you have your answer. The limitation is that you need an active, intact abscess to sample.
Blood Tests for Goats Without Abscesses
When a goat has no visible abscess, or when you want to screen a group before buying, blood testing (serology) is the way to go. These tests detect antibodies the goat’s immune system produces in response to the CL bacterium, rather than finding the bacterium itself.
The two main blood tests are the Synergistic Hemolysin Inhibition (SHI) test and the ELISA. The SHI test, offered by labs like Washington State University’s diagnostic lab, measures antibodies against a toxin produced by the CL bacterium. ELISA tests work on a similar principle but use different target proteins. Recent ELISA methods have achieved about 96% sensitivity and 94% specificity in goats, meaning they correctly identify most infected animals while producing relatively few false positives.
To run either test, your vet draws a standard blood sample and ships the serum to a diagnostic lab that offers CL serology. Not all labs run these tests, so check availability before collecting samples.
Timing Matters for Blood Tests
Blood tests won’t catch a newly infected goat right away. After exposure, it takes at least 15 to 25 days before antibodies reach detectable levels. If you’re testing a goat that was recently exposed, a negative result in the first two weeks doesn’t rule out infection. Retesting three to four weeks after potential exposure gives a more reliable picture.
Age also plays a role. Kids under six months old can test falsely positive because they carry maternal antibodies passed through colostrum. Those antibodies fade over time but can trigger a positive result on serology even in an uninfected kid. Wait until after six months of age for meaningful blood test results.
How Vaccination Affects Test Results
If a goat has been vaccinated against CL, it will produce antibodies that look the same on a blood test as antibodies from a real infection. Vaccinated goats will test positive on standard serology. This makes it difficult to distinguish a vaccinated, healthy goat from a truly infected one using blood tests alone. If you’re buying goats and the seller mentions CL vaccination, factor that into how you interpret any serological results. Knowing the vaccination history of your herd and any incoming animals is essential for making sense of blood work.
Detecting Internal CL
CL doesn’t always show up as external lumps. The bacterium can form abscesses on internal organs and lymph nodes, particularly in the lungs, liver, and kidneys. Internal CL is harder to detect because there’s nothing to see or feel from the outside. Affected goats may slowly lose weight, develop a chronic cough, or simply fail to thrive without an obvious cause.
Blood tests are the primary screening tool for internal CL since there’s no abscess to sample. A positive blood test in a goat with unexplained weight loss or poor condition raises strong suspicion. Ultrasound can sometimes reveal internal abscesses, though this requires veterinary equipment and expertise that may not be available in all rural settings. In many cases, internal CL is only confirmed at necropsy.
Choosing the Right Test for Your Situation
Your testing strategy depends on what you’re dealing with. If a goat in your herd has a suspicious lump, go straight to abscess culture. It gives you the most definitive answer and tells you exactly what organism you’re dealing with. Keep the abscess intact until you can sample it, because a ruptured abscess contaminates the environment and makes clean sampling harder.
If you’re screening new animals before bringing them onto your property, blood testing is the practical choice. Draw blood at least two to three weeks after any known exposure window, and ideally test animals that are over six months old. Some producers test incoming goats twice, several weeks apart, to catch animals that may have been in the early window of infection during the first draw.
For herd-wide screening, combining both methods gives the fullest picture. Culture any active abscesses you find, and blood-test the rest of the herd. No single test is perfect, but using them together significantly reduces the chance of missing an infected animal.