There are LOTS of reasons for abscesses to form, aside from CL. Many cultured will result in common, benign environmental or opportunistic pathogens. You are doing excellent by isolating him from your main herd AND testing the abscesses that occur in your herd.
CL primarily causes abscesses at lymph nodes. The typical site is under the ear on the side of the face, but can form at any lymph node site. Young animals are very susceptible to infection but usually don't show signs as young as 10 weeks of age - or if they do, at main lymph node sites.
My advice is not to panic, and pursue the CULTURE for the abscess contents. Personally here, anything with a bump I know is not from a vaccine, ALWAYS gets cultured AND a CL blood test. (Many CDT vaccines that are NOT CL vaccines will cause a sterile abscess, knot, or baldness at site of injection. Avoid concern by giving all vaccines in the SAME PLACE. For example, all kids get theirs in the right armpit/barrel area, all does and adult stock get theirs in the left armpit/barrel area.)
The blood test is not an end-all-be-all by any means and MUST be interpreted beyond the 'positive' or 'negative' results, and further can be influenced by vaccination for CL. A positive test on an animal with a suspicious lump is good enough for me to diagnose, but that being said, a suspicious lump with a correct herd history is good enough for me to diagnose too.
An additional non-core vaccine (one is available now specific for goats) for CL is an excellent control tool for herds known to be infected, as it REDUCES the number of ACTIVE ABSCESSES and thus reduces the spread of disease indirectly, and clinical illness and the 'wasting' syndrome directly. I do NOT recommend this vaccine to herds that are CL negative as it does NOT prevent new infections directly.
