Transitional vertebrae are congenitally malformed vertebrae situated at junction points between distinct segments of the spine where the vertebrae change shape, as from the ribcage to the lower back or lower back to the hips. This last, the lumbo-sacral region, is the place most transitional vertebrae occur in dogs. Transitional vertebrae will have characteristics typical of both spinal segments. OFA states that “transitional vertebrae are usually not associated with clinical signs.” However, there are reports of Aussies with degenerative disease of the spine in the area of the transitional vertebrae. It may be that these abnormal vertebrae can be subject to increased wear-and-tear in physically active dogs which engage in activities that require spinal flexibility.
Transitional vertebrae are probably inherited. Treat them as a fault. Don’t breed dogs that have them to each other or to dogs with a family history of transitional vertebrae.