Each disc has a tough outer layer and a gel-like centre. In chondrodystrophic breeds (dogs with short legs and long backs), discs can harden and calcify early in life, making them prone to sudden rupture. The American College of Veterinary Surgeons notes that Dachshunds account for 45–70% of cases, usually at 3 to 6 years old. Other at-risk breeds include the Pekingese, Beagle, Lhasa Apso, French Bulldog, Shih Tzu and Corgi.
In larger breeds such as Labradors and German Shepherds, discs tend to degenerate more slowly and bulge gradually, typically in dogs aged 5 to 12.
ACVS describes a predictable progression of signs: back or neck pain, then a wobbly "drunken sailor" walk, then loss of the ability to walk (usually with loss of bladder control), and finally loss of pain sensation, a sign of severe spinal cord injury.
