Spondylosis is a degenerative disease of the spine due to age or injury. Affect dogs develop bone spurs on the vertebrae, sometimes bridging them. Initially dogs are asymptomatic, though you may notice protrusion of the bone spurs. Over time the dog will begin to exhibit pain, stiffness, and restricted motion. Spondylosis can be confirmed with an x-ray. Spondylosis is degenerative and can cause pain. Severe cases can impinge on nerves and may require surgery. For the less affected, it is necessary to restrict activity and manage the pain. Spondylosis can be career-ending for working or performance dogs.
In some breeds it is inherited. However, it is almost always reported in older (7 years plus) Aussies indicating it is an aging and/or wear and tear issue. Unless you are seeing it in multiple related dogs under 7, it is unlikely to be a breeding concern. Should a dog under 7 develop Spondylosis it would be advisable to withdraw that dog from breeding.