The invention provides methods for diagnosing degenerative joint disease in an animal by collecting a saliva sample from an animal; determining the amount of at least one diagnostic agent selected from the group consisting of interferon gamma, interferoninducible protein-10, interleukin-2, and total saliva protein in the saliva sample; comparing the amount of diagnostic agent found in the saliva sample to a corresponding amount of the same diagnostic agent found in a saliva sample from one or more comparable control animals that do not suffer from degenerative joint disease; and diagnosing that the animal is susceptible to or suffering from degenerative joint disease if the amount of diagnostic agent in the saliva sample from the animal is greater than the amount of same diagnostic agent found in the saliva sample from the one or more comparable control animals.