Auricular chondropathy in rats at a contract research toxicology laboratory.

The veterinary staff at WIL Research Laboratories, LLC, was asked to assess and characterize a condition of swollen and reddened ears that had been observed in some of the rats in our facility. When all of the Crl:CD(SD) rats in the facility were examined in August of 2004, August of 2005, and February of 2007, the incidences were 0.25%, 0.18%, and 0.19%, respectively. The overall incidence was 0.21%, with a total of 51 of 24677 animals affected. Only bilaterally affected animals were considered positive. Incidence was strongly correlated with the presence of an ear tag. All but one of the affected animals had an ear tag present. Severe auricular chondropathy was diagnosed on microscopic exam.