Thymectomy should be the first choice in the protection of diabetes-prone BB rats for breeding purposes.

Diabetes-prone (DP)-BB rats spontaneously develop diabetes and are widely used as an animal model for the study of type I diabetes. Since DP-BB rats develop diabetes before or at the time of breeding, such rats used for breeding need to be protected against diabetes development by the transfer of regulatory T cells obtained from diabetes-resistant (DR)-BB rats, by insulin treatment or by thymectomy. Thymectomy of juveniles is not commonly used to protect DP-BB rats, and we investigated whether breeding with thymectomized DP-BB rats was a realistic alternative to the two other methods. No differences in pregnancy rates, numbers of pups per litter or growth rates of pups were found. Moreover, no differences were found in diabetes development in the offspring. Protection of juvenile DP-BB rats by thymectomy is comparable to the other established procedures, is simple and safe, and the rats recover well from the procedure. Breeding with thymectomized animals will reduce the number of animals needed, and it improves the well-being of the animals because it reduces the negative side effects associated with the other procedures such as episodes of hypo and hyperglycaemia. Therefore, although thymectomy is an invasive procedure, we would like to recommend weanling thymectomy as the first choice for the protection of DP-BB rats for breeding purposes.