Historical Control Data of Spontaneous Lesions of Laboratory New Zealand White and Dutch Belted Rabbits () Used in Toxicity Studies.

A retrospective study was performed to determine the incidences of spontaneous findings in control laboratory New Zealand White (NZW) and Dutch Belted (DB) rabbits. Terminal body and organ weights data were also collected. A total of 2170 NZW (526 males/1644 females), 100 DB rabbits (50 animals per sex), aged 4- to 7-month-old were obtained from 158 non-clinical studies evaluated between 2013 and 2022. The NZW rabbits had greater mean terminal body weights than DB strain. Mixed cell infiltration in the lung was the most recorded finding in both strains, followed by pulmonary inflammation/mononuclear cell infiltration. Differentiation between pulmonary "infiltration"/"inflammation" remained challenging as interpretation of guidelines for diagnostic terminology may vary amongst pathologists. Other common findings included mineralization and basophilia of the renal tubules; hepatic/renal mononuclear cell infiltration, all more common in females. Cysts were commonly recorded, with high prevalence in the oviduct, thyroid gland, ovary in NZW strain, while uterine, pituitary gland, and thyroid gland cysts were the most identified in DB rabbits. Neoplasms and infectious etiologies were absent. Most of the animals were sexually mature. To our knowledge, this is the most recent comprehensive study of spontaneous lesions and organ weights in both rabbit strains and should facilitate the differentiation of spontaneous and induced lesions in safety studies.