Factors contributory to death of young Sprague-Dawley rats in carcinogenicity studies

It is often difficult to determine the cause of early or sporadic deaths in toxicity studies or animal experiments. To help in the interpretation of early deaths, it is critical that the background incidence of factors contributory to death be recorded and archived. Information was collected from the control groups of 20 carcinogenicity studies using Sprague-Dawley (SD) rats. From a total of 1284 males and 1264 females, 46 male (3.58%) and 44 female (3.48%) decedents were recorded during the first 50 weeks of study. There was no difference between the sexes in the probability of survival. The factors contributory to death were neoplastic in 17 males (37%) and 35 females (79.5%), non-neoplastic in 12 males (26.1%) and 3 females (6.8%) and unknown in 17 males (37%) and 6 females (13.6%). Of the neoplastic lesions, pituitary adenoma and mammary tumours in females were most common, followed by malignant lymphoma and brain tumours in both sexes. Some interesting and comparatively rare tumours were also seen. Death due to non-neoplastic lesions was most often associated with lesions of the urogenital tract, liver and skin. A small number of animals died due to trauma or anaesthetic accident, or were killed because of poditis. A comparatively large proportion of decedents were found dead without any determinable cause of death. This report is intended to be of use to toxicologic pathologists in assessing factors contributory to death in young rats in short-term studies, and more especially to provide a reference to the background profiles of tumour in such animals.