Abstract
To help the interpretation of causes of death, it is critical that the background incidence of factors contributing to death be recorded and archived. Information was gathered from the control groups of 19 rat carcinogenicity studies. All cases of death occurring within the 2-year period were reviewed. Out of 1124 males and 1084 females, 720 male (64.1%) and 689 female (63.6%) decedents were recorded. There was no difference in the probability of survival between two sexes. Analysis of factors contributing to death revealed that 400 males (48.7%) had neoplastic changes, 189 males (23.0%) had non-neoplastic lesions, and 232 males (28.3%) died from unknown causes. In females, these figures were 627 (76.4%), 62 (7.6%) and 132 (16.0%), for neoplastic, non-neoplastic and unknown findings, respectively. It could be suggested that the risk of death by non-neoplastic reasons was higher in the males than in the females, whereas females were more likely to be affected by tumours. In the neoplastic causes of death, pituitary tumours were the most common in both sexes, followed by mammary tumours in females, and haemopoietic tumours in males. In non-neoplastic cause of death, renal diseases were the most common in both sexes, followed by skin diseases and cardiovascular diseases in males, and skin diseases and poditis in males. A relatively large number of animals (28.3% in males and 16.0% in females) were found dead, without any significant clinical or histologically identifiable cause. Most of the animals with pituitary tumours were killed in extremis and the proportion of females (70.1%) being greater than males (46.8%). There were no case which died by accident, and also only minimal incidence which died by bleeding procedures.