Trends in mortality, body weights and tumor incidences of Wistar rats over 20 years.
Historical data of more than 8,000 Wistar rats (designation: WISW SPF Cpb) used as controls in seventy 2-year studies terminated between 1975 and 1994 were analyzed for time trends in food consumption, terminal body weight, mortality, and tumor incidences. In males there was a significant (p < 0.01) time trend towards higher terminal body weight and a tendency (p > 0.05) to lower incidences of pituitary tumors and adrenal pheochromocytomas, while mortality remained stable. Leydig cell tumors showed a significant (p = 0.0005) positive trend. In females, terminal body weight did not increase over time but pituitary and mammary tumors showed a marked and highly significant (p = 0.0001) increase, which explains a significant (p = 0.0045) positive trend in mortality. There was a significant (p = 0.0001) negative time trend for uterine adenomas/carcinomas and a slight tendency (p = 0.4135) towards a decreased incidence of endo-metrial stromal polyps. Since the average food intake data do not indicate a time trend the changes observed might probably not be related to higher caloric intake. In contrast to other authors we could not find a positive correlation between either body weight and incidences of pituitary tumors or body weight and mortality. Certain selection measures at breeding and/or a genetic drift over time might explain the time trends observed. This data does not yet indicate a need for a change in ad-libitum feeding of these animals.
Eiben
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Bayer AG, Institute of Toxicology, Wuppertal, Germany.
Bomhard
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D000818:Animals; D001835:Body Weight; D004032:Diet; D005260:Female; D008297:Male; D009026:Mortality / Q000639:trends; D009369:Neoplasms / Q000453:epidemiology / Q000401:mortality / Q000662:veterinary*; D010911:Pituitary Neoplasms / Q000453:epidemiology / Q000401:mortality / Q000662:veterinary; D051381:Rats; D017208:Rats, Wistar / Q000235:genetics / Q000502:physiology*; D012641:Selection, Genetic