Abstract
Two-year studies were undertaken in Sprague-Dawley (SD) rats to assess the effects of origin, group housing, or various feeding regimens on longevity. This report describes results of in-life findings pertaining to body weight gain, food consumption, palpable masses, and preliminary analysis of clinical pathology parameters and necropsy observations. The first study compared ad libitum feeding of SD rats from the following suppliers: Charles River Labs (CRL) International Standard (IS) and Original Standard (OS), Ace Animals, Inc., and Harlan Sprague-Dawley, Inc. The second study assessed individual and group housed ad libitum feeding of Purina Certified Rodent Chow 5002 (20% crude protein), and individually housed controlled feeding of either Purina 5002 or Opti-diet (14% crude protein). The in-life phase of the third study has recently been completed. This study compared controlled (5.5 g Purina 5002 biscuit) to ad libitum (Purina 5002) feeding in CRL IS rats. In the supplier study, survival of male rats was markedly greater for CRL (IS) rats when compared to other groups. Body weight gain and food consumption were greatest in the CRL (OS) rats. Increases in cholesterol, triglycerides, urea nitrogen, and gross renal disease were observed in Harlan and Ace SD rats, while CRL rats had a higher incidence of grossly detectable pituitary masses and foci. In the feeding study, controlled feeding significantly increased the survival rate and decreased body weight gain. Single and group housed SD rats fed ad libitum had decreased T4 and markedly higher cholesterol and triglyceride values, when compared to rats fed controlled diets. Survival of IS rats fed a controlled diet was also notably higher than ad libitum-fed IS rats in the third study.