EFFECT OF EARLY BODY-WEIGHT AND MODERATE DIETARY RESTRICTION ON THE SURVIVAL OF THE SPRAGUE-DAWLEY RAT

The effects of ad libitum (AL) feeding, moderate dietary restriction ( DR), and initial (6-week) and one-year body weights on the two-year su rvival of the Sprague-Dawley (SD) rat were evaluated. DR-fed rats were given approximately 75 percent of the adult AL food intake. At two ye ars, body weights of DR-fed males and females were approximately 69 an d 58 percent of the AL-fed male and female body weights, respectively. The 2-year survival rate was 80 and 74 percent in DR-fed males and fe males, respectively, and 28 and 38 percent in AL-fed males and females , respectively. This increase in longevity indicates that DR-fed males and females in carcinogenicity studies would have 14.8 and 9.1 additi onal weeks of exposure in a 2-year period to test compounds, respectiv ely, compared to AL-fed animals. There was no correlation between init ial body weight and 2-year survival in DR or AL-fed rats. There was no association between 1-year body weight and 2-year survival among DR-f ed rats. However, AL-fed rats with the greatest 1-year body weight had a lower 2-year average survival compared with the lightest AL-fed rat s; this trend was statistically significant only in males. Body weight s between the first and second years were statistically significantly correlated for both genders and feeding regimens but no correlation wa s observed between pretest and 2-year body weights. These findings dem onstrate that initial body weight is not the determining factor of 2-y ear survival, but that the total adult food (caloric) intake is import ant, In conclusion, moderate dietary restriction prevented excessive b ody weight gain and greatly increased the 2-year survival of the SD ra t. Initial body weights did not correlate to 2-year body weight gain a nd were not a predictive biomarker of 2-year SD rat survival.