Body fat at puberty in rats: alteration by changes in diet

The body composition (percent body fat) at vaginal opening of groups of rats fed different diets was determined. Serial changes in body composition prior to vaginal opening were also measured to assess the temporal relationship between first achievement of the body composition subsequently found at puberty and the actual onset of puberty (vaginal opening). The body weight at vaginal opening and the total carcass fat at vaginal opening were significantly different among the three dietary groups (F = 43.06 and 44.60, respectively; P less than 0.001). In addition, the percent body fat at vaginal opening was also significantly different among the three dietary groups (F = 30.30; P less than 0.001). In one group, the percent body fat was the same at the age of 31 days as it was at vaginal opening (mean age 41 days). In a group where food intake was restricted, the percent body fat prior to and at vaginal opening remained lower than that seen at vaginal opening in a group fed the same diet ad libitum. Thus, attainment of a critical level of body weight, total body fat stores, or percent body fat does not trigger puberty in rats.