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Pubertal Food Intake and Body Length, Weight, and Composition in the Feed-Restricted Female Rat: Comparison with Well Fed Animals

Summary: Individual pubertal age, food intake, and body length, weight, and composition were determined by direct measurements in 28 feed-restricted female rats studied from birth to first estrus, and were compared to well fed controls (39). The average birth (6.87 ± 0.19 g) and weaning (49.39 ± 0.72 g) weights of the 13 early maturing feed-restricted rats did not differ significantly from those of the 13 late maturers (6.72 ± 0.31 g and 49.96 ± 1.0 g, respectively). Mean values for all pubertal measurements are included in Table 1. First estrus was simultaneous with vaginal opening in nine (69%) of early and two (15%) of the late maturing feed-restricted rats. At first estrus, the late maturing, feed-restricted animals were heavier, longer (Fig. 1), and had attained a greater quantity of total body fat, protein, and water than the early maturers. Furthermore, at first estrus the late maturing feed-restricted rats had acquired a greater proportion of body water than the early maturers; however, both groups had attained the same proportion of body protein (Fig. 2). Although early and late maturing feed-restricted rats were eating the same amounts of food at the time of vaginal opening and at first estrus, late maturing rats consumed less food per 100 g body wt than did early maturers. The average birth (6.99 ± 0.74 g) and weaning (49.7 ± 0.74 g) weights of all 29 well fed rats did not differ from those of the feed-restricted group (6.76 ± 0.17 g and 48.95 ± 0.6 g, respectively). First estrus was simultaneous with vaginal opening in 20 (69%) of the well fed and 13 (46%) of the feed-restricted rats. At first estrus average body weights and nose-rump length were the same for well fed and feed-restricted groups. Mean ages at vaginal opening and at first estrus in the feed-restricted animals were, however, greater. Absolute amount and percentage of body water did not, on the average, differ in the two groups; however, the feed-restricted animals attained less fat, were proportionately leaner, acquired a greater quantity and proportion of protein, and consumed less food.Speculation: As seen within the previously studied well fed control group, differences in food intake and somatic development in individual feed-restricted rats at first estrus suggest that the attainment of a constant body weight, level of fat, or food intake may not be essential for the onset of puberty. Our findings in rats at first estrus suggest that although dietary manipulation may effect a change in the overall proportion of body fat and protein, within a homogeneous group of rats at first estrus there is a percentage of body protein which remains the same with increasing age at sexual maturation.