 Body fat percentage and total body composition will be measured by the air-displacement plethysmography in the PEA POD System and in the iDEXA equipment, using the software for small animals. Based on these measurements of real body fat, predictive models will be adjusted to estimate body fat using the parameters obtained from bioimpedance resistance and reactance and anthropometry Hull et al, 2008, Roggero et al, 2008, Ellis et al, 2008, Ma et al, 2008. 