Summary: Total body composition in live, un-anaesthetized small animals and carcasses will reveal absolute amounts of body fat, lean tissue and body water via a quantitative magnetic resonance (QMR) instrument, EchoMRI, (Echo Medical Systems, LLC, Houston, TX). This instrument uses the differences in the nuclear magnetic resonance properties of hydrogen atoms in organic and non-organic environments to fractionate signals originating from fat, lean tissue and free water.