Comparative Plasma and Urine Chemistry of Fasting White-Tailed Prairie Dogs (Cynomys-Leucurus) and American Martens (Martes-Americana): Representative Fat-Bodied and Lean-Bodied Animals

American martens and white-tailed prairie dogs are mammals of similar body mass, exposed to periods of food deprivation, but of vastly different body fat content. While both species demonstrated a protein conservation phase during a short-term fast, martens had a greater reliance on protein as depicted by greater loss of body weight, higher daily urine volume, and glomerular clearance rates, as well as higher daily urinary urea excretion. Protein use was calculated to be 3.15 and 1.23 g/d for martens and prairie dogs, respectively. Martens did not hydrolyze a greater amount of urea as they were hypothesized to do in order to conserve water. Urinary beta-hydroxybutyrate (BHBA) excretion decreased during the fast in both species but prairie dogs had higher plasma levels of BHBA, which suggests that regulation of protein catabolism may be in part from ketone bodies. By using fat and protein in a ratio of about 2:1, martens may maintain sufficient hydration, extend their fat stores, and retain muscle integrity during short-term fasts.