Seasonal alterations in plasma β-hydroxybutyrate and related biochemical parameters in the desert tortoise (Gopherus agassizii)

β-Hydroxybutyrate and routine biochemical parameters were determined on plasma and urine samples obtained from free-ranging desert tortoises over a 1-year period. Urea nitrogen varied inversely with total protein concentration (P < 0.019); significant azotemia and hypoproteinemia were noted following emergence from hibernation. In summer, elevated glucose and cholesterol levels, together with lower sodium, urea nitrogen and urine specific gravity, reflected availability of food and water. Plasma β-hydroxybutyrate levels significantly (P < 0.004) increased in the fall (1.92 ± 0.95 mmol/1), during a period of low rainfall. Results suggest that plasma β-hydroxybutyrate may increase in response to short term energy needs, while protein catabolism plays a greater role in providing fuel during hibernation.