Thyroid function in fed and fasted white-tailed deer fawns

Abstract

Serum thyroid hormone concentrations and thyroxine (T4) kinetics were determined in three fed and two fasted white-tailed deer fawns (Odocoileus virginianus borealis). Fasting for 16 days resulted in a drastic decline in total triiodothyronine (T3) (3.22 to 0.49 ng/mL), T4 (241.6 to 68.3 ng/mL) and, to a lesser extent, free T4 (FT4) (2.59 to 1.37 ng/dL). Reverse T3 (rT3) did not change significantly. Although T4 secretion rate (TSR) was greatly reduced (P < 0.05) in the fasted fawns (2.5 (fasted) versus 10.5 (fed) μg T4 per body weight 0.75 (in kilograms) after 20 days of fasting), fractional turnover rate (k/day), total distribution volume (TDV), and metabolic clearance rate (MCR) of injected [131I]T4 did not differ significantly from values in fed fawns. Serum thyroid hormone profiles of the fasted fawns were similar to those reported previously in wild deer collected in Michigan during late winter. In contrast, however, there was no indication of thyroid enlargement.