Thyroid hormones and metabolic rate in burros, Equus asinus, and llamas, Lama glama: Effects of environmental temperature

Abstract 1. 1. Rate of oxygen consumption, V 02 , and thyroid hormones secretion rate were measured in burros, Equus asinus and llamas. Lama glama . exposed to heat, cold and dehydration. 2. 2. The llama had a lower V 02 than the burro. Exposure to heat for 3–4 days and to dehydration decreased V 02 in both species. 3. 3. Plasma levels of T 4 and T 3 were higher in the llama than in the burro. However, secretion rates of T 4 and T 3 were similar in both species. The discrepancy between thyroid hormonal plasma levels and secretion rates in llamas and burros were due to differences in the disappearance rate (K) of these hormones. 4. 4. The difference in V O 2 between the two species does not seem to be related to thyroid function.