Evaluation of normal triiodothyronine and tetraiodothyronine concentrations in llamas (Lama glama)

Basal serum triiodothyronine (T3) and tetraiodothyronine (T4) concentrations have not been established for the llama (Lama glama). In addition, changes in T3 and T4 concentrations in response to thyroid-stimulating hormone (TSH) administration have not been determined, making clinical evaluation of problems referable to thyroid dysfunction difficult. In study 1, basal T3 and T4 concentrations were determined in serum samples collected from 132 clinically healthy llamas. The llamas were allotted to 3 groups: mature intact or neutered males (group I, n = 25), nonpregnant sexually mature females (group II, n = 21), and pregnant females (group III, n = 86). A mean concentration and a 95% confidence interval were computed for each group. An analysis of variance (ANOVA) indicated that a single confidence interval range (0.45 to 4.18, mean = 1.37 ng T3/ml) adequately defined the normal T3 concentrations for all groups. An ANOVA indicated that the T4 concentrations for the female populations (groups II and III) could be combined with a normal confidence interval range of 39 to 204 ng/ml (mean = 88 ng/ml), whereas a separate range (70 to 220 ng/ml, mean = 124 ng/ml) was determined for the male population. An ANOVA indicated that a single confidence interval range (0.0066 to 0.0321, mean = 0.0146) adequately defined the normal T3/T4 ratio for all groups. In study 2, T3 and T4 concentrations were evaluated in 10 healthy llamas immediately preceding and at 2, 4, 6, 8, and 24 hours after the IV administration of 3 IU of TSH/44 kg of body weight. The T3 and T4 concentrations were significantly higher by 2 hours after TSH administration in both groups. Peak T3 and T4 concentrations were observed at 4 and 8 hours, respectively, after TSH administration. When normalized with respect to serum T3 concentrations in samples collected immediately prior to TSH administration, the maximal increase in predicted T3 concentration was 4.06-fold (80% confidence interval range = 2.99- to 5.50-fold) at 4 hours after TSH administration. The maximal increase in predicted normalized T4 concentration was 2.32-fold (80% confidence interval range = 1.76- to 3.05-fold) at 8 hours after TSH administration. The TSH-stimulated increases in T3 and T4 concentrations at 4 hours were clearly distinguishable from values in samples obtained before TSH administration.