Abstract. Total serum triiodothyronine (T 3 ) and thyroxine (T,) concentrations were assayed in neonatal llamas from birth to 90 days of age. T 3 concentrations were high at birth and increased from birth to approximately 6 days, then gradually decreased. T 4 concentrations were highest at time of birth and decreased gradually over the 90-day period.Knowledge of baseline serum thyroid hormone concentrations is necessary for the diagnosis and investigation of thyroid-related diseases. Basal serum triiodothyronine (T 3 ) and thyroxine (T 4 ) concentrations for llamas (Llama glama) in North America have only recently been established. 13,30 One study determined serum T 3 and T 4 concentrations in males, females, and pregnant females, ranging in age from 6 months to 10 years. 30 The other study divided test subjects into several age and sex categories, including 1 group with animals less than 1 month old. 13 Research in other species, however, has shown that serum T 3 and T 4 concentrations are highest shortly after birth and decline thereafter for a variable period of time. 9,12,16,17,24 The extremely high hormone concentrations of neonatal animals could cause errors in interpretation if compared with normal values from older animals. An erroneous diagnosis of hyperthyroidism could result from comparing normal neonatal hormone concentrations to lower yet normal concentrations of older animals. Conversely, an animal with congenital hypothyroidism could have low thyroid hormone concentrations that fall within the range of normal values from older animals. Thus, a knowledge of serum T 3 and T 4 concentrations in the immediate perinatal period could be useful information for the investigation of congenital hypothyroidism in the neonatal llama.The objective of this study was to determine basal serum T 3 and T 4 concentrations and T 3 :T 4 ratios in neonatal llamas (crias) and to compare these values with those from older animals. Received for publication July 15, 1992.
208Serum T 3 concentrations were high in the 0-2-day age group (X = 5.13 ng/ml) and increased slightly in the 3-4-day and 5-6-day age groups before decreasing steadily in each age group thereafter (Table 1). Peak mean serum T 3 concentrations of 5.47 ng/ml occurred in the 3-4-day age group. Mean serum T 3 concentrations in the 11-30-day age group (3.27 ng/ml) were only approximately 60% of those in the 3-4-day age
Materials and methodsSpecimen collection. Blood samples were collected from 66 crias of both sexes that appeared vigorous and exhibited normal behavior after birth. Venous blood samples were allowed to clot at 4 C, the samples were centrifuged, and the serum was removed and stored at -20 C until analyzed. The samples were allotted to groups based on the animal's age: 0-2 days, 3-4 days, 5-6 days, 7-8 days, 9-10 days, 11-30 days, 31-90 days.Hormone assays. Total serum T 4 concentrations were determined by use of a radioimmunoassay diagnostic kit. a Total serum T 3 concentrations were determined by use of a microparticle enzyme immunoassay. b The ...
