Serum Triiodothyronine (T3) and Thyroxin (T4) Concentrations in Lipizzan Horses

Abstract

âebulj-Kadunc N., M. Kosec, V. Cestnik: Serum Triiodothyronine (T 3 ) and Thyroxin (T 4 ) Concentrations in Lipizzan Horses. Acta Vet. Brno 2003, 72: 17-22. The Lipizzan horses are a breed with a long breeding history that may have developed differences to other breeds in thyroid hormone concentrations. The objectives of this study were to determine the influences of age, sex and pregnancy on total serum triiodothyronine (T3) and thyroxin (T 4 ) levels in Lipizzans and to compare the results with reference values of other horse breeds. T3 and T4 concentrations were determined in blood serum of 131 stallions, 118 mares and 25 foals of the Lipizzan breed by using a radioimmunoassay (RIA), validated for horse serum. The highest thyroid hormone levels were found in foals. The lowest serum T4 values were obtained in animals aged 16 years and more, the lowest T 3 values in the range of 1 to 3 years. At 4 years, T 3 concentrations rose and then steadily declined. In all categories of horses, significantly higher serum T 4 was found in males, but the sex dependent differences of T 3 were less evident. T 3 and T 4 values in pregnant mares were significantly lower (P < 0.01) than in non-pregnant ones and in stallions. In contrast to the data in the literature, a significant decrease of T 4 was observed between the 7 th and 10 th month of pregnancy, while T3 remained almost unchanged. The mean total serum T 3 and T 4 values in Lipizzans were in the normal range for warm-blooded horses and the age and sex-related fluctuations were in agreement with those for other horse breeds. Horse, lipizzan, age, sex, pregnancy, RIA, thyroxin; triiodothyronine.