[Plasma concentrations of thyroid hormones in the domestic goat. Seasonal variations in relation to age]

Plasma thyroid hormones (T3 and T4) were investigated by immunoenzymatic methods in an Umbrian indigenous goat population. Seventy females and 10 males, aging 1 to 14 years, were tested in different periods of the year. Mean values (m +/- SD) of 320 determinations were 2,4 +/- 1,5 ng/ml (ranging from 0,5 to 7,0) for T3 and 6,5 +/- 2,5 micrograms/dl (range 2,2 - 14,2) for T4. The highest values for both hormones were recorded in spring, the lowest at the end of the summer (mean decrease: T3 = 57%; T4 equal 35%). Thyroid hormone levels decreased with age, young animals under 3 years showing higher values and lower summer decreases (particularly of the T3 levels), than mature animals (4 - 8 years old). Old goats, (aging 9 - 14 years) showed the lowest values for both hormones.