Total and free iodothyronines profile in donkey (Equus asinus) over a 12 months period

Several studies show the correlation between thyroid function and reproductive activity in mares, but no data are available in donkeys. The aim of this study was to determine physiological thyroid changes that could occur in 10 pregnant and 14 barren donkeys over a period of 12 months. Blood samples were collected monthly from the jugular vein of pregnant and barren donkeys from June 2008 to June 2009. No significant differences (P < 0.05) of iodothyronine levels were observed between pregnant and barren donkeys in the same month. Seasonal total thyroxine (T4) and free triiodothyronine (fT3) patterns remained unmodified, regardless of physiological state, with the lowest T4 levels at September and the highest at February, and the lowest fT3 levels at June and the highest at July, in both pregnant and barren donkeys. Ranges of total triiodothyronine (T3) levels in pregnant donkeys over a 12 months period ranged from 1.57 to 2.90 nmol/l, T4 from 31.01 to 63.67 nmol/l, fT3 from 3.15 to 15.52 pmol/l and free thyroxine (fT4) from 22.47 to 33.69 pmol/l. Mean T3 levels in barren donkeys over a 12 months period ranged from 1.64 to 3.37 nmol/l, T4 from 42.95 nmol/l and 61.90 nmol/l, fT3 from 3.15 to 11.19 pmol/l and fT4 from 25.46 to 35.06 pmol/l. This is the first study that provided a seasonal thyroid hormonal profile in healthy barren and pregnant donkeys.