[Concentrations of testosterone, estrone and estrone sulfate in peripheral blood of donkey stallions in relation to season]. / Jahreszeitlicher Konzentrationsverlauf von Testosteron, Estron und Estronsulfat im peripheren Blut von Eselhengsten.

OBJECTIVE: To assess testicular endocrine function in the male donkey (Equus asinus) during the course of the year. MATERIAL AND METHODS: In 5 miniature and 4 standard donkey stallions, peripheral blood concentrations of testosterone (T), estrone (E1) and estrone sulfate (E1S) were determined using radioimmunoassay. RESULTS: There was a highly significant influence of the season (p < 0.0001) on the course of all 3 steroids. Values were low in November until January and high in April, May and June. As delineated by the measurement of E1 the breed also had an effect on the expression of seasonality. Mean T concentration (X̅g × SF ±â€…1) was 1.58 × 1.20 ±â€…1 ng/ml, values ranged between 0.39 and 5.95 ng/ml, which is approximately double the plasma T concentrations observed in horse stallions. As in horse stallions, E1 levels were only slightly above the detection limit of the assay (0.10-0.17 ng/ml). Mean E1S concentration amounted to 0.91 ±â€…0.23 ng/ml, values ranged between 0.34-1.36 ng/ml and taking peak levels into account measured approximately 300-fold lower than in the horse stallion. CONCLUSIONS: The data obtained confirm that the donkey belongs to the group of long day breeders. Irrespective of the close phylogenetical relationship the course of E1S concentrations reveals distinct differences between horse and donkey. CLINICAL RELEVANCE: Even between closely related species established reference values for sex steroids cannot be transferred without verification.