Seasonal effect on steroids in blood plasma and seminal plasma of boars

Abstract

Unconjugated testosterone (T), 5a-androst-16-en-3-one (Δ-16), dihydrotestosterone (DHT), unconjugated (u Oe) and conjugated oestrogens (c Oe) were determined weekly in the peripheral blood plasma and seminal plasma of 8 boars for a period of 15 months. Four of the boars were kept under natural daylength fluctuations (8–17 h), and 4 boars on a light programme which shifted these fluctuations by half a year. In peripheral plasma of all boars the highest concentrations were found for c Oe (17 ng/ml) followed by Δ-16 (7.3), T (2.2) DHT (0.75) and u Oe (0.24). In seminal plasma of all boars (with an average volume of 172 ml) the highest concentrations were again found for c Oe (5.9 ng/ml) followed by Δ-16 (1.1), u Oe (0.73), T (0.28) and DHT (0.1). This shows that u Oe reach higher concentrations in seminal plasma than in blood plasma. In boars under the influence of natural daylight steroids fluctuated with season. Maximum concentrations were present from October till December. Minimum concentrations were about 1 10 of the maximum concentrations. All steroids measured in blood and semen were similarly affected and all were highly correlated. In boars on an artificial light programme the off-season depression during the summer was completely restored. This indicates that daylight fluctuations are the main reason for seasonal changes of testicular function in the domestic boar.