Effect of sexual stimulation on concentrations of 5α-androstenone and testosterone in the peripheral plasma of boars reared individually

Six Yorkshire boars were reared from 107 days of age in individual pens. No female pigs were housed in the same building. When the boars were 200 days old, sows in oestrus were introduced to the pens of five boars and remained with the boars for 2 days. No oestrous sow was introduced to the pen with the sixth boar. Plasma 5α-androstenone and testosterone concentrations were low between 107 and 200 days of age in all boars. The maximum mean concentrations of these two steroids during this period were 6.18 ± 0.72 and 3.04 ± 1.02 ng/ml, respectively. Plasma 5α-androstenone concentrations increased with advancing age (P < 0.01). A similar trend was not seen for plasma testosterone concentrations. Plasma concentrations of 5α-androstenone and testosterone increased by 247 ± 27% (P < 0.02) and 1212 ± 204% (P < 0.001), respectively, in the samples drawn 24 h after the introduction of the sexually receptive sows. The maximal mean concentrations recorded following sexual stimulation were 12.90 ± 1.80 and 17.51 ± 1.96 ng/ml for 5α-androstenone and testosterone, respectively. The control boar also showed increases in plasma 5α-androstenone (221%) and testosterone (751%) concentrations in the same period, probably in response to auditory and olfactory stimuli originating in the pens nearby with introduced oestrous sows.