SEX DIFFERENCE IN OLFACTORY SENSITIVITY TO THE BOAR CHEMOSIGNAL, ANDROSTENONE, IN THE DOMESTIC PIG

Sexually dimorphic responses to chemical stimuli involved in reproduction-related communication are widespread, but the possibility that this dimorphism is caused by differences between the sexes in the ability to smell the olfactory cue has seldom been investigated. Sex differences in the ability of domestic pigs, Sus scrofa, to detect 5α-androst-16-en-3-one (androstenone), a steroid produced by boars that modulates the sexual response of sows, were investigated using an operant task. Five normal adult males and five pregnant adult females were trained to discriminate between an odour and a blank (no odour), opening a reward box in the presence of an odour but not in the presence of a blank. All pigs were tested with control odour (pinene or isoamyl acetate) versus blank, androstenone versus blank, and blank versus blank trials. Sows performed equally well with androstenone and the control odour. While boars matched the performance of sows on the control odour, they initially performed no better on androstenone than on blank versus blank trials, indicating that they could not detect its odour. The performance of four of the five boars improved during repeated testing with feedback. The same pattern of improvement occurred when boars were tested with a concentration of pinene that they were initially unable to discriminate from a blank. These results suggest that the concentration of androstenone used in the study was easily detectable for sows, but initially near or below the detection threshold for boars. Thus, sensitivity to a biologically significant chemical cue is sexually dimorphic in this mammal. © 1991 The Association for the Study of Animal Behaviour.