Detection of oestrus in gilts housed adjacent or opposite boars or exposed to exogenous boar stimuli

Abstract

This study investigated the influence of continuous exposure of gilts to exogenuous auditory and olfactory stimuli from boars on efficiency of detection of oestrus using the back-pressure test (BPT). The experiment was a 4×4 Latin square design with 12-month-old gilts housed in four groups of 6 animals. Gilts were housed either opposite to boars, separated by a 1-m-wide corridor (Opposite); adjacent to boars, separated by a wire mesh wall (Adjacent); isolated from boars and continuously exposed to boar pheromones (3α-androstenol and 5α-androstenone) for 5 min every 25 min for 8 h (Olfactory); or isolated from boars and concurrently exposed to the pheromones and a broadcast of the boar “courting song” (Auditory and Olfactory). The pheromones were delivered by an infusion pump to the back of an ovariectomized sow kept in a stall in the pen with the gilts. All gilts were checked daily for oestrus using the BPT. Following this, the level of proceptive behaviour of the gilts was quantified in a 3 min test which involved recording the amount of time that the gilts spent within 1 m of an adjacent pen containing a mature boar. A lower ( P < 0.05) proportion of gilts were detected in oestrus in the Adjacent treatment (75%) than in the other three treatments and there were no differences in the proportion of gilts detected in oestrus between the Opposite (95.8%), Olfactory (100%) and Auditory and Olfactory (100%) treatments. For the gilts in all treatments there was a peak in the level of proceptive behaviour (attraction to the boar) that coincided with oestrus or expected oestrus and there were rapid changes in this level before and after oestrus. There were no significant differences between levels of proceptive behaviour of the gilts in the Opposite, Auditory and Olfactory and Olfactory treatments and the levels of proceptive behaviour of the gilts in these treatments were significantly higher ( P < 0.05) than the gilts in the Adjacent treatment during oestrus. These results confirm the proposal that continuously housing gilts adjacent to boars separated by a wire mesh wall allows the gilts to habituate to the boar stimuli that facilitate the standing response to the BPT. Consequently, the efficiency of oestrus detection using the BPT is reduced compared with gilts housed opposite to boars or in isolation from boars. It also appears that housing gilts so that they receive constant stimulation from boars also reduces the level of proceptive behaviour of the gilts. Exposure of gilts to exogenous boar stimuli did not influence their sexual behaviour, possibly because the stimuli were not the appropriate stimuli, the stimuli were not applied for a sufficient duration and/or intensity, or because the presence of the boar may be necessary for gilts to habituate to these stimuli.