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A series of experiments in Australia have clearly shown that the percentage of estrous gilts displaying the standing- response to the back-pressure test is reduced when gilts are housed adjacent to boars (Figure 1).
The decrease in efficiency of estrous detection is thought to occur because gilts become accustomed (habituated) to auditory and olfactory stimuli of the boar and are then less responsive to boar stimuli at the time of estrous detection. This result may occur because gilts are habituated or are refractory (females are in estrous but will not stand) to boar stimuli at the time of estrous detection.
The following experiment was conducted to test the hypothesis that estrous gilts become refractory to boar stimuli after initially exhibiting standing estrus.