Use of a habituation-dishabituation paradigm to assess gilt olfaction and sensitivity to the boar pheromone

Olfactory stimuli have been used to reduce stress in weaning pigs and induce sexual behavior in sows. Despite the importance of olfaction in pig production and behavior, there is no simple method to assess pig olfaction. Thus, the objectives of this study were: (1) to evaluate the use of an olfactory habituation-dishabituation paradigm (H-D) in pigs, (2) assess gilt olfactory sensitivity and discrimination to the boar pheromone and isoamyl acetate (control odor), and (3) develop sample size and statistical power guidelines for this method. Each gilt (N = 10) received six test sessions. Each session consisted of five consecutive presentations of mineral oil (habituating stimulus) and the presentation of the boar pheromone or isoamyl acetate as the dishabituating stimulus diluted in mineral oil. The boar pheromone was presented at different concentrations in ascending order across sessions (0.008-80 ppm). A significant increase in odor investigation in the odorant trial, compared to the last habituation trial, indicated gilts dishabituated from mineral oil and perceived the odorant at the given concentration. Overall, a significant increase in investigation occurred at the pheromone concentration of 0.8 ppm (P = 0.005) and 8 ppm (P = 0.002) and for isoamyl acetate (100 ppm; P = 0.02). The initial behavioral response of most gilts was to the boar pheromone at 0.8 ppm, but two gilts had an initial behavioral response to the boar pheromone at 0.008 ppm and another two at 0.08 ppm. Thus, using this H-D paradigm we were able to identify sensitivity differences to the boar pheromone among gilts. Post-hoc power analyses showed that a statistical power greater than 0.80 at a significance level of 0.05 can be found with a sample size of 9 animals. In conclusion, we found that the H-D paradigm developed in this study may be a useful rapid test to assess pig olfaction without extensive training.