Development of a novel paradigm for the measurement of olfactory discrimination in dogs (Canis familiaris): A pilot study

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Olfactory dysfunction in older human beings has been shown to be associated with an increased risk of cognitive decline, yet age-related changes in olfactory behavior have received little attention in the dog model of human aging. We developed an odor habituation and fine odor discrimination paradigm to test the hypothesis that dogs would show a novelty response toward unfamiliar urine from entire male conspecifics. We tested 26 odor detection dogs (14 females, 12 males) from the New South Wales police dog unit, ranging in age from 1 year 2 months to 11 years 10 months. First, dogs were familiarized with a master odor over 2 presentations. Second, we measured difference in investigation time of a master odor as compared with 5 odor mixtures using the following ratios of novel-to-master odor: 100:0, 80:20, 60:40, 40:60, and 20:80. Dogs habituated to the master odor after the first presentation (t(25) = 6.048, P < 0.001). After 2 dogs that failed to habituate were excluded, there was a nonsignificant trend (t(21) = −1.968, P = 0.062) for aged dogs (>8 years, N = 6) to show reduced habituation as compared with middle-aged dogs (5-8 years, N = 9) and with all dogs aged <8 years (N = 18, t(21) = −1.883, P = 0.072). Approximately half of the dogs tested (N = 11) failed to show a novelty response toward the 100:0, novel:master odor. The remaining dogs (N = 15) showed a significant novelty response toward this odor (mean difference = 1.89 seconds, confidence interval = 0.86-2.84). Investigation of the remaining odor mixtures was not significantly different from investigation of the master odor in all dogs. Further development of this paradigm is needed using naive pet dogs before it can be used as a reliable measure of fine odor discrimination. The current, weak trend for an age effect in habituation warrants further investigation in a larger cohort to determine if this effect becomes significant or if it is simply a manifestation of small sample size and low statistical power. It is recommended that future studies use dogs that have not been trained against or actively discouraged from investigating urine because previous learning may have had a significant effect on the outcomes of this study.