Dog sniffing biomechanic responses in an odor detection test of odorants with differing physical properties

Dogs are utilized in forensic science for their extensive scent-detection capabilities. They are often considered the "gold standard" in-field detection for targets such as illicit drugs and explosives. Despite their prevalence in the field, relatively little is known about how dogs interact with and transport volatile organic compounds through their olfactory system. In this study, 2 groups of dogs were utilized-Sport detection dogs (n = 19) that participate in the National Association of Canine Scent Work and have achieved advanced standing through training and successful search competitions and law enforcement explosive detection dogs (n = 8) which were included for comparison. Both groups were presented with 2 target odorants having differing molecular properties, 2-ethyl-1-hexanol and ammonia, 2 non-target odorants, 1-bromooctane and methyl benzoate, and a negative control. Canines were tested prior to experience with the target odorants, when all odorants were novel, after some brief training with the target odorants, and after a longer training time with the target odorants. The non-target odorants were never used in training. Sniffing was measured using flow sensors embedded in a wall immediately in front of the odorants held in a closed cylinder. Sensor data were used to calculate sniff flow rate, frequency (sniffs per seconds), and volume. Results indicated no difference in sniffing dynamics between target odorants; however, sniffing frequency increased significantly with increased experience with the target odorants (Wilcoxon rank sum exact test, W = 148, P = 6 × 10-5). Sniff volume and flow rate showed a positive correlation to body mass for all sport detection dogs (slope = 2.71, F(1,17) = 9.48, P = 0.007, R2 = 0.32), though the R2 was low, indicating other factors at play. Law enforcement detection dogs were shown to take in significantly higher mean total sniff volumes (Wilcoxon rank sum exact test: W = 0. 7, P = 10-4) and volume flow rates (Wilcoxon rank sum exact test: W = 5, P = 6 × 10-5) compared to the sport detection dogs, but the sniff frequency remained similar for both groups.