Assessment of olfactory sensitivity in horses using positively conditioned scent

Differences in the ranges and capacities of sensory modalities cause horses to perceive their surroundings differently than humans. To date, the horses' sense of smell has been studied mainly regarding social and reproductive behaviour. The role of olfaction in horse management and use also seems to be of utmost importance. The aim of this study was to determine the response to a scent of different intensities by horses of different sexes and types (warmblood horses vs ponies). The study involved 21 adult mares and geldings, of which 15 subjects learned how to complete the required task and were ultimately able to be tested. The study used the mint scent of different concentrations measured by the number of mint drops added to water. A box containing scented cotton was placed in one crib to allow the horses to perceive the odour. In contrast, another crib, which looked identical but was odourless, was hung in the stall to determine whether horses distinguished which of the cribs contained the scent. The horses were unable to see, touch, or taste the cotton itself. They were positively conditioned to the mint odour and were then schooled to indicate the crib with mint drops. The selected horses, which were capable of indicating the scented crib, were then tested six times for each of four decreasing odour concentrations. During the 30 s observation period, the exploration time, frequency of exploration events, and prevalence of additional behaviours (licking or nibbling on the smelling crib and empty-mouth chewing) were recorded at both cribs. The mint-scented crib was explored more intensively than the empty crib at each scent concentration, and the odour recognition was manifested mainly by a longer exploration time (with decreasing concentration: 11.7 s vs 4.8 s, 12.7 s vs 4.6 s, 12.6 s vs 5.5 s, 11.3 s vs 5.4 s; P < 0.01 and 9.5 s vs 5.7 s; P < 0.05). However, interest in scent decreased with reduced odour concentration. The sex and type of horses rarely differentiated the horses' response to the positively conditioned scent. Thus, the biological traits studied do not significantly affect the olfactory sensitivity of horses. Nevertheless, the study showed that horses' olfactory sensitivity is high, and this sense may be of crucial importance for learning. These findings should be considered in horse management and use.