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Comparison of Three Acute Stressors in Horses
Stress in horses can be caused by any number of things: a new pasture mate, trailer ride, unexpected loud noise, or even strenuous exercise. The objective of this study was to test three stressors (air horn, firecracker, and exercise), to determine their effect on heart rate (HR) and time from elevated heart rate to return to baseline heart rate. A total of 6 horses were used in this study; 3 mares, 2 fillies, and 1 gelding. The horses were used in a crossover design over a two month period where each horse received each stressor every 7 days. The horses remained in a stall while the Pre-Stress HR was measured every 30 sec for 5 min to determine baseline. Once baseline was established, the horse was brought to a round pen and exposed to a specific stressor. The exercise stressor required the horse to trot or canter for 10 minutes; 5 min clockwise and 5 min counter-clockwise. The air horn and firecracker stressors lasted between 5 to 10 sec during each exposure. Immediately following being exposed to the stressor, the Stressed HR was recorded every 30 sec for 90 sec. The horse was then returned to original stall and the Post-Stress HR was recorded every 30 sec for 15 min. Statistical differences in treatments were determined using the Proc GLM in SAS. There were no differences between the mean Pre-Stress HR of each of the stressors. The mean Stressed HR for the air horn (89±14) was significantly higher (P<0.06) than firecracker (58±5) but not different from exercise (72±4). There was no significant difference among the stressors’ Post-Stress HR means. At the immediate Stressed HR measure, the one with the greatest effect (P<0.03) on HR was the air horn (109±19) compared with exercise (77±4) and the firecracker treatment (66±5). At the second immediate Stressed HR measure (60 s following end of stimulus) there was HR was not different between the air horn (86±14) and exercise (71±4) but both were greater (P<0.07) than firecracker (57±5). There were no differences in the mean Post-stressed HR between treatments. These results indicated that the short-term use of an air horn will elevate a horses HR greater than 10 min of exercise but only for a short duration. Also, the use of a firecracker to induce short-term stress is not effective.
Keywords: horse, stress, heart rate, air horn, stressors