A Randomized Cross-Over Study Comparing Cooling Methods for Exercise-Induced Hyperthermia in Working Dogs in Training

Abstract

Working dogs are at a high risk of canine non-pyrogenic hyperthermia, a life-threatening condition that can occur due to physical exertion or environmental factors that inhibit dogs' ability to cool themselves. Two frequently recommended cooling methods to reduce body temperature are water immersion and the application of isopropyl alcohol to paw pads. This cross-over study compared the relative efficacy of these methods in 12 working-dogs-in-training with post-exertional heat stress. On each study day, dogs had a physical exam and performed a warm-up exercise followed by sequential recalls in which dogs ran approximately 25 m between two designated handlers for 10 min until they showed multiple signs of heat stress or their core temperature reached 105 °F (40.6 °C). Dogs' temperature and heart rate were collected after each recall. Dogs completed three study days, and each day, randomly received one of three interventions: passive cooling (no intervention), partial water immersion, or isopropyl alcohol. Post-intervention dogs rested for 20 min. Partial water immersion and isopropyl alcohol both cooled dogs more than no intervention, and water immersion cooled dogs more efficiently than isopropyl alcohol. Additionally, the application of isopropyl alcohol raised dogs' heart rates more than water immersion or no intervention, suggesting that the process of applying isopropyl alcohol is potentially stressful to dogs. Thus, partial water immersion is preferred to cool dogs post-exertion due to its more efficient cooling and better tolerance of use.

Keywords: cooling; exercise; heat stress; hyperthermia; isopropyl alcohol; water immersion; working canine.

Figure 1

Set up of recall test. The dog is wearing a heart rate monitor on a band around their torso. The handler releases the dog to sprint back and forth between them and a secondary handler. Another person collects the dog’s temperature and monitors for signs of heat stress.

Figure 2

Effect of cooling intervention on core body temperature over time, beginning post-exertion. This graph shows the effect of the three different cooling interventions (isopropyl alcohol application, passive cooling, and partial water immersion) on dogs’ temperature in Fahrenheit over time. This graph begins at the point after dogs completed recalls (Minute 1 post-exertion). The dogs then received a 30-s cooling intervention, and their temperature was measured again (Minute 2 post-exertion). The dogs completed their assigned cooling intervention and were placed in a wire cooling crate, where their temperature was measured every minute for 20 min.

Figure 3

Effect of cooling intervention on heart rate over time, beginning post-cooling intervention. This graph shows the effect of the three different cooling interventions (isopropyl alcohol application, passive cooling, and partial water immersion) on dogs’ heart rates in beats per minute over time. Due to an error in the heart rate monitors, heart rate monitoring began when the dogs were placed in the wire cooling crate for 20 min rather than immediately post-exertion (this point in time is 3 min post-exertion). As such, heart rate was tracked for 20 min beginning 3 min post-exertion rather than the 22 min of temperature tracking beginning immediately after post-exertion seen in Figure 2. In the wire cooling crate, heart rate was measured every second for 20 min; for visual clarity, this graph shows heart rate averaged over 1 min intervals. Statistical analyses were carried out using the full set of data.