Working dogs, such as search-and-rescue dogs, need to remain hydrated to safely and effectively perform lifesaving tasks in a variety of environmental conditions. Working dogs and some pet dogs are highly motivated to perform the tasks for which they have been trained. As a result, they may not respond to physiologic signals that drive thirst. Thus, canine handlers need to be responsible for monitoring the health of the dogs and to schedule rest and rehydration. One of the most common conditions affecting dogs responding to disasters is dehydration.1–3 Working dogs may work for extended periods in adverse environments. Similarly, pet dogs may be motivated to endlessly chase a ball or accompany an owner on a run. The handler or owner must know when to allow the dog to rest to optimize safety and performance. One strategy that can be readily performed in a field setting is monitoring the hydration status of a dog. Veterinarians can teach handlers to recognize life-threatening illnesses and injuries and to evaluate vital signs (including heart rate, respiratory rate, body temperature, CRT, and skin turgor) of dogs. The ability of handlers to recognize important signs of illness and perform basic and advanced first aid may make the difference in the ability of a dog to survive or return to work.4
A common sign of dehydration in humans and other animals is an increase in SkTT associated with a decrease in skin turgor. Dehydrated critically ill small animal patients can become hypovolemic as a lower interstitial hydrostatic pressure drives fluid shifts from the intravascular space into the interstitial space.5 Changes in skin pliability (ie, turgor) can be used as an index of body fluid balance because the skin will lose pliability when water balance is negative.6 A sign of dehydration is an increase in the time required for the skin to return to its normal contour. Skin turgor is a common component of hydration assessment in clinical patients. Results of experiments with dogs suggest that clinical signs of dehydration can only be detected after a loss of > 5% BW.7 The location at which skin turgor is monitored may influence sensitivity of the assessment of hydration.
The optimal location for monitoring skin turgor has been evaluated in horses8–10 but is rarely specified in dogs.11 The skin parallel to the sagittal crest (ie, the forehead) of a dog is less likely to be influenced by the degree of subcutaneous fat or body position and represents an area at which there is rapid loss of transepidermal fluid.12 Evaluation of skin turgor on the forehead of a dog is a simple noninvasive method at an easy-to-access anatomic location that may be useful for monitoring a dog's hydration status in clinic or field settings.
Dehydration can also lead to changes in peripheral perfusion variables and a prolonged CRT. When used in conjunction with pulse quality, respiratory effort, heart rate, and mucous membrane color, the CRT can be of use in assessing an animal's blood volume and peripheral perfusion.13 Fluid shifts out of the intravascular space during substantial interstitial dehydration, and intravascular hypovolemia can ensue. Although CRT is not a direct clinical sign of dehydration, a prolonged CRT in combination with increased skin turgor suggests substantial dehydration has resulted in hypovolemia. In a meta-analysis14 of children brought to emergency departments because of vomiting and diarrhea, a prolonged CRT had high specificity (88% to 94%) for identifying children with moderate dehydration (≥ 5%). To the authors’ knowledge, no studies have been conducted on the correlation between CRT and short-term exercise in animals.
The purpose of the study reported here was to evaluate the effect of 15 minutes of exercise on SkTT (as a clinical measure of dehydration) and CRT (as a measure of poor perfusion) in working dogs. Both SkTT and poor perfusion may accompany dehydration with intravascular volume depletion. There is little information for use in identifying clinical signs of dehydration after a 15-minute exercise period in working dogs, a period during which a dog is likely to lose < 5% BW as water. We hypothesized that clinical markers traditionally considered to be predictors of dehydration (eg, skin turgor as measured by SkTT or altered perfusion as measured by CRT) may be useful for predicting mild dehydration after a 15-minute exercise period in working dogs.
Materials and Methods
Animals
Nine exercise-conditioned dogs (4 females and 5 males) of 3 breeds (5 Labrador Retrievers, 3 German Shepherd Dogs, and 1 Golden Retriever) were used in the study. Age of the dogs ranged from 8 to 108 months (median, 50 months). Body weight ranged from 21.2 to 33.0 kg (median, 26.7 kg). Seven dogs were owned by the University of Pennsylvania, and 2 dogs were client owned. Owners of the client-owned dogs provided written consent for participation of their dogs in the study. Study protocols (Nos. 806284 and 806288) were approved by the University of Pennsylvania Institutional Animal Care and Use Committee.
All dogs were in good general health and were exercise conditioned prior to beginning the study. All dogs were enrolled in the PVWDC training program; each dog trained 5 d/wk. Data were collected between June 16, 2017, and June 29, 2017. Dogs were housed in a climate-controlled kennel area before and after exercise.
All dogs were fed 2 or 3 times/d; dogs were fed to maintain an optimal body condition score between 4 and 5 (scale, 1 to 9).15 Dogs were fed various commercial dry kibble dietsa-d throughout the study.
Experimental design and exercise challenge
The study consisted of an 8-day experimental period in which each dog performed the same exercise challenge on days 1 and 8; dogs were under the supervision of a veterinarian during exercise. On the 6 days between exercise challenges, dogs participated in normal training routines at the PVWDC (4 days) and spent unstructured time with foster families (2 days). Food was withheld from all dogs beginning at 10 pm on the night before an exercise challenge; food was provided again after the end of sample and data collection. Dogs had ad libitum access to tap water until they arrived at the PVWDC at approximately 7 am on the day of an exercise challenge.
Each dog was walked on a leash approximately 58 m to an exercise field to initiate an exercise challenge. Each dog completed 15 minutes of continuous exercise, which consisted of 5 minutes of searching on a rubble pile (simulated collapsed building), 5 minutes of agility activities in an agility yard located approximately 20 m from the rubble pile, and another 5 minutes of searching on the rubble pile. Dogs were encouraged to trot from the rubble pile to the agility yard and back to the rubble pile during the transitions. Dogs were allowed to urinate during or after the exercise period; urinations were recorded on a data sheet.
Data collection and recording of variables
Dogs arrived at the PVWDC on the day of an exercise challenge and were placed in the kennel area. After the dogs had a brief acclimation period (approx 10 minutes), initial SkTT, CRT, BW, and core body temperature were recorded. Body temperature was collected by use of an orally ingested sensor and telemetric temperature monitor.16,e Ambient (outdoor) air temperature and relative humidity were obtained from a national weather servicef and recorded at the start of the exercise period. Immediately after the 15-minute exercise period, SkTT, CRT, BW, and core body temperature were measured again.
Dogs were allowed to attain a natural position during measurements, which included standing, sitting, or lying positions. The SkTT was determined by using the thumb and forefinger to elevate a fold of skin lying parallel to the sagittal crest on the parietal bone (ie, forehead of a dog) to a height of approximately 2 cm for approximately 3 seconds (Figure 1).17 The SkTT was defined as the time required for the skin to return to the anatomically normal contour on the head. The SkTT was estimated by 1 of 2 investigators who performed it in a manner that simulated a technique that could be used in a field setting (ie, counting one-one thousand, two-one thousand, three-one thousand, and so forth out loud). A third investigator recorded all SkTT values on a data sheet. The CRT was determined by digital occlusion of the maxilla mucous membranes by means of digital pressure applied for approximately 3 seconds (Figure 2).18 The CRT was defined as the time required for the capillaries to refill with blood and the mucosa to return to the color visible prior to occlusion. The CRT also was estimated by 1 of 2 investigators in the same manner that was used to estimate SkTT. A video camerag and image sensorh were used to record each SkTT and CRT, and video-editing software19,i was used to analyze the recordings after all data were collected. Analysis consisted of quantifying the CRT and SkTT to 0.01 seconds. One investigator analyzed all SkTT and CRT video recordings 3 times, with an interval of at least 12 hours between subsequent analyses. The mean value for the 3 analyses was calculated for SkTT and CRT. After SkTT and CRT were measured, BW was measured to the nearest 0.01 kg on a digital scale.j
Photograph depicting the assessment of skin turgor in exercising dogs, which was performed by using the thumb and forefinger to elevate a fold of skin lying parallel to the sagittal crest on the parietal bone (ie, forehead) of a dog to a height of approximately 2 cm for approximately 3 seconds. The SkTT was the time required for the skin to return to the anatomically normal contour on the head.
Citation: American Journal of Veterinary Research 80, 2; 10.2460/ajvr.80.2.123
Photograph depicting assessment of CRT, which was performed by digital occlusion of the capillaries of the maxillary mucous membrane for approximately 3 seconds. The CRT was defined as the time required for the vessels to refill with blood and return to the mucous membrane color visible prior to occlusion.
Citation: American Journal of Veterinary Research 80, 2; 10.2460/ajvr.80.2.123
Statistical analysis
Data were visually reviewed and tested for normality (Shapiro-Wilk test). Data initially were analyzed by use of a 2-way repeated-measures ANOVA with exercise (before and after exercise) and time (day 1 and day 8) as main effects. The difference in CRT before and after exercise was tested by use of the Wilcoxon signed rank test. Linear regression was performed to identify the relationship between all variables (BW, SkTT, CRT, and core body temperature). A Spearman rank order correlation was used to identify the relationship between data obtained during the study period with video analysis data. Results were considered significant at P ≤ 0.05.
Results
Ambient (outdoor) temperature during the course of the study ranged from 19.4° to 27.7°C (median, 22.7°C). Relative humidity ranged from 58% to 93% (median, 70%). Mean ± SE values for BW, SkTT, and CRT before and after exercise were calculated (Table 1). All dogs urinated before measurement of SkTT, CRT, and BW both before and after exercise.
Mean ± SE values for variables used to assess hydration status before and immediately after a 15-minute exercise period in 9 exercise-conditioned dogs on days 1 and 8 of an 8-day study period.
| P value* | |||||
|---|---|---|---|---|---|
| Variable | Before exercise | After exercise | Time | Exercise | Time × exercise |
| BW (kg) | 27.03 ± 0.90 | 26.97 ± 0.94 | 0.18 | 0.07 | 0.89 |
| SkTT (s)† | |||||
| Manual | 1.74 ± 0.14 | 2.61 ± 0.29 | 0.29 | 0.006 | 0.15 |
| Video | 2.19 ± 0.35 | 3.21 ± 0.43 | 0.56 | 0.05 | 0.22 |
| CRT (s)† | |||||
| Manual | 1.94 ± 0.13 | 1.81 ± 0.14 | 0.72 | 0.51 | 0.30 |
| Video | 2.47 ± 0.21 | 1.86 ± 0.16 | 0.42 | 0.21 | 0.77 |
Time was a comparison between values obtained on day 1 and day 8. Exercise was a comparison of the values obtained before and after a 15-minute period of exercise.
Values were considered significant at P ≤ 0.05.
Manual represents values determined manually during the study by an investigator counting out loud (eg, one one-thousand, two one-thousand, and so forth), and video represents analysis of video recordings performed after all data were collected and was quantified to 0.01 seconds.
Pairs of BW measurements were obtained for the 9 dogs (18 before and 18 after exercise). One BW value for 1 dog was excluded from the analysis because the calculated decrease in BW was 7%, which was considered a measurement error; thus, there were 17 pairs of BW measurements (before and after exercise). There was a detectable, but not significant (P = 0.07), decrease in BW after 15 minutes of exercise for 12 of 17 measurements. Mean ± SE loss of BW after 15 minutes of exercise was 0.83 ± 0.27% (range, 0% to 3.3%).
There was a significant increase in SkTT after exercise determined both as a real-time measure during the experiments (P = 0.006) and when assessed via video review after the experiments (P = 0.05). Linear regression analysis revealed a significant positive relationship (r = 0.68; P < 0.001) between real-time visually observed SkTT and SkTT obtained from video analysis (Figure 3). Mean coefficient of variation for SkTT for the 3 video analyses was 21.22%. In contrast to SkTT, CRT measured in real time or by video review did not differ on the basis of exercise (P = 0.21), time (P = 0.42), or the time-by-exercise interaction (P = 0.30). However, linear regression analysis revealed a significant positive relationship (r = 0.65; P < 0.001) between real-time visually observed CRT and CRT obtained via video analysis. Core body temperature was significantly (P < 0.001) higher after exercise (39.8°C), compared with before exercise (38.4°C); however, there was not a significant relationship between CRT and core temperature.
Results of linear regression analysis of the SkTT (A) and CRT (B) determined manually during the study and during review of video recordings after the study. Each symbol represents results for a working dog (n = 9) determined before and after a 15-minute period of exercise on each of 2 exercise-challenge days. The line of best fit for the data is indicated (dashed line).
Citation: American Journal of Veterinary Research 80, 2; 10.2460/ajvr.80.2.123
Discussion
In the study reported here, SkTT and CRT were evaluated to determine whether skin turgor or CRT (or both) could be useful clinical predictors of dehydration after a 15-minute exercise period in dogs with only mild loss of body water as determined on the basis of loss of BW. In addition to loss of BW, dogs had a prolonged SkTT and an extremely slight, but not significant, decrease in CRT after exercise for 15 minutes. Previously, it was thought that weight loss > 5% was necessary for detection of clinical dehydration, which was an understanding generated from a study6 of resting dogs that did not account for the effect of exercise and did not test SkTT on the forehead. This conservative cutoff for detection of dehydration was based on clinical experience with hospitalized patients and has been accepted, in part, to accommodate variations in BW that are the result of variable quantities of retained urine or feces at the time of BW measurement.11,20,21 Subtle changes in hydration in working dogs may predispose them to heat stress and could impair performance. The authors are aware of no studies that have been conducted to evaluate whether dehydration can be detected at a lower percentage of water loss following exercise in dogs.
The forehead (ie, the area parallel to the sagittal crest on the parietal bone) was chosen as the anatomic location for the SkTT test for multiple reasons. This is an area that does not have excessive amounts of redundant skin that could interfere with the SkTT results. This area is not affected by a dog's posture, which meant that the dogs could sit, stand, or lie without putting substantial tension on the skin over this area during the SkTT test. Also, this area has a higher incidence of transepidermal water loss. In nonexercising Beagles, the head and tail are areas with high water loss.12 Use of a dog's forehead for testing allowed us to take advantage of these characteristics. We were able to perform the test at an anatomic location that was easy for the handler to consistently access and that was already prone to water loss, which made differences in water loss during the 15-minute exercise period clinically apparent. Results of this study suggested that SkTT can be used as a clinical sign to predict small changes in hydration status that develop in a period as brief as 15 minutes, which is a time during which dogs can lose < 5% of BW.
Analysis of results of the present study also suggested that CRT was not an important clinical predictor of mild changes in hydration status after an exercise period of 15 minutes. Peripheral vasoconstriction and a prolonged CRT are physiologically appropriate responses to a low circulating blood volume, which may be a result of severe dehydration with intravascular volume depletion.14 In contrast, the CRT decreased in the dogs of the present study after a 15-minute exercise period. Increases in heart rate and cardiac output and generation of heat during exercise, as indicated by a significant increase in core body temperature after exercise, favor peripheral vasodilation and a shorter CRT. A larger loss of water (as a percentage of BW) is necessary to generate a change in the fluid balance to the point at which intravascular volume can no longer be preserved and vasoconstriction results.
The present study had several limitations. No attempts were made to standardize the SkTT and CRT methods of the 2 investigators who performed the visual SkTT and CRT tests during the data collection period; however, all video recordings were analyzed by 1 investigator. Videos were not always recorded in a manner that made it easy to clearly view the return of the skin to a normal contour because movement of dogs and investigators occurred frequently. The mean coefficient of variation for the 3 video analyses of the SkTT was 21.22%. In a clinical or field setting, a user-friendly version (eg, counting one-one thousand, two-one thousand, and so forth as was performed during data collection in the present study) would be used to count the number of seconds required for the skin to return to a normal contour, so the quantitative method of video analysis would not translate to use in field or clinical settings. It would be important for handlers to identify a consistent method of counting when determining the SkTT and CRT. Use of a stopwatch may yield a more exact value, but it would be difficult for handlers to use one in most field settings. Not all dogs lost BW during the 15-minute exercise period. Precision of the scale, a small number of dogs, a short duration of exercise, and variation among dogs all influenced the results. Most of the dogs had a lower BW after the 15-minute exercise period. It is likely that loss of BW would be greater with an increased duration of exercise, especially in a hot and dusty environment of a collapsed building during a disaster response.
An accurate assessment of hydration status in a working dog is crucial. A major problem for dogs during working and deployment is dehydration.1–3,22 In multiple studies of disaster events, such as the 2014 landslide in Oso, Washington1; the 2010 earthquake in Haiti2; and the attack on the World Trade Center in 2001,3 dehydration has been reported as a major cause of illness during work. Several factors likely contribute to dehydration, including hot and dusty environments, heat emitted from fires, long work hours without adequate breaks for the dogs, and lower water consumption during work. Many dogs working at disaster sites have required treatment in the form of SC administration of fluids.3 An important role for veterinary professionals is to educate dog handlers on strategies for recognizing and, more importantly, preventing dehydration. Because dogs are less likely to drink in the hectic activity of a search location, it is strongly recommended that the dogs be moved away from the site at regular intervals to allow for rest and rehydration.23 The roster for a Federal Emergency Management Agency Urban Search-and-Rescue task force does not include a position for a veterinary medical officer, and other working dogs are likely to be deployed without direct veterinary support. In the absence of a veterinary medical officer, veterinary care of working dogs becomes the responsibility of allied medical professionals and canine handlers.2 Multiple SkTTs measured during rest and while working will allow handlers to recognize a dog's baseline SkTT when hydrated and provide a comparison during work. The positive correlation between the real-time visual SkTT and video-analyzed SkTT suggests that a handler can estimate SkTT in field settings.
Use of the SkTT to determine skin turgor will help handlers (and pet owners) monitor the hydration status of dogs; this will allow them to recognize early signs of dehydration and implement appropriate preventative measures (eg, providing drinking water). Although additional studies are needed to determine the reliability of this method for monitoring dehydration during various types and different durations of exercise, the study reported here indicated that skin turgor, as measured by the SkTT, can be used as a clinical tool to predict small shifts in hydration status after a 15-minute exercise period in working dogs.
Acknowledgments
Supported by Nestlé Purina Research.
The authors thank Patricia Kaynaroglu and Vicki Berkowitz for technical assistance.
ABBREVIATIONS
| BW | Body weight |
| CRT | Capillary refill time |
| PVWDC | Penn Vet Working Dog Center |
| SkTT | Skin tent time |
Footnotes
Purina Pro Plan Sport All Life Stages Performance 30/20 Formula, Nestlé Purina PetCare Co, St Louis, Mo.
Purina Pro Plan Focus Sensitive Skin and Stomach Formula, Nestlé Purina PetCare Co, St Louis, Mo.
Purina Pro Plan Overweight Management Formula, Nestlé Purina PetCare Co, St Louis, Mo.
Nutro Wholesome Essential Lamb & Rice, Mars Inc, McLean, Va.
CorTemp indigestible core body temperature sensor and data recorder, HQInc, Palmetto, Fla.
The Weather Channel. Available at: weather.com. Accessed Jun 16, 2017.
HD Handycam, Sony, New York, NY.
Exmor R CMOS sensor, Sony, New York, NY.
Movavi video editor, version 4, Movavi Software Ltd, St Louis, Mo.
Jorgensen Laboratories Inc, Loveland, Colo.
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