Sled Dog Race Research Articles

Serum Biochemistry and Haematology Alterations in Sled Dogs Before and After a Race

Abstract Long-distance sled dogs are known for their great endurance and ability to run several hundred kilometres over the course of a few days. There are several factors to consider when selecting a team of high-performing sled dogs, including their physique, body score condition, appetite, paws, and ability to adapt to unknown environments and situations. The most common breed used in sled dog racing, Alaska Huskies, are known for their great work diligence, and determined mindset. It has previously been researched how well these dogs endure such intense physical activity using observation of behavioural patterns, physical examinations, and the analysis of alterations in blood parameters. This study aimed to evaluate serum chemistry and haematology alterations in dogs before and after completing a 300 km race in Norway. Changes were observed in haematology and serum chemistry between pre- and post-race blood sampling. Significant increases were observed in the white blood cell count, haemoglobin in blood and creatine phosphokine activity in serum (CK), and significant decreases were seen in the electrolytes (e.g., chlorides, potassium), cholesterol levels, liver (e.g., alkaline phosphatase) and pancreatic enzymes (α-amylase, lipase), and total red blood cell count. Several other parameters were measured, and resulted in insignificant changes. Our results indicated that long-distance racing, in fact, has an impact on the physiology of the dog, influencing muscular system, the gastrointestinal tract, electrolyte balance and haematopoiesis among others.

Evaluating injuries and illnesses that occurred during the Yukon Quest International sled dog race, 2018-2020.

The purpose of this study was to evaluate medical record data from the 2018-2020 Yukon Quest International Sled Dog race to examine injury patterns and risk factors for dogs competing in multi-day ultra-endurance events. Specifically, we summarized injuries and illnesses that resulted in canine athletes being removed ("dropped") from competition, and in orthopedic injuries diagnosed in both dropped and finished dogs. The records of 989 dogs that started the race were examined, but only records from dogs in teams that went on to finish the race were included, for a total of 711 records. Three hundred and sixty five dogs (51.3%) were noted to have at least one abnormal finding in their veterinary medical record during the race. Orthopedic injuries were most common, and 291 injuries were ultimately diagnosed in 234 dogs (32.9%). Ultimately, 206 dogs (29%) were dropped from competition, for any reason. The most common reasons for dropping dogs were orthopedic injuries (156 dogs; 188 injuries), gastrointestinal illness (22 dogs), and cardiorespiratory disease (7 dogs). Most orthopedic injuries in dropped dogs occurred in the thoracic limb (n = 121 dogs; 151 injuries). Of those, injuries to the shoulder were most common (n = 77), followed by injuries to the carpus (n = 59), and injury to the pelvic limb (n = 32). Carpal injuries were the most prevalent injury diagnosed in dogs that went on to finish the race (71 of 85 injuries). Carpal injuries were the most prevalent injuries overall in 2018 (51%) and 2019 (52%). In 2020, shoulder injuries were most prevalent (27%), suggesting that trail conditions may have differed between years. The majority of dogs with an orthopedic injury ultimately were removed from competition (156 of 234, or 66.6%), but the likelihood of finishing the race with an injury depended on the type of injury sustained; 71 of 130 dogs (54.6%) with a carpal injury went on to finish the race, whereas only 9 of 86 dogs with a shoulder injury (10.5%) went on to finish. The results of this study can assist mushers and veterinarians in preparing for races, and in decision making during endurance sled dog races.

Serum myostatin decreases in exercising and aging Alaskan sled dogs, while growth and differentiation factor 15 remains unaltered.

To evaluate the serum concentrations of myostatin and growth and differentiation factor 15 (GDF-15) in Alaskan Husky sled dogs participating in a 350-mile (560-km) race and in an older population, and to examine correlations between changes in serum concentrations and body condition scores (BCSs). Dogs were recruited from 3 teams of Alaskan Huskies participating in the Alaskan-Yukon Quest sled-dog race and retirees from a research sled-dog colony. Serum samples and BCSs were collected prior to racing, midway, and postrace; and in an older cohort (13 to 14 years). Myostatin and GDF-15 concentrations were assessed using commercially available ELISA kits. The median myostatin prerace concentration (9,519 pg/mL) was significantly greater than the mid- and postrace concentrations (7,709 pg/mL and 3,247 pg/mL, respectively). The prerace concentration was also significantly greater than that of the retired sled group dogs at 6,134 pg/mL. GDF-15 median serum concentrations did not change significantly across any racing time point (approx 350 pg/mL) or in the older cohort. No significant correlations were observed between changes in BCS and myostatin or GDF-15 concentrations. Serum myostatin decreases dramatically, yet no correlations to loss of BCS could be found. Myostatin signaling may be involved in maintaining hypertrophic signaling during intense exercise. Neither racing distance nor geriatric/retirement status appears to have an effect on serum GDF-15 concentration. Myostatin was less in the older, retired sled dogs compared to the younger racing cohort. Such differences highlight the roles that fitness level and age play regarding myostatin levels.

Illness Incidence, Psychological Characteristics, and Sleep in Dogsled Drivers During the Iditarod Trail Sled Dog Race.

Every March, dogsled drivers (mushers) compete in a 1569-km race across Alaska, involving physical exertion, mental exertion, and sleep deprivation for up to 2 wk. These factors may increase mushers' vulnerability to illness, making them a relevant study population for acute infection risk factors. Specifically, the influence of psychological factors on illness risk during prolonged physical exertion has rarely been investigated. The aim of this study was to examine the relationship between psychological characteristics, sleep deprivation, and illness incidence in Iditarod mushers. Fourteen mushers completed 4 psychological instruments to assess state and trait anxiety, resilience and perceived stress, and self-reported upper respiratory symptoms (URS) in the month before the race. Mushers self-reported sleep duration and URS during the race. State and trait anxiety, resilience, and perceived stress did not differ between mushers with and without pre- and in-race URS (P>0.05). However, all mushers who reported in-race URS had reported URS ≤9 d before the race, and the onset of symptoms during the race typically occurred shortly after a rest period. Sleep duration was higher in mushers who reported in-race URS, both before (4.9±0.3 h, P=0.016) and during illness (5.9±1.3 h, P=0.006), vs mushers without in-race URS (3.4±0.8 h). This study highlights recent illness, rest periods, and greater sleep requirements as potential risk factors for URS onset during a multiday endurance challenge, whereas psychological factors were not associated with URS.

David W. Schindler—Icon and Iconoclast

David W. Schindler—Icon and Iconoclast

The effect of age and sex on selected hematologic and serum biochemical analytes in 4,804 elite endurance-trained sled dogs participating in the Iditarod Trail Sled Dog Race pre-race examination program.

Endurance-trained sled dogs provide a unique translational model to characterize changes in hematologic and serum biochemical analytes due to the aging process. The primary objective of this study was to determine the effect of age and sex on specific hematologic and serum biochemical parameters in the endurance trained sled dog. Longitudinal and cross-sectional data were analyzed from 9,746 blood and serum samples from 4,804 dogs collected over 7 years as part of the Iditarod Trail Sled Dog Race pre-race examination program. Mixed models analysis was used for statistical analysis and P < 0.01 was considered significant. Dogs ranged from 1–12 years of age and 39% were female. Serum total calcium and phosphorus concentrations and white blood cell count decreased nonlinearly to asymptotic values by 6.6, 3.1, and 6.9 years of age, respectively, equivalent to estimated physiologic ages in human years of 44, 27, and 46 years. Serum glucose concentrations reached their lowest value at 7.8 years of age, equivalent to an estimated human physiologic age of 50 years, after which time the concentration increased. Serum globulin concentrations increased with age, but nonlinearly for females and linearly for males. Most sex-related differences were <5%; however, females had lower serum urea nitrogen (14.7%) and creatinine (7.3%) concentrations, lower serum alanine aminotransferase activity (16.6%), and higher serum total bilirubin concentration (12.8%) and platelet count (6.0%). The endurance-trained sled dog provides an excellent model to separate the physiologic effects of age from those of a sedentary lifestyle on hematologic and serum biochemical analytes.

Effects of dietary supplementation with krill meal on serum pro-inflammatory markers after the Iditarod sled dog race

A seafood-based supplement from krill, rich in omega-3 phospholipids and proteins was tested on a group of dogs competing in the 2016 Iditarod dog sled race to investigate the effects of krill meal on exercise-induced inflammation and muscle damage in comparison to a control group.A single team of 16 dogs received 8% krill meal for 5 weeks prior to the start of race, while another team of 16 dogs received no supplementation. Ten dogs of the treatment and 11 dogs of the control group finished the race and their blood was analyzed for omega-3 index, inflammation (CRP) and muscle damage (CK).The omega-3 index of the krill meal-fed dogs was significantly higher at the beginning of the race (mean 6.2% in the supplemented vs 5.2% in the control group, p < .001). CRP concentrations increased from 7.05 ± 2.27 to 37.04 ± 9.16 μg/ml in the control and from 4.26 ± 0.69 to 16.56 ± 3.03 μg/ml in the treatment group, with a significant difference between the groups (p < .001). CK activity was increased from 90.75 ± 8.15 IU/l to 715.90 ± 218.9 IU/l in the control group and from 99.55 ± 12.15 to 515.69 ± 98.98 in the supplemented group, but there were no differences between groups (p = .266). The results showed that krill meal supplementation led to significantly higher omega-3 index, which correlated with lower inflammation and a tendency for reduced muscle damage after this long-distance sled dog competition. However, these results need to be confirmed by more controlled studies, since it was a field study and effects of race speed or other performance-related factors such as fitness and musher skill on the results cannot be excluded.

Serum Biochemistry and Inflammatory Cytokines in Racing Endurance Sled Dogs With and Without Rhabdomyolysis.

Serum muscle enzymes in endurance sled dogs peak within 2–4 days of racing. The object of this study was to compare mid-race serum chemistry profiles, select hormones, markers of inflammation, and the acute phase response in dogs that successfully completed half of the 2015 Yukon Quest sled dog race to their pre-racing samples (n = 14), as well as mid-race samples of successful dogs to those who developed clinical exertional rhabdomyolysis (ER) (n = 5). Concentrations of serum phosphorus in ER dogs were significantly elevated compared to healthy dogs (median 5.5 vs. 4.25 mg/dL, P < 0.01) at mid race. ALT, AST, and CK show a significant increase from pre-race baseline to mid-race chemistries (P < 0.01), with more pronounced increases in dogs with ER compared to healthy racing dogs (CK- median 46,125 vs. 1,743 U/L; P < 0.01). Potassium concentrations were significantly decreased from pre-race baselines in all dogs (median 5.1 vs. 4.5 mEq/L; P < 0.01), and even lower in dogs with ER (median 3.5 mEq/L; P < 0.01) mid-race. No changes in serum pro-inflammatory cytokine concentrations were noted in any groups of dogs. C-reactive protein was elevated in both groups of dogs, but significantly higher in those with ER compared with healthy dogs mid-race (median 308 vs. 164 ug/mL; P < 0.01). Healthy dogs may have CK elevations over 10,000 U/L, and dogs with ER were over 30,000 U/L. Although potassium decreases in healthy endurance sled dogs during racing, it remains in the normal laboratory reference range; however ER dog potassium levels drop further to the point of hypokalemia. Lastly increases in CRP may be reflective of a physiological response to exercise over the course of a race; however high CRP in ER dogs may be capturing an early acute phase response.

Serum myoglobin, creatine kinase, and cell-free DNA in endurance sled dogs and sled dogs with clinical rhabdomyolysis.

To evaluate whether cell-free DNA (cfDNA) concentrations are increased in dogs with exertional rhabdomyolysis and whether concentrations are correlated with serum myoglobin concentration and creatine kinase activity. Observational cohort study. Yukon Quest 1,000-mile International Sled Dog Race 2015. Twelve normal competitive sled dogs; 5 dogs with rhabdomyolysis. None. Blood was collected from all confirmed cases of exertional rhabdomyolysis and compared to the winning team at the midrace point. Results indicate that median cfDNA did not increase, but decreased by the race finish (prerace=314.2ng/mL versus midrace=283.7ng/mL versus postrace=249.5ng/mL). There were no rises in median cfDNA in dogs with rhabdomyolysis (255ng/mL) negating its potential utility as a measure of acute skeletal muscle compromise. In contrast, myoglobin concentration and creatine kinase activity at the midrace point for normal dogs were significantly lower than dogs with rhabdomyolysis. Values for myoglobin and creatine kinase were strongly positively correlated (R=0.91). cfDNA is not a useful biomarker for exertional rhabdomyolysis in contrast to myoglobin and creatine kinase. Further evaluation of timing and clinical signs suggests that exertional rhabdomyolysis occurs early in endurance activities. Among the dogs with rhabdomyolysis, the dog that demonstrated clinical signs had the highest serum creatine kinase activity and myoglobin concentration.

Mitochondrial respiration in highly aerobic canines in the non-raced state and after a 1600-km sled dog race.

At the annual Iditarod Race, Alaskan Huskies repeatedly run for up to 8 hours at 16 km/h to complete 1600 km. We previously demonstrated high rates of mitochondrial protein synthesis in Alaskan Huskies, which we suspected allowed rapid remodeling of mitochondrial proteins in response to energetic stress. The purpose of this study was to examine mitochondrial respiration in permeabilized skeletal muscle fibers of Alaskan Huskies in the offseason (Non-raced) and following the 1600 km Iditarod Sled Dog Race (Raced). We hypothesized that compared to Non-raced Huskies, raced Huskies that completed a 1600 km race would have greater mitochondrial respiratory capacities, and improvements in capacities of oxidative phosphorylation (OXPHOS) based on NADH-generating substrates as compared to fatty acids. Using high-resolution respirometry (HRR) we investigated the respiration of permeabilized muscle fibers from Alaskan Huskies. Maximum capacities were 254±26 pmol.s-1.mg-1 for OXPHOS (coupled, P) and 254±37 pmol.s-1.mg-1 for the electron transfer system (ETS; non-coupled, E). After racing respiratory capacities from NADH-linked substrates, but not fat-derived substrates increased. Finally, the OXPHOS to ETS capacity ratio (P/E) increased after racing from 0.90±0.03 to 0.97±0.02. From our previous studies and the current study, we conclude that Alaskan Huskies maintain high mitochondrial protein turnover to facilitate rapid adaptation to environmental extremes and energetic challenges.

Insulin-Like Growth Factor-1 and Selected Insulin-Like Growth Factor Binding Protein Concentrations during an Ultramarathon Sled Dog Race.

The objective of this study was to investigate the effects of running a 1000-mile (1600 km) endurance sled dog race on serum insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins 1 and 3 (IGFBP-1 and IGFBP-3). Serum was examined from 12 sled dogs prior to the race, at midrace (approximately 690 km), and again at the finish. IGF-1, IGFBP-1, and IGFBP-3 were assessed using radioimmunoassay or enzyme linked immune-absorbance assays. Mean prerace concentrations were significantly higher than midrace and end-race concentrations at 215.93 ± 80.51 ng/mL, 54.29 ± 25.45 ng/mL, and 55.53 ± 28.25 ng/mL, respectively (P < 0.001). Mean IGFBP-1 concentrations were not different across these time periods at 24.1 ± 15.8 ng/mL, 25.7 ± 14.0 ng/mL, and 26.6 ± 17.6 ng/mL, respectively. IGFBP-3 concentrations showed a modest significant decrease across time periods at 3,067 ± 2,792 ng/mL, 2,626 ± 2,310 ng/mL, and 2,331 ± 2,301 ng/mL, respectively (P < 0.01). Endurance sled dogs show a precipitous drop in serum IGF-1 concentrations. These differences may be related to fuel utilization and excessive negative energy balance associated with the loss of body condition during racing. The relative stability of IGFBP-1 and IGFBP-3 suggests that IGF-1 anabolic signaling is diminished during ultramarathon racing. Further studies comparing the influence of time and duration of exercise versus negative energy balance on serum IGF-1 status are warranted to better understand exercise versus negative energy balance differences.

Effect of pre-exercise massage on exercise-induced muscle injury in sled dogs

Previous necropsy studies have shown that up to 60% of sled dogs competing in endurance sled dog races have areas of muscle damage. Human athletes and trainers have maintained a strong belief, based mostly on personal experiences, that massage can be effective for pre-race preparation and expedited recovery between consecutive events. We proposed that massage could lessen the degree of creatine phosphokinase (CPK) release when utilised prior to endurance activities. A randomised crossover study was performed using minimally conditioned sled dogs from a sled dog racing kennel. Each dog in the treatment group received a 14 min massage immediately prior to controlled endurance exercise. The pre-exercise CPK activity was 64±11 IU/l (mean ± standard deviation). The difference between pre-exercise CPK and post-exercise CPK for both groups was expressed as delta CPK. The delta CPK for the massage group was 62±22 IU/l and 74±55 IU/l for the control group. There was no significant change in concentration of CPK between pre- and post-exercise in the treatment and control group (P=0.2282). The lack of a significant difference between the control and massage group suggests that pre-exercise massage may not reduce the severity of exercise-induced muscle damage.

A survey on orthopedic injuries during a marathon sled dog race.

PurposeThis prospective observational study aimed to describe and quantify orthopedic injuries (OI) during a marathon sled dog race that led to discontinuation of racing (dropped dogs [DDs]) and to suggest potential associations with risk factors during the event.Study designProspective observational study.AnimalsA total of 989 Nordic breed endurance sled dogs that participated in the 2011 Iditarod Sled Dog Race. Data were collected via an extensive questionnaire, medical records, and speed calculations based on Global Positioning System equipment on each dog sled. OI risk factors and DD incidence were statistically analyzed on dogs and teams completing at least half the race distance, including Student’s t-test, Pearson’s chi-squared test, Poisson regression, and various frailty analysis models as indicated. Significance was set at P<0.10 for inclusion in the models with trends established at P≤0.10 and significance declared at P<0.05.ResultsQuestionnaire response was 40.3%. DD incidence was 38.3%, most often due to OI (50.6%). OI occurred most frequently in the thoracic limb (43.3%) compared with pelvic limb injuries (7.3%). Increased speed was associated with fewer shoulder injuries (Ratio=0.65, P=0.03). Carpal injuries were positively related with increased conditioning distance (defined as training miles; Hazard ratio =1.61, P=0.02). The risk to become a DD decreased with every year of increased age of the dogs (Hazard ratio =0.92, P=0.03).ConclusionOI, specifically of the shoulder and carpus, are common in marathon sled dogs. Injury risk may be speed-related and decreases with increasing age of the dog. Further study of environmental, dietary, and trail conditions in sled dog racing orthopedic research is needed.

Injury and illness sustained by human competitors in the 2010 Iditarod Sled Dog Race

ObjectiveAlaska's 1049-mile Iditarod Trail Sled Dog Race is the world's longest sled dog race and the flagship event in the sport of sled dog racing. Race conditions are typically harsh. Physicians are not officially enlisted to care for human competitors. Instead, medical needs are met through an informal system of volunteers, local health care providers, and a fleet of bush planes. The goals of this study were to identify the types of human injury and illness experienced and the methods by which these conditions are treated. MethodsCompetitors in the 2010 Iditarod were surveyed at the halfway point and at the finish of the race. Survey elements included specific types and frequencies of injuries and illnesses, and the sources and types of treatments. ResultsSeventy-one teams entered the race, 62 participated in the halfway point survey, and 55 completed the finish line survey. Ninety-nine injuries were reported by 42 (68%) of the survey respondents. Frostbite was the most common injury, occurring in 20 (31%) of the respondents. Musculoskeletal pain was also commonly reported. Two mushers sustained closed head injuries, with 1 requiring evacuation. Twenty-three mushers (37%) reported an acute nontraumatic condition, most frequently an upper respiratory infection (9 respondents). In most instances, medical conditions were self-managed. Race veterinarians and support staff, as well as local village clinicians, administered the majority of care, typically wound care or oral antibiotic administration. ConclusionsMost injuries and illnesses sustained by mushers in the Iditarod are minor and self-treatable. Life-threatening conditions are rare, and the need for an organized medical care system seems low.

The Effects of Low Intensity Endurance Activity on Various Physiological Parameters and Exercise Induced Oxidative Stress in Dogs

The study of canine athlete physiology has focused on endurance sled dog racing and high intensity short duration Greyhound racing, yet the number of dogs competing in low intensity endurance activities is rising due to the increased numbers of hunting and companion dog activities. There is little information on the physiological effect of longer duration low intensity endurance activities. We set out to evaluate the serum biochemistry, oxidative stress, and cortisol response before and after two consecutive days of exercise in ten healthy unconditioned male dogs. Exercise sessions consisted of 120 minutes on an exercise wheel at 11 km/hour on 2 consecutive days. Blood was collected at four time points: 24 hours pre-exercise (sample 1, Day 0, resting); 2 min post-exercise on days 1 and 2, (samples 2 and 3, respectively); and 20 hours post-exercise, collected on day 3(sample 4). Hematocrit, blood gases, serum chemistry, uric acid, cortisol, and F2-isoprostanes were determined. Serum biochemistry and hematocrit suggested hemoconcentration, mild muscle damage and respiratory alkalosis during exercise, which was expected in the unconditioned canine athlete. In addition, plasma indices of oxidative damage (F2-isoprostanes) increased, as did plasma uric acid (an endogenous antioxidant). Importantly, similar to human studies, plasma F2-isoprostanes decreased 24 hours after exercise suggesting a protective effect of exercise. Serum cortisol concentrations were also markedly elevated at the end of exercise on both days suggesting that timing of sampling may play a role in interpreting cortisol results when looking at previous field studies.

Influence of endurance exercise on serum concentrations of iron and acute phase proteins in racing sled dogs

To determine effects of long-distance racing exercise on iron status in endurance racing sled dogs, with or without anemia. Prospective cohort study. 114 dogs that participated in the 2007 Iditarod Trail Sled Dog Race (59 and 55 dogs that did or did not complete the race, respectively). Stored serum samples obtained from 85 endurance-racing sled dogs that were expected to participate in the race were used to establish study reference intervals and prerace group values for iron-related variables. Blood samples collected from 114 study dogs before (ie, baseline) and after participation in the race were used to determine PCV and serum total protein concentrations before and after racing and assess iron-related variables after racing. Mean values for PCV and serum total protein concentration were decreased after racing, compared with baseline values in the same dogs. Mean serum iron concentration was low, and mean serum ceruloplasmin and C-reactive protein (CRP) concentrations were high in dogs after racing, compared with prerace group values. Mean serum ferritin concentration was high in dogs that did not complete the race, compared with the prerace group value and that of dogs that finished the race; 4 of 113 (3.5%) study dogs had low ferritin concentrations (< 73 ng/mL) after racing, suggestive of possible iron deficiency. Decreased PCV and serum total protein concentrations were consistently detected, whereas iron deficiency appeared to be uncommon, in study dogs after race participation. High serum concentrations of ceruloplasmin and CRP after racing suggested that changes indicative of iron deficiency may be masked by inflammation. Alternatively, changes in serum iron and CRP concentrations may reflect a physiologic response.

Determination Of Total Energy Expenditure Of Dog Sled Drivers During A 1049-mile Iditarod Race

The Iditarod dog sled race provides a unique opportunity to study the rate of human energy expenditure during extended exercise with the added challenges of sleep deprivation, extreme cold and the management of a large team of dogs. In addition, the distribution of macronutrients and the fitness of the driver are important in order to guide the team through steep and icy conditions during a multi-day race. PURPOSE The purpose of this study was threefold: (a) to assess the total energy expenditure (TEE) of the musher, (b) to determine the distribution of macronutrients ingested during the race and (c) to estimate the fitness level of the dogsled driver (musher) prior to the race. METHODS Five mushers from the Iditarod sled dog race were recruited as research subjects to receive doubly labeled water, with three agreeing to monitor food intake. Four out of the five subjects completed the entire race. Pre-race estimate of aerobic fitness (VO2peak) using a multi-stage bench stepping protocol were also determined. RESULTS Doubly labeled water data demonstrated an average TEE of 20.8 MJ·d−1 (4972 kcal·d−1) from Anchorage to Nome for our male subject, with an average of 11.8±1.7 MJ·d−1 (2808±397 kcal·d−1) for the female subjects during the race. Food records suggested an average distribution of macronutrients of 1.5±0.4, 3.9±0.4 and 1.7±0.9 g·kg−1 for protein, carbohydrates and fats, respectively. Estimated VO2peak was 66.2 ml·kg−1·min−1 and 50.0±8.4 ml·kg−1·min−1 for the male (n = 1) and female subjects (n = 4), respectively. CONCLUSION These data demonstrate that dogsled drivers, with an above average estimated VO2peak, maintain consistent, high daily total energy expenditure (TEE) throughout all phases of the race.

Exercise stress, intestinal permeability and gastric ulceration in racing Alaskan sled dogs

AbstractSustained strenuous exercise has been shown to produce gastrointestinal disease in athletic species, but the causative factors remain unknown. Since exercise results in oxidative stress and hypercortisolaemia, we tested the hypothesis that oxidative and physiological stress cause gastrointestinal disease in racing Alaskan sled dogs. Dogs from three racing teams were examined before (pre) and immediately after (post) completing a 1770-km sled dog race in approximately 11 days. Serum cortisol and isoprostane concentrations were compared with markers of gastrointestinal barrier integrity and endoscopic evidence of gastric ulceration. Gastric barrier integrity was assessed by measuring the urinary recovery of sucrose and intestinal barrier integrity was assessed using the urinary recovery ratio of lactulose to rhamnose (L/R), administered together by orogastric gavage. Exercise produced a significant increase in median serum cortisol (pre: 1040, 717–2946 pg ml−1(range); post: 8072, 2228–29 571 pg ml−1;P&lt;0.0001) and L/R recovery ratio (pre: 0.110, 0.060–0.270; post: 0.165, 0.080–0.240;P=0.009) but not isoprostane (pre: 1007, 656–2305 pg ml−1; post: 1164, 23–4710 pg ml−1;P=0.194) concentration. The increased serum cortisol concentration was not correlated with a change in L/R recovery ratio or urine sucrose concentration. Dogs with abnormal gastric endoscopy results (61% of finishers) had higher serum cortisol concentrations than dogs with normal endoscopy results (P=0.0007). We have demonstrated concurrent hypercortisolaemia and gastrointestinal barrier dysfunction with no correlation of the two. Thus, our data do not provide support for the hypothesis that increased serum cortisol concentration causes exercise-induced gastrointestinal disease.

Sustained Strenuous Exercise Increases Intestinal Permeability in Racing Alaskan Sled Dogs

We assessed gastric and intestinal permeability and performed gastroscopy to evaluate the effects of sustained strenuous exercise on the gastrointestinal tract in racing sled dogs. Three teams of racing Alaskan sled dogs were examined approximately 1 week before and 24 hours after the 2003 Iditarod sled dog race (1,100 miles in 10 days). Each examination consisted of the administration of a solution of sucrose, lactulose, and rhamnose to evaluate gastric and intestinal permeability, as well as gastroscopy to visually inspect the gastric mucosa. Of the 54 dogs examined before the race, 16 completed the course and contributed data to the analysis. Sustained strenuous exercise was associated with an increased frequency of gastric erosions or ulcerations seen endoscopically (0% prerace versus 61% postrace). A significant postrace increase occurred in the median lactulose to rhamnose ratio in both serum and urine (0.11 versus 0.165, P = .0363; 0.11 versus 0.165, P = .0090, respectively). No significant differences were found in median serum or urinary sucrose concentrations when pre- and postrace values were compared. No correlation was found between visible gastric lesions and the concentration of sucrose in serum or urine samples obtained 4-5 hours after administration of the sugar solutions. We conclude that sustained strenuous exercise is associated with increased intestinal permeability, but the sucrose permeability test as we performed it did not correlate with visible gastric lesions.

Muscle injury and antioxidant status in sled dogs competing in a long-distance sled dog race

AbstractExercise is associated with an increase in the production of oxidants that may be instrumental in the development of exertional rhabdomyolysis. We speculated that participation in a long-distance sled race would alter antioxidant capacity of dogs, in conjunction with increases in indices of rhabdomyolysis. The objective was to determine the effect of participation in a long-distance sled dog race on antioxidant capacity and plasma creatine kinase (CK) activity in sled dogs. This was a prospective, longitudinal study on a convenience sample of 57 Alaskan sled dogs participating in a 1600 km sled dog race. Blood samples were collected before racing (31 dogs) and after racing (39 dogs) for measurement of plasma vitamin E concentration; CK, aspartate aminotransferase (AST) and caeruloplasmin (CER) activity; and red-blood-cell (RBC) glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity. CER and GPX activities after the race were 26% and 14% lower, respectively, than before racing whereas CK and AST were 300% and 170% greater. There was no change in plasma vitamin E concentration or RBC SOD activity. We conclude that completion of a long-distance sled dog race involving prolonged and repeated submaximal exercise results in a reduction in enzymatic antioxidant activity in the blood of sled dogs.