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Objective—To assess changes in muscle glycogen (MG) and triglyceride (MT) concentrations in aerobically conditioned sled dogs during prolonged exercise.

Animals—54 Alaskan sled dogs fed a high-fat diet.

Procedures—48 dogs ran 140-km distances on 4 consecutive days (cumulative distance, up to 560 km); 6 dogs remained as nonexercising control animals. Muscle biopsies were performed immediately after running 140, 420, or 560 km (6 dogs each) and subsequently after feeding and 7 hours of rest. Single muscle biopsies were performed during recovery at 28 hours in 7 dogs that completed 560 km and at 50 and 98 hours in 7 and 6 dogs that completed 510 km, respectively. Tissue samples were analyzed for MG and MT concentrations.

Results—In control dogs, mean ± SD MG and MT concentrations were 375 ± 37 mmol/kg of dry weight (kgDW) and 25.9 ± 10.3 mmol/kgDW, respectively. Compared with control values, MG concentration was lower after dogs completed 140 and 420 km (137 ± 36 mmol/kgDW and 203 ± 30 mmol/kgDW, respectively); MT concentration was lower after dogs completed 140, 420, and 560 km (7.4 ± 5.4 mmol/kgDW; 9.6 ± 6.9 mmol/kgDW, and 6.3 ± 4.9 mmol/kgDW, respectively). Depletion rates during the first run exceeded rates during the final run. Replenishment rates during recovery periods were not different, regardless of distance; only MG concentration at 50 hours was significantly greater than the control value.

Conclusions and Clinical Relevance—Concentration of MG progressively increased in sled dogs undergoing prolonged exercise as a result of attenuated depletion.

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in American Journal of Veterinary Research


Objective—To determine the effects of training and sustained submaximal exercise on hematologic values in racing sled dogs.

Design—Cohort study.

Animals—39 Alaskan sled dogs bred for endurance racing.

Procedures—Blood samples were collected prior to initiation of a 7-month training regimen (n = 39), after completion of the training regimen (19), and after completion of an 1,100-mile race (9), and a CBC, differential cell count, and flow cytometry for leukocyte surface antigens were performed.

Results—Both training and exercise caused significant decreases in PCV and hemoglobin concentration and significant increases in total WBC count. In contrast, training and exercise were not found to have significant effects on absolute numbers or fractions of CD4+ or CD8+ lymphocytes, other than a significant increase in the fraction of CD8+ lymphocytes associated with training.

Conclusions and Clinical Relevance—Results suggested that training and exercise induced changes in several hematologic values in racing sled dogs. Extracellular fluid volume expansion was the likely explanation for the training-induced decrease in PCV, and acute blood loss secondary to gastrointestinal tract bleeding was likely responsible for the decrease in PCV associated with acute exercise.

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in Journal of the American Veterinary Medical Association


Objective—To determine effects of exercise performed while breathing cold air on expression of cytokines and influx of neutrophils in airways of horses.

Animals—9 adult horses.

Procedures—In a crossover study, bronchoalveolar lavage fluid (BALF) was obtained 24 and 48 hours after each of 2 submaximal exercise sessions performed by horses while breathing warm (25°C) or cold (−5°C) air. Total and differential nucleated cell counts were determined for each BALF sample. Relative mRNA expression of cytokines in BALF cells was quantified by use of a reverse transcription–PCR assay.

Results—Horses had a modest but significant influx of neutrophils into the airways 24 hours after a single exercise session while breathing cold air. No other cell types were increased at 24 or 48 hours after exercising while breathing cold air. Continued increases in expression of cytokines interleukin (IL)-5 and-10 as well as proinflammatory cytokines IL-1, -6, and -8 were detected 24 hours after exercising while breathing cold air. Forty-eight hours after exercising while breathing cold air, expression of IL-10 was still higher than that for IL-10 after horses exercised while breathing warm air. Expression of tumor necrosis factor-α was significantly increased at 48 hours after exercising while breathing cold air.

Conclusions and Clinical Relevance—Exposure of intrapulmonary airways to cold air alters immunologic responses of horses for at least 48 hours. The increased expression of cytokines that suppress cell-mediated immunity may predispose athletes to viral infections of the respiratory tract following exercise in cold weather.

Full access
in American Journal of Veterinary Research