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CARRIAGE HORSES
Expert Opinion
AIRWAY COOLING AND MUCOSAL INJURY DURING COLD WEATHER EXERCISE
Davis MS, Lockard AJ, Marlin DK, Freed AN
Equine Vet Journal 2002 Sep ;(34):413-6.
Equine Athletic Performance Laboratory, Oklahoma State University College
of Veterinary Medicine, Stillwater 74078, USA.
In human subjects that exercise strenuously in cold weather, there is
evidence that hyperventilation with cold air leads to peripheral airway cooling,
desiccation and mucosal injury. Our hypothesis was that hyperventilation with
cold air can result in penetration of unconditioned air (air that is not
completely warmed and humidified) into the peripheral airways of exercising
horses, resulting in peripheral airway mucosal injury. To test this hypothesis,
a thermister-tipped catheter was inserted through the midcervical trachea and
advanced into a sublobar bronchus in three horses that cantered on a treadmill
at 6.6 m/s while breathing cold (5 degrees C) [= 41 degrees F] air. The
mean (+/- s.e.) intra-airway temperature during cantering was 33.3 +/- 0.4
degrees C, a value comparable to the bronchial lumen temperatures measured in
man during maximal exercise while breathing subfreezing dry air. In a second
experiment, 6 fit Thoroughbred racehorses with satisfactory performance were
used to determine whether strenuous exercise in cold conditions can produce
airway injury. Horses were assigned to Exercise (E) or Control (C) groups in a
random crossover design. Samples of bronchoalveolar lavage fluid (BALF) in the E
treatment were recovered within 30 min of galloping exercise in 4 degrees C,
[=39 degrees F] 100% relative humidity (E), while in C BALF samples were
obtained when the horses had not performed any exercise for at least 48 h prior.
Ciliated epithelial cells in BALF were higher in E than in the C treatment.
Similar results have been found in human athletes and laboratory animal models
of cold weather exercise. These results support the hypothesis that, similar to
man, horses that exercise in cold weather experience peripheral airway mucosal
injury due to the penetration of unconditioned air. Furthermore, these results
suggest that airway cooling and desiccation may be a factor in airway
inflammation commonly found in equine athletes.
[NOTE: ACCORDING TO NYC LAW, HORSES ARE ALLOWED TO WORK AS COLD AS 18 DEGREES
F.]
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