Very interesting artilce for those who work their horses in very cold
temps.
From "The Horse"
Cold Air and Lung Health by: Melissa Sykes April 2005
Researchers at Oklahoma State University (OSU) recently completed a
study on airway cooling and mucosal injury during cold weather exercise. Using
the Thoroughbred racehorse as a model, scientists found that even cantering in
sub-freezing temperatures can induce airway obstruction (bronchoconstriction, or
airway contraction). The research appeared in the February issue of the Journal
of Applied Physiology.
Human subjects that routinely perform strenuous exercise in cold
conditions have a higher prevalence of chronic airway inflammation and
hyperactivity (often referred to as "ski asthma" because its effects are often
found in cross-country skiers). The scientists set out to determine whether
exercise while breathing cold air could cause chronic airway disease in the
equine athlete.
Previous studies in both humans and horses have confirmed that when
exercising in subfreezing temperatures with low humidity, the upper airways fail
to fully warm the inhaled air, leading to considerable loss of heat and water
from the lower airways. These studies also confirmed that this stimulus is
associated with airway mucosal damage.
"Our data show that exercising in cold air can provoke airway changes
in otherwise healthy horses and may in fact be a part of the cause of the
eventual development of chronic airway disease in equine athletes," explained
lead researcher Michael S. Davis, DVM, MS, PhD, Dipl. ACVIM.
The effects were seen in horses exposed to exercise/cold air
during a single challenge (five minutes of easy cantering).
"We intentionally ran the horses at a slow canter to avoid airway
bleeding and, as a result, had to reduce the temperature of the inhaled air to
compensate," said Davis. "We published an earlier study (in a supplement to the
Equine Veterinary Journal in 2002) in which we demonstrated that a similar
challenge will be delivered at a fast canter or gallop with air temperatures
above freezing. Thus, this is not just an issue for horses running way up north
or in the dead of winter. Part of our previous study was done on horses training
at Pimlico (Baltimore, Md.) in late March and early April."
Once the challenge was over, the airways returned to normal, but, "We
don't know how long it took as we allowed them a minimum of two weeks before we
tried anything else," Davis added. "The reality is that horses that
experience one challenge are likely to experience repeated challenges three to
four times a week while training. The time it takes these cumulative challenges
to resolve is probably quite a bit longer.
"We've done similar studies in sled dogs and found that it takes more
than four months to resolve," he said. "We are considering studies in both
horses and sled dogs to see if they perform better if and when we make the
airway inflammation go away."
Researchers feel the effects of cold weather exercise might inhibit the
immune response.
But, Davis stressed, these studies do not demonstrate conclusively that
the horse's immune system is suppressed, "Only that they might have trouble
responding to certain types of infection."
"We're currently developing those studies (on the immune response),"
added Davis. "Obviously, the results would potentially apply to humans since
the cold and flu season seems to be in the winter."
