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Detection of Respiratory Disease in Horses
Laurent Couetil, DVM
Respiratory disease is the second most common cause of decreased
performance and premature retirement among racehorses.
Exercise-induced pulmonary hemorrhage (EIPH), or lung bleeding,
and inflammatory airway disease (IAD) are by far the most common
respiratory problems. A diagnosis of EIPH is often made shortly
after strenuous exercise by visualizing blood in the trachea
using an endoscope. Only a small percentage (less than 10%) bleed
through their nose (epistaxis). A diagnosis of IAD is often made
by visualizing excess secretions or mucus in the trachea post
exercise. Affected horses may also cough intermittently.
Several studies have shown that up to 95% and 65% of racehorses show
signs of EIPH and IAD respectively. Obviously, not all of these
racehorses are poor performers. Therefore, the problem is
determining whether or not the EIPH or IAD is severe enough to
impair the respiratory function, i.e. blood oxygenation during
exercise.
We recently conducted a study looking at sensitive ways to detect
impairment of lung function in racehorses with EIPH or IAD. The
study included 36 horses (20 Standardbreds and 16 Thoroughbreds)
from various parts of Indiana. Each horse was evaluated over a
3-day period. The results of the study show that horses with EIPH
or IAD have lower blood oxygen levels than normal horses during
treadmill testing. In addition, horses performing poorly exhibit
lower blood oxygen levels than good performers. Nevertheless,
some good performers have IAD or EIPH.
Another test used was a benign procedure consisting of sampling
the deep lung using a long endoscope (bronchoalveolar lavage or
"lung wash"). Results indicate that horses with EIPH or IAD have
specific features that are very helpful in making the diagnosis
and recommending treatment. These special tests allow us to
differentiate between allergic, inflammatory, and infectious lung
diseases. These lung diseases often go undetected for some time
because the only manifestation is decreased level of performance.
We conclude that measurement of blood oxygen level during
treadmill testing and bronchoalveolar lavage are sensitive
indicators of mild lung disease. In addition, these tests allow
us to quantify the degree of lung function impairment. This is
important not just for diagnostic purposes, but also to assess
treatment response
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