Page 75 - December 2020

VETERINARY VIEWS
THE BREATHING ZONE
Equine health is optimized by eating high fiber forage, such as hay and/or pasture. Studies show that while a horse eats dry hay, dust
may be 30 to 40 times higher in the breathing zone – the air around a horse’s nose – than in the rest of the stall, whereas if fed low-dust products, like pellets, quality hay cubes or haylage, dust levels are equivocal throughout the stall. Other studies demonstrate that
horses eating hay (round or square bales) have increased airway inflammation compared to horses grazing pasture. Ironically, although
a high forage diet such as hay contributes to gastrointestinal health, hay is a source of dust and airway contamination for horses.
The stall environment has a huge impact on health of the respiratory tract. Particulate levels are very high especially during the feeding period and during stall cleaning – as high as 12 - 15 mg/cubic meter measured within the horse’s breathing zone. This is much higher than OSHA-recommended (Occupational Safety and Health Administration) dust exposures for humans. Indoor arenas pose an additional potential risk by aerosolizing dust and debris to high levels of 60 mg/cubic meter as horses move around the arena, particularly with dry footing. Not only are the horses exposed to high levels of inspirable dust, but so too are riders, grooms, and workers.
WHAT IS IN THOSE DUST MOTES?
One source of environmental pollutants with a marked effect on the airways is endotoxin, which is a component of the
cell walls of Gram-negative bacteria. A
horse with a severe infection, as for instance pleuropneumonia, has symptoms of fever
and high heart rate – these are due to endotoxin. Ordinary components of barn life, such as grain, hay, bedding, horse dander, and manure are chock full of endotoxin. Studies
in humans and laboratory animals show that inhaled endotoxin causes airway inflammation; humans exposed to high levels of inhaled endotoxin, such as people working in poultry barns or cotton factories, have greater declines in lung function over time.
Other environmental contaminants – ammonia and mold – additionally irritate
the airways. Moldy hay is more offending to the airways than clean, ‘bright’ hay; baked, chopped hay, and fermented products like haylage are even lower in dust. Buy these products only from a commercial vendor and carefully read labels as fermented hay products can harbor botulism toxin if not prepared properly. Paper or pelleted bedding is preferable for its lower dust content than straw, shavings, or sawdust, which are quite dusty.
“Summer pasture-associated recurrent airway obstruction” occurs more often during times of the year when mold spores are found in high concentrations in the air, as occurs in the South. Even in New England many horses have exacerbations of equine asthma during hot humid weather, not just during the winter when confined to stalls.
DETRACTING FROM PERFORMANCE
Airway inflammation can impact performance, particularly of a horse engaged in high-speed sports, like racing. An array of clinical signs includes poor racing performance, coughing, and mucus accumulation in the airways due to inflammation. These horses may fade through
a race, have reduced stamina during training,
and have protracted recovery following hard works, evidenced by an increased and prolonged respiratory rate and effort. Affected horses don’t have a fever yet have a normal appetite and no clinical evidence of systemic disease at rest. The stress and increased effort of intense exercise such as racing, or training amplifies clinical signs.
Even small amounts of tracheal mucus related to inflammation are associated
with horses finishing further back in a
race. Horseracing performance is limited by lung function rather than cardiac output –
any decrease in lung capacity likely decreases performance, especially in a horse that is exercising at maximum intensity. In one study, horses with no or scant amounts of tracheal mucus were nearly twice as likely to finish well in a race compared to horses with moderate to severe amounts of mucus in their trachea.
Equine asthma is recognized sooner
in racehorses because of the need to use
every ounce of their respiratory reserve to perform. Despite no history of cough or nasal discharge, a racehorse may evidence only a single respiratory sign of slower recovery of respiratory rate. In contrast, “sport horses” may not signal respiratory impairment until the horse is coughing continuously at exercise or has a chronic nasal discharge.
Training and racing on a track add to airway compromise. Consider the post-race appearance of horses by looking at their heads, necks, and chests smeared with dirt and debris. Similarly, jockey goggles and faces are splattered with dirt, dust or mud from the materials kicked up from the track. Such debris and particulate matter impact the airways, and hence performance. The farther away from the lead position, the more particulates a horse is exposed to; this is exacerbated by dry, dusty surfaces.
In addition, exercise-induced pulmonary hemorrhage (EIPH) is associated with lower airway inflammation, so any measures taken to minimize respiratory irritation also help to reduce the occurrence of bleeders.
Heaves and inflammatory airway disease are two common lower respiratory syndromes that are now both lumped under one heading of Equine Asthma.
Studies show that while a horse eats dry hay, dust may be 30 to 40 times higher in the breathing zone – the air around a horse’s nose – than in the rest of the stall, whereas if fed low-dust products, like pellets, quality hay cubes or haylage, dust levels are equivocal throughout the stall.
Ordinary components of barn life, such as grain, hay, bedding, horse dander, and manure are chock full of endotoxin, which causes airway inflammation.
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