• horse;
  • particulate matter;
  • airway inflammation;
  • coarse particles;
  • fine particles;
  • ambient monitoring;
  • Thoroughbred racehorses


Reasons for performing study: Airway inflammation and mucus in the trachea are common in racehorses. Fine airborne particles can initiate and coarse particles can worsen airway inflammation in man and in animal models of airway disease. The regional and seasonal distribution of particles of different sizes has never been investigated in American racing stables.

Objectives: To determine the regional and seasonal concentration and number of airborne particles of different sizes in racing stables.

Methods: Direct reading instruments were used to determine the mass concentration and numbers of particles 3 times daily (early morning, midday and late afternoon) in July, September and November, in 3 different racing stables.

Results: Average particle concentrations were lowest in July and highest in September and November. Early morning concentrations were significantly higher than those measured throughout the rest of the day. The completely enclosed stable with little natural ventilation, had significantly higher particulate concentrations than the open-sided stable. With regard to numbers of particles, those 2–5 µm were greatest in July and least in November; those 0.5–1.0 µm were greatest in September and least in November. Location of stall within stable also affected concentrations and numbers.

Conclusions: The concentration and number of particles in sizes known to reach the lower airways varies with stable design/management, time of day, season of year and location of the stall within the stable.

Potential relevance: Particle mapping is a useful tool in the identification of stables, season, and location of stalls within stables where horses may be at greater risk of exposure to offending particulates.