When the Dust Settles: Barn Air Quality Can Negatively Impact Equine Respiratory System

By Cynthia McFarland

Horse Stable

How many times have you noticed dust motes dancing in a shaft of sunlight spilling through your barn window? To a photographer, it’s a tranquil moment waiting to be captured. But those dancing particles can be a constant source of airway irritation to the horses in that barn.

Inadequate ventilation, dusty bedding, stall cleaning, hay fed in hay nets or raised feeders (instead of at ground level), closed or small windows, closed stall fronts, overhead hay lofts, sweeping and blowing of aisle ways, and indoor riding areas can all contribute to poor air quality in the barn.

When horses are exposed to this kind of stable environment, they can develop respiratory disease. Inflammatory airway disease is among the most common problem and can over time progress to heaves (chronic obstructive pulmonary disease) in some horses. Poor air quality can also lead to increased mucous in the airway; coughing upon initiation of exercise, even if coughing subsides shortly; decreased stamina (which leads to decrease in performance); delayed respiratory recovery time after exercise; and exercise intolerance.

“A big misconception is people thinking that a horse coughing is normal. A horse coughing whenever it goes into a stall or an arena may be common, but it isn’t normal. Coughing when a horse starts to exercise is usually a sigh of underlying respiratory disease,” said Melissa Mazan, DVM, Diplomate ACVIM, associate professor in the Department of Clinical Science at Cummings School of Veterinary Medicine Tufts University in North Grafton, Massachusetts.

Lower respiratory illness is well documented in horses, and according to Mazan, the amount of dust in barns is typically considered the reason.

“If you talk to people active in human pulmonary work, they are stunned that particulate matter can be so high in stabled horses,” says Mazan, who has also conducted human pulmonary stem cell research.

Tufts University has conducted several studies over the years relating to air quality in horse barns. One method used was the DustTrak monitor, a laser counter that samples the air at a steady rate and reveals how many particulates are present. Another method collects the dust particles with a pump that draws air through a “cyclone,” a device that measures exposure to dust. This allows researchers to actually look at the dust to determine the presence of endotoxins, which are the toxic substances found in certain disease-producing bacteria and liberated by the disintegration of the bacterial cell.

One study followed a group of horses stabled inside an enclosed barn, while another group was kept in an outdoor dirt paddock. The study looked at ten horses, which were sampled in 24-hour periods. Each horse had a “cyclone” attached to its halter, while a small pump attached close to its nose drew in air in much the same location as the horse does when breathing.

Even though the outdoor horses were in a dirt environment without grass and were fed the same hay as the stabled horses, the study revealed that particulates were actually very low in this setting. It was another story, however, for horses stalled inside the barn.

The particulate count in the barn increased dramatically when people were sweeping or using blowers in the barn aisle, throwing bales of hay down from the loft and shaking hay out at feeding time. Cleaning stalls also raised the particulate level when workers tossed and/or sifted the bedding to separate out manure and soiled areas.

“Barns are very high in endotoxins, which are found in hay, manure and grain,” says Mazan. “There are gram positive and gram negative bacteria, but it doesn’t matter whether the bacteria are alive or dead; it can still cause inflammation.”

Mazan adds that research has indicated when outdoor horses develop respiratory problems, it is often more connected to mold spores than to dust. This can be particularly problematic in the South when there is high “mold bloom.” This can depend on the type of plants in the area and whether or not the pasture has been de-thatched. Fields with heavy thatch can serve as a prime place for mold spores to develop and “bloom.” (Equipment can be rented or purchased to de-thatch lawns and pastures.)

Pollen can also pose a problem and not just because a horse has allergies to a certain plant.

“You can have problems when there is a lot of pollen and horses don’t have to necessarily be allergic to it,” Mazan explains. “Pollen as a particulate can cause respiratory inflammation and it carries endotoxins, which can cause a lot of respiratory inflammation.”

When horses are exercised indoors, testing has shown extremely high particulate levels if the surface is not dampened.

Bedding is often a source of significant dust. Avoid sawdust, which has a heavy amount of fine particulate matter compared to shavings. If you use shavings or straw, purchase the cleanest you can find.

Stall and barn flooring can also be a source of dust. For example, clay floors can have a significant amount of dust because the clay is ground up due to the horse’s weight. You can use rubber mats atop clay, but an even better option is to use mats over crushed rock or popcorn asphalt. Better still, although more costly, is a seamless rubber flooring system.

Storing hay or straw in an overhead loft is not only a fire hazard, but is a major contributing factor of dust and also inhibits good ventilation.

It doesn’t take serious environmental testing to determine if barn air quality can be improved. An observant walk through the barn during times of highest activity and again during quiet periods can be surprisingly revealing.

“Look around and ask yourself, ‘What am I doing that is causing dust?’” advises Mazan. “For example, wet down the aisle way before you sweep or use a blower. If you are having problems, have an expert come in and look at airflow patterns and suggest modifications. It might be a question of adding vents, fans, and changing configurations.”

Simple management practices can make a noticeable improvement:

  • Always take horses out of the stall before cleaning them. You may even want to lightly dampen bedding before bringing horses back in
  • Use the cleanest possible sources of bedding
  • Use rubber mats in stalls under bedding
  • Don’t blow or sweep in the barn when horses are present
  • Feed hay at ground level instead of from wall racks or hay nets to keep horses from inhaling dust and hay particles
  • Promote good ventilation practices in barn and avoid a warm, closed-up barn at all costs

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