Horses today don’t always have ideal conditions for clean air. We often keep them confined indoors with poor ventilation, feed hay that contains some dust and molds, or ride them in a dusty arena. Dr. Melissa Mazan, Associate Professor and Director of Equine Sports Medicine at Tufts Cummings School of Veterinary Medicine says it’s always a balance to try to determine whether keeping a certain horse indoors or outdoors is better. The outside environment is often better than the dusty air in an enclosed barn, but on days with air pollution, or high pollen levels, the horse may be better off indoors.

This may depend on where you live and what the weather is like. If you live in the South, or even some other regions of the country, your horses may experience breathing difficulties outdoors during wet, warm seasons. “This is sometimes due to breathing mold spores, but in this instance it’s out in the pasture instead of in the barn. The summer pasture associated reactive airway diseases are due to the same problem – overwhelming exposure to things the lungs don’t like,” says Mazan.

“Though we usually think of this being a southern problem, we also see it in the Northeast and other regions, when mold blooms are high. There are things you can do to help prevent this and one is pasture care. Many people don’t think about getting their pastures de-thatched, but this can help. Think of it like grooming a dog; when there is a thick under-layer of hair you must brush the hair coat to get it out. Pastures sometimes get like that also, with a deep under-layer of grass. If you have a lawn and want good green grass in the summer, you need to rake it in the spring to get all the dead grass out. That dead thatch is a beautiful place for mold to flourish,” she explains. “Molds tend to all bloom at once when conditions are right, so you have this sudden expelling of huge numbers of spores into the air. This can cause breathing problems.”

Pollen season can also bring on respiratory distress. “Some people are looking for allergens to blame for breathing problems, but it doesn’t take a specific allergy. Pollen, for you or your horse, contains a high level of endotoxin. Hay dust, shavings and arena dust are high in endotoxins, and so is grain. Endotoxins are produced in the outer walls or pieces of the outer walls of dead gram-negative bacteria. These endotoxins can cause airway inflammation.” If you or your horse breathes in a lot of pollen, an adverse reaction doesn’t necessarily mean that you are allergic to the pollen. Allergy may be one component, but not the only factor. The main problem may be a toxic inflammatory reaction.

If your horse is pastured next to a crop of corn or alfalfa, there may be times in the spring or summer that the pollens are detrimental, if the prevailing breezes bring these over the pasture. Getting the horse indoors may help, though some of the pollen may also come inside the barn via air ventilation/circulation.

In summer when it’s dry, and weather is clear, your horse may still have problems if where you are riding gets dusty. “Sometimes there may also be a lot of ozone in the air, which may be a factor in air quality. We don’t have much data about ozone, but studies that were done a while ago in England showed that greater exposure to ozone results in worse lung function in horses. In general, ozone is not good for humans, particularly sick ones. If you have a horse that you know has respiratory problems, and you know the air quality is poor outside, it might be wise to bring that horse indoors that day if you have a barn that’s well ventilated,” she says. But being in a dusty barn won’t be better than being outside.

If air quality levels will be poor on a particular day, forecast in weather reports or on the internet for your region, keep in mind that it’s not just going to be bad breathing conditions for you, but also for your horse, especially if you are riding him. “Your horse is probably breathing harder and deeper than you are; he is working harder than the rider, and getting more of that bad air in the lower airways,” explains Mazan.

To look at the big picture, think in terms of reducing exposure to dust and endotoxins, which often go hand in hand. “Keep the horse’s environment clean. Prevent dusty situations. Some of that will be out of your control, but other factors are not. If you can reduce any of the respiratory irritants, this can help, since it is usually cumulative respiratory stresses that add up to create a problem.

The horse may be able to tolerate some mold spores or some dusty shavings, but when he is ridden in a dusty arena he coughs. Work on the particular conditions you can control, to improve them, such as sprinkling the hay or the arena, or finding a less dusty feed.

Regardless of where you live, the important thing is to reduce the amount of dust, exposure to molds, pollens, etc. and to think about ways you can achieve cleaner air for the horse.