When to open the barn doors

An expert weighs in on one barn community's disagreement on when to leave the aisle doors open.

 Q: Please settle an argument at our barn. Should the large doors at the end of the aisle be left open all night? Doing so makes the barn about 15 degrees colder, but the air is “fresher” and the entire barn smells better in the morning. Are the horses at the end of the aisle at greater risk for illness if the doors are left open because of any drafts they might experience?

A: I hate to take sides in a barn dispute, and there is some truth on both sides of this one! A lot depends on the amount of ventilation in this barn, and on the ambient temperatures inside and outside.  

A person walking down a barn aisle with a horse, seen in the shadow.
Generally speaking, more barn ventilation will limit asthma and other types of reactive airway disease

Regarding air quality, it is important to know that even when a barn is meticulously maintained, ammonia commonly accumulates when the doors and windows are closed, and can contribute to respiratory irritation and asthma, or even mild infections. And hay and barn dust inside a barn can also contribute to asthma, so opening the doors overnight can be a good tactic for decreasing those allergens.  

Now, this logic might be flipped on its head in circumstances when the outside air is cruddy. I might opt to close the doors to limit dust from construction and agriculture, and here where I am in the Northern Rockies, wildfire smoke was a fact of life all summer, which means that pro-viding filtered air via a ventilation system is often preferable—at least for certain days or weeks.

Generally speaking, more barn ventilation will limit asthma and other types of reactive airway disease and, in turn, that will limit the kinds of mild secondary infections that can accompany asthma. 

In terms of ambient temperatures, it might help to know that a 15 or 20 degree temperature differential between the heat of the day and the cool of the night are not considered a huge risk factor for any type of illness for healthy adult horses. In fact, temperature swings of 30 to 50 degrees are typical here in the Northern Rockies on any given day, and horses do just fine.  

That said, there is some association between colic symptoms and changes in weather.  In part, that is because horses may not drink enough water in cold weather. 

So, when peak temps change by more than 20 degrees in either direction, it is wise to take extra precautions.  In other words, when tomorrow’s peak and/or lowest temperatures are projected to be at least 20 degrees colder than today’s,
I advise some caution. 

Monitor water intake, consider adding blankets, and yes, this would be a reasonable time to consider keeping the barn closed up tight.  After a week or two of consistent weather, even if it is quite cold, horses will usually have acclimated
and less concern is warranted. By the same token, if tomorrow’s peak temperature is projected to be at least 20 degrees warmer, horses are likely to require additional water intake, and strategies like fans, misters and open barn doors can really help during a period of acclimation. 

It is probably obvious, but you can also use your powers of observation to see if horses look cold.  If they look anxious, or “humped up,” or it seems like their hair might be standing on end, that would be a good indication to add a blanket, or to let that particular horse be in a stall that isn’t near the big doors that are being left open overnight.

In a nutshell, like so many aspects of horse husbandry, the answer is, “It depends”! You’re both right, but as you can tell, I tend to recommend more airflow rather than less, assuming ambient conditions and all other aspects can remain stable in the stable.   

Peter Heidmann DVM, MPH
Three Forks, Montana

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