Dairy barn ventilation remains important in winter months

Air quality in dairy barns involves much more than carbon dioxide, methane, ammonia and hydrogen sulfide. 

Other compounds can be present in the headspace, including a wide range of volatile organic compounds (VOCs) originating from feed, manure, bedding, animals, equipment and vehicles. These compounds differ significantly in their chemical properties and effects on the health of animals and humans alike.

Chemicals and air quality

The impact of a chemical on air quality is not always proportional to its concentration. In some cases, chemicals found at very low concentrations can be more harmful than those found at higher levels. 

The chemical structure and reactivity of each compound determine its potential impact.

For example, p-cresol, which is a product of microbial degradation of tyrosine – an amino acid – is typically detected at parts-per-billion levels. However, it is a major contributor to odor emissions and has been linked to significant health conditions in humans. 

In addition to VOCs, particulate matter from dried manure, bedding, hair, feed and vehicles is another important factor influencing air quality in dairy facilities. Particulate matter is known to have health impacts. They may also include bioaerosols, which are airborne particles containing biological material. 

The amount of these airborne compounds depends strongly on ventilation design and air exchange rates. As temperatures drop, farmers typically transition from summer ventilation rates of up to 60 air exchanges per hour to winter rates as low as four air exchanges per hour. 

Although emissions decrease at lower temperatures, maintaining enough air exchange is essential to prevent areas with little to no circulation. 

When ceiling fans are used, they should be switched from counterclockwise – downward airflow – to clockwise – upward airflow – to promote gentle air mixing without creating drafts.

If air circulation is poor, compounds heavier than air – most compounds other than ammonia and methane – can accumulate near bedding surfaces. Over time, these stagnant pockets contribute to declining air quality.

High-risk areas

Preliminary studies conducted at the Blaine Dairy Cattle Center at the University of Wisconsin-Madison indicate two areas with higher risk. 

The first high-risk area is calving pens with straw bedding. As expected, compared to sand bedding, straw tends to produce higher emissions due to its organic composition, microbial activity and moisture content. 

Keeping straw bedding clean and dry in calving pens helps reduce air emissions, with most farms adding fresh bedding several times per week.

Producers should do a complete bedding change and thorough cleaning between calvings or once per month, depending on bedding moisture. 

The second high-risk area is the central alley. 

Fresh air enters through the sidewall curtains, but the central alley frequently remains one of the lowest airflow zones in dairy barns.

Although airflow is limited in this area, it is also where workers spend most of their time. 

When conditions allow, opening end-wall doors can help improve air movement, particularly when ridge vents are covered to prevent precipitation from reaching the bedding and natural ventilation becomes restricted.

Nesli Akdeniz is a University of Wisconsin-Madison Extension controlled environments specialist. This article was originally published by Wisconsin Agriculturist on Nov. 21, 2025.