Written by Dr. Vicky Lauer. 

Managing ventilation during the winter and early spring is challenging for many naturally ventilated barns. It’s common for the weather to change daily (if not hourly) in the Midwest, going from sunny and calm to snow and wind. Huge temperature swings turn ventilation into a chore as curtains need to be raised or lowered. That’s assuming the curtains aren’t frozen in place! While it may be tempting to leave the curtains barely cracked or even closed throughout the winter, maintaining proper ventilation is a requirement for healthy cattle.

First, let’s define ventilation: the process by which clean, outside air is intentionally provided to a space and stale air is removed. Cows generate a considerable amount of body heat due to their large mass and built-in fermentation vat (AKA the rumen). The heat they produce must escape the barn somehow, and since warm air rises it leaves through the central ridge in a naturally ventilated barn. “Nature Abhors a Vacuum,” so when warm air escapes, fresh air from outside must take its place. When the curtains are cracked at the top, fresh air enters the barn from above the curtains, falls along the outside wall, then mixes with air in the barn before warming and escaping through the peak. This is the foundation of a naturally ventilated barn. Without both an inlet for fresh air (no matter how cold that air is) and an outlet for old air, effective ventilation is impossible.

When a barn lacks an inlet due to the curtains being closed, the barn gets not only warm but also humid. Each cow exhales over 4 gallons of water per day while breathing, which we see visually as “fog” in the barn. Higher temperature and humidity allow bacteria to grow, thus increasing the chance of pneumonia. Unfortunately, every year I hear of a dairy with a winter pneumonia outbreak. The root cause is often closed curtains that were never re-opened after adverse weather had passed. The barn got hot and steamy, and cows got sick. One of the first things I recommend is opening the curtains. While vaccines can minimize pneumonia, efficacy is limited if ventilation is poor or absent. Yes, opening and closing curtains based on weather can be a miserable job, but it is vital for cow health. Keep those curtains cracked!

What about calves? Hutches provide the ultimate clean air but are a winter management nightmare which is why calf barns are popular. However, pre-weaned calves don’t generate enough body heat to naturally ventilate a barn. Thus, calf barns require mechanical means to remove stale air and provide fresh, clean air. There are various mechanical systems for calf barns, but properly designed positive pressure ventilation (PPV) systems are proven to provide closest-to-optimum air quality. The Dairyland Initiative website includes a list of trained professionals who can help design a PPV system. Again, vaccines can’t prevent pneumonia if ventilation is a problem.

Let’s keep those cows and calves healthy by optimizing ventilation in 2025!