Feel the breeze: Ventilating the summer barn

By Kevin Jacque, DVM, PAS, Ohio State University

Summer is here, and so is that classic Midwest heat and humidity. This month, we will discuss ventilation and how to keep barns well-ventilated. This was requested by a reader, and I happily agreed. Ventilation is an important component of our animals’ summer (and year-round) health.

Firstly, we should distinguish between ventilation and cooling. Ventilation is the exchange of air within a space to bring in new, fresh air – usually from outside of a building. Cooling is the reduction of air temperature or body temperature through various means, such as wind speed, humidity reduction, and conditioning. We cannot always address ventilation by the same means as cooling and vice versa. Ventilation is still important in the winter (sometimes more important due to the nature of our animal housing) and is imperative to animal and human health. We must remove old air. “Old air” will be stale in nature – it contains pollutants like bacteria, dust, allergens, ammonia, carbon dioxide, carbon monoxide, VOCs, POCs, and small air particulates. Think about how you would not want to stand in a barn with a running diesel tractor for more than a few minutes unless the barn door was open.

Why do we ventilate barns? We established above that old, stale air contains more pollutants. These pollutants can reduce upper and lower airway physiological function. Ammonia is well-known to impair the ciliary elevator of the trachea. Normally, the cells in your trachea (windpipe) move little finger-like appendages to push “junk” up and out of the airway and away from the lungs. When ammonia reaches high enough levels, the ciliary elevator works much more slowly than normal or is impaired completely, inhibiting the junk removal process. Ammonia levels recommended in animal housing vary based on species and age. In general, the younger the animal, the lower the tolerance for ammonia. For calves, nursery pigs, and other young animals, the level of ammonia should be less than 5-10 ppm (parts per million). Human detection of ammonia varies among people, and the noticeable range can be anywhere from 5 to 50 ppm ammonia. Older animals can tolerate up to 25 ppm, but that does not mean that they will not be negatively affected.

We have discussed some reasons to ventilate, but let us review some ways to ventilate barns. There are two main types — natural and mechanical, but we can also add any variety of mechanical ventilation to a naturally ventilated barn, thusly hybridized. Natural ventilation uses normal air breezes and the flow of air by temperature. Naturally ventilated barns often have high sides (14-16 feet is ideal) and have some sort of ridge vent (either fully open or via chimneys). Mechanical ventilation is often encountered in newer barns or in barns designed for large-scale poultry and swine production. These barns may use curtains, fans, weeping walls (for temperature reduction), and manure-storage ventilation to adjust temperature and air exchange throughout the building. Mechanical ventilation can be done via analog or digitally controlled systems with data loggers and sensors. Other mechanical ventilation includes positive and negative pressure tube systems. Research from the last 10-15 years has proven that positive pressure tube ventilation (PPTV) systems can be utilized well for barns with poor natural ventilation or those that have high pollutant loads, such as calf nurseries, hog nurseries, and the old stable or bank barn where everyone mingles their 4-H or FFA projects. Some newer, larger facilities have large versions of PPTV systems, such as at the new exhibition barns at World Dairy Expo in Madison, Wis., and newer livestock buildings in Indiana and Kentucky.

What if I desire to better ventilate my barn? What are some things to consider? The nature of existing barn design may dictate what style of ventilation is needed. You may have to consider the hybridization of ventilating existing barns to provide adequate air exchange. Minimum air exchanges per hour would be at least 4 exchanges per hour (EPH), but that may not be enough. We see that EPH is closer to 10-15, which may be the minimum, especially when we consider humidity, pollutant level, and temperature. In the summer months, we increase the minimum to 40-60 EPH due to increased humidity and temperature. Humid air retains more particulates than dry air, and higher bacterial loads are more common. We should consider adding PPTV, fans, curtains, and opening all of the doors of old barns during the summer. Consult with your veterinarian and Extension personnel to create a plan for better ventilating your barn. There are tools that can measure the air speed, bacterial load, and particulate matter levels in your barn. Older animals can usually tolerate higher air speeds if needed, but young animals can be sensitive to drafts, especially in the winter.

In general, ventilating barns may require more fans or curtains, and opening the barn as much as possible during the summer months. We can also consider tunnel ventilating and cross-ventilating barns, depending on the size and shape, but these can be tricky to fine-tune if you are not familiar with the concepts and what your barn actually needs. A quick note about cooling. Cooling usually requires a higher airspeed than ventilation, but often offers health and production benefits. Larger ruminants benefit from evaporative cooling (dousing with water or using sprinklers, then placing them under high-speed fans). Some systems will benefit from weeping walls to reduce air temperature. A partial budget can be useful for identifying how cooling will enhance or detract from your economic output, especially in dairy barns or in intensively housed animals.

A short practical ending — if you’re not sure how to ventilate your barn for the summer, more air is better, but it is best to ask for some ideas. Veterinarians, Extension personnel, and ventilation companies can often help identify your weak points and how to address them. So, open up the barn doors and enjoy the summer breeze — naturally or mechanically.