Recent temperature fluctuations have presented challenges for calf raisers across the Midwest and many farms have seen an uptick in respiratory issues. While calf hutches are often referred to as the gold standard of calf housing, the need for intensified management during the most inclement winter weather has deterred many from this option.
The result is more calves being raised in barns or other housing with greater protection from the elements. Many of these structures rely on natural ventilation to provide clean, fresh air to the calves. This works well in the summertime; however, as doors, windows and curtains are closed in the winter, providing sufficient air exchanges to keep calves healthy can be challenging.    
Whether using mechanical or natural ventilation, the goal is to provide fresh air uniformly at the calf level throughout the housing facility so all calves receive an adequate quantity of draft-free, fresh air. The source of this fresh air is the ambient outside air. Therefore, proper ventilation means taking outside air and evenly distributing it throughout the barn. 
The goal of a ventilation system is to control heat and moisture within a shelter and remove other gases and pollutants. In the winter, the focus needs to be on controlling and removing excess moisture produced within the barn. Generally, cold temperatures within the barn do not affect calf health during the winter. However, damp and wet air in the barn during the winter will negatively affect calf health.  
It is important to remember that calves are constantly producing water vapor as they breathe. Researchers at Penn State University estimate that, at 37 degrees, a calf produces 1.25 ounces of water per hour. While this may not seem like much, it equates to almost 2 pounds of water per calf per day that needs to be removed from the barn. 
One issue with winter ventilation is the physical property of cold air. Cooler air cannot hold nearly as much water vapor as warm air. If air within the barn is not constantly replaced with fresh outside air, this moisture can begin to condense on surfaces such as the floor, ceiling and pen dividers. This additional moisture can create an ideal environment for pathogen growth and lead to disease outbreaks and transmission.  
The goal for calf barn ventilation in wintertime in the Midwest is to have a minimum of four air exchanges per hour. Good ventilation not only provides the needed air exchange, but it also provides good air distribution throughout the barn. This can be a struggle with the lower ventilation rates of winter, leading to areas of the barn with air that is stale and wet while other areas have good air quality.  
Proper air distribution can be provided by a positive pressure ventilation system. A well-designed positive pressure system will deliver fresh air at the calf level without creating a draft.
For mechanically ventilated calf barns, work with the consultant who designed the system to stage the fans for adequate air exchanges depending on both the indoor temperature of the barn and the outdoor temperature.
Proper nutrition needs to be provided to calves in the wintertime as additional calories are needed for maintenance. Calf jackets will help calves retain the body heat they produce. Good bedding use and management is needed to provide insulation as calves burrow into the pack in cold temperatures. It also helps the calf maintain a dry and buoyant hair coat. Frequent cleaning and removal of soiled bedding can be an efficient method to keep air fresh and reduce ammonia concentration, especially in older calves.
Work with your calf team and advisors if you feel ventilation is not adequate in your barn regardless of the season. Focusing on ventilation in the winter months can result in improved health and performance of calves.  
Barry Visser is a nutritionist for Vita Plus.