PERHAM, Minn. – Summers in the Midwest are unpredictable, with extreme weather fluctuations affecting cow comfort and health on dairy farms throughout the region.
    The concern for animal welfare does not end when the sun begins to set sooner. In fact, the same challenges with temperature and moisture are present throughout the winter months, and the solution lies in proper ventilation.
    “Being in the Upper Midwest, we get a wide temperature range; so how do we manage that?” said Kevin Janni, professor and engineer with the University of Minnesota.
    Janni gave a presentation on proper barn ventilation during a Moo University workshop Jan. 14 in Perham, Minn.
    As cold weather sets in, barns are buttoned up; but it is crucial ventilation through the facilities remains to deter lingering stale air and the build up of unwanted moisture.
    “While a higher temperature in the barn will keep manure from freezing, it also raises relative humidity and increases the risk of pneumonia in the herd,” David W. Kammel said.
    Kammel, a professor of biological systems engineering with the University of Wisconsin-Madison, has worked with the state’s extension as an expert in livestock housing since 1985.
    During the winter, farmers should manage the barn climate to the point when manure is likely to freeze and adjust accordingly with weather conditions and the needs of the animals.
    Naturally ventilated barns provide a temperate climate conducive for animal welfare nearly all year-round. However, winter cold snaps make them less efficient, and for this reason mechanically ventilated barns are growing in popularity.
    Steve Driessen and his family updated their 1991 naturally-ventilated freestall barn to a tunnel-ventilated system about five years ago.
    “Before, we were always dealing with frozen teats and frozen manure,” Driessen said. “Now, there are no frozen teats and the manure doesn’t freeze either.”
    The Driessen family milks 200 cows near Porter, Minn.
    Since renovating the housing facility, the Driessens have noticed the barn remaining consistently warmer. However, to ensure proper airflow, vents are open on the sidewalls to let fresh air in, as well as a vent on top of the barn to let warm air out as it rises through the building.
    Oftentimes, the trickiest part of managing any housing facility is maintaining a temperature in which the animals can thrive.
    Within a herd, the temperature range in which an animal is comfortable varies based on age, Janni said.
    The thermal neutral zone for cows is between 5 and 77 degrees Fahrenheit. For calves, they are comfortable at temperatures ranging between 50 to 77 degrees for those less than 1 month old and 32 to 73 degrees for those older than 1 month.
    Outside temperatures in the Upper Midwest can vary from minus 20 degrees to more than 100 degrees, so maintaining a consistent climate in the barns is essential.
    As a benchmark, naturally-ventilated facilities should remain about 5 to 10 degrees greater than the temperature outside to provide minimum air exchange to prevent manure freezing, yet a quality air environment for the cows, Kammel said.
    “We think the temperature needs to be more than it really does for cows,” he said. “As long as they’re out of the drafts, they can handle it. The key is to manage temperatures to the point where manure would freeze as best as possible.”
    There are four components of indoor temperature to consider when determining if the barn is adequately ventilated – relative humidity, temperature-humidity-index, air velocity and ammonia levels.
     Relative humidity and dew point temperatures both benchmark points in which moisture is in the barn. While both values indicate moisture in the air, relative humidity is the percent saturation at a given temperature. Once the relative humidity reaches 100 percent – the air is entirely saturated – then the dew point is reached.  
    “Personally, as an engineer, I prefer to work in dew point temperatures,” Janni said. “I like to keep relative humidity at a point where no condensation or frost will form in the barn.”
    Farmers should aim for 50 to 80 percent relative humidity in their housing facilities.
    If relative humidity and dew point are not managed with effective ventilation, moisture accrues and will pose health risks for the animals.
    “I was in a calf barn with a metal roof and no ventilation,” Janni said. “The ceiling was frosty in the morning, and as the sun rose and heated the roof, the frost melted and it was raining on the calves.”
     Adequate air velocity should measure at 60 feet per minute at the calf level. In tunnel-ventilated and cross-ventilated barns, farmers should aim for 528 feet per minute, or 6 miles per hour, whereas the inlet air velocity should be between 800 to 1,000 feet per minute.
    Aside from numeral benchmarks, the animals within the barn will also show signs of adequate airflow. Respiration rates, milk production and cost lost in milk production are all indications something is not right in the barn.
    “If animals are exposed to high humidity for a long period of time, it can be detrimental to their health,” Kammel said.
    Janni agreed.
    “Monitor the cow with the highest production as a baseline,” he said.
    Visual cues in the barn, such as fog or wet trusses, may also indicate there is not enough ventilation.
    “If the steel surfaces are dripping or frosted, then the humidity is too high and the materials are too cold,” Kammel said. “Same thing if it’s foggy in the barn. You need to open up inlets of the curtains and bring in an exchange of cold, dry air.”
    Janni agreed.
    “Air is lazy; it takes the easiest path,” he said. “When trying to manage ventilation with baffles, avoid open aisles or the wind will all go there.”
    Damp conditions also cause added wear on the facilities, creating weak points in the structural soundness of the barn and impacting the building’s longevity.  
    Wintertime poses its own set of challenges, regardless of barn design.
     “Everyone brags about cow comfort in the summer and how you don’t lose milk [with tunnel ventilation], but no one talks about the winter,” Driessen said. “The barn is a lot darker and it does get warm.”
    Driessen also mentioned that while they no longer see frozen teats, some stalls become filled with snow when the north wind hits the barn.
    “We’ve made an old barn work with a new system, but it’s tricky,” Driessen said.
    In the Upper Midwest, there is no easy way to deal with cold temperatures that is conducive for both animal health and farm management.
    “Cows can tolerate stress from poor air quality for a little while, but eventually it will come at a cost,” Kammel said. “The options are to suffer through frozen manure for a few days or treat pneumonia later on. You have to be ready to deal with manure build up in a different way so that ventilation is at its best for cow health.”