Virginia dairy producers should avoid the temptation to keep naturally ventilated freestall barns too warm in winter. Cows are still productive at temperatures below 20 degrees if they are kept dry and protected from the wind, said Susan W. Gay, Virginia Cooperative Extension engineer in Biological Systems Engineering at Virginia Tech.

The key is providing proper ventilation to maintain a healthy environment for cows.

Virginia's dairy industry with about 118,000 milk cows ranks about 20th in the nation in cash receipts of more than $267 million.

"During the coldest days of winter, dairy producers are often concerned that naturally ventilated freestall barns are too cold and drafty for cows," Gay said. Some producers are tempted to keep barns warm by closing sidewall curtains. Closing sidewall curtains will create humid conditions inside the barn that may lead to respiratory health problems in cows. It also may decrease the lifespan of the structure. Evidence of humid conditions includes fog, condensation, and frost on building surfaces. However, fresh outside air is required even on the coldest winter night to replace warm, humid air inside the barn.

At 30 degrees, a 1,300-pound dairy cow produces about 30 pounds of water vapor through respiration and losses through skin. This moisture must be removed through ventilation, at a rate of 100 cubic feet per minute per cow, to maintain a healthy environment inside the barn. Closing sidewall curtains restricts this ventilation rate and allows moisture to accumulate in the barn.

Naturally ventilated barns are designed to be cold. Barn temperature should be within 10 degrees of the outside air temperature.

During severe cold weather or winter storm conditions, sidewall curtains can be partially closed to reduce airflow and the amount of sleet or snow blowing into the barn. Gay recommended that dairy producers provide a minimum opening at the top of both sidewalls that is one-half inch for each 10 feet of building width. For example, a 100-foot wide barn requires a 5-inch opening at the top of each sidewall. Sidewall curtains should be reopened to the standard 1 inch per 20 feet of barn width when normal winter weather conditions return.

Drafts should be minimized to maintain cow comfort in winter. Patching curtain holes, minimizing the space between the ends of curtains, and sealing around doors or other openings will help eliminate gaps through which wind blows.

Founded in 1872 as a land-grant college, Virginia Tech has grown to become among the largest universities in the Commonwealth of Virginia. Today, Virginia Tech's eight colleges are dedicated to putting knowledge to work through teaching, research, and outreach activities and to fulfilling its vision to be among the top research universities in the nation. At its 2,600-acre main campus located in Blacksburg and other campus centers in Northern Virginia, Southwest Virginia, Hampton Roads, Richmond, and Roanoke, Virginia Tech enrolls more than 28,000 full- and part-time undergraduate and graduate students from all 50 states and more than 100 countries in 180 academic degree programs.