Ask the Expert: Managing Curtains in the Fall
Posted on November 9, 2012 in Starting Strong - Calf Care
By Dr. Becky Brotzman, DVM, University of Wisconsin-Madison School of Veterinary Medicine associate outreach specialist, and Dr. Ken Nordlund, DVM, UW-Madison School of Veterinary Medicine clinical professor
Q: With the huge temperature swings in the late summer and early fall, I am always wondering how to handle the curtains in both my nursery and transition barns. What’s a good gauge for managing curtains in various weather conditions?
A: Managing curtains on calf barns and adult cow barns alike can become tricky, especially in spring and fall when the air is often cool and damp with intermittent periods of warm weather. Unfortunately, there aren’t any well-researched rules for managing curtains, but we can apply some basic principles to make sure the air in our calf barns is free and clear of problems this fall.
Natural ventilation in calf barns is primarily achieved by capturing wind through an opening in the eave or curtain sidewall, which should be at least 1 inch on each side of the building for every 10 feet of building width and potentially at least half of the sidewall.
The minimum winter ventilation rate for barns is four times per hour and mild weather dictates closer to 15 air changes per hour. It may be an interesting back-to-school exercise in math and geometry for your kids to calculate the barn volume and ventilation need. Measure the wind speed at the windward sidewall of your calf barn, and then determine the cross-sectional area and length of the curtain opening to find the minimum opening height. Remember, that number will change constantly as the direction and speed of the wind changes.
However, we do need to balance ventilation with keeping calves warm. A calf’s thermal neutral zone (the ambient temperature range in which calves don’t expend additional energy to cool off or stay warm) is 50 to 78°F at birth and 32 to 73°F at one month old. A starting set of guidelines for a nursery calf barn might be as follows:
- Below 40°F: Curtains should completely cover the sidewall. A well-designed supplemental positive pressure ventilation system should be installed and run continuously throughout the year to provide the minimum ventilation rate regardless of curtain position, while not creating a draft on the calves.
- Between 40 and 75°F: Adjust the top curtain opening “as needed,” but what that exactly looks like depends on wind, rain and sun.
- Above 75°F: The curtains should be completely open.
Older calves have a lower critical temperature of around 20°F, so the above general guidelines should be adjusted downward accordingly. Wet, dirty and matted hair coats on calves will not insulate as well as clean, dry coats. These calves will require more energy to stay warm before the mercury drops below their normal lower critical temperature, and require changing the above guidelines as well.
In the summer, we use the term “humid” for “damp,” but either way we’re talking about water in the air. While curtains can be adjusted to protect calves from cold wind and keep some warmth in the barn, humidity cannot be kept out of the barn effectively with curtains or ventilation systems. Calves and bedding can certainly be kept dry during rain and snow by raising the curtains, but this will not prevent moist air from getting into the barn. Actually, we can easily increase the humidity within the barn by raising curtains on damp days due to lack of ventilation and moisture added to the air from urine and spilled water and milk. Dampness, apart from actual rain or snow, is not a good reason to close the curtain on a calf barn in spring and fall.
Many people have spent a lot of time and effort trying to define curtain management in different conditions, but find it difficult to accommodate the many combinations of weather and preferences that could exist. Mechanical controllers are very helpful, automatically adjusting curtains in relation to temperature. Fancier systems also account for wind and even precipitation. While a few mismatched weather events require an override of the mechanical system, automatic curtain openers can help decrease the chore of opening and closing curtains and help ensure calves get the fresh air they need. According to the Madison-area NRCS wind rose plot from January, winds can be calm or from a non-prevailing direction much of the time. A supplemental positive pressure ventilation tube system will also be important for these periods of time.
Instead of buttoning up the calf barn from October through March in attempt to keep calves warm, provide deep, fluffy bedding that allows calves to bury their legs, in addition to adequate nutrition and calf jackets as needed. While covering the pens with boards or other materials can keep cold air from falling from eaves into the calf pens, the covers also prevent ventilation and result in extremely high levels of airborne bacteria and other pollutants around the calf. Alternatively, set calf pens away from the curtain sidewalls by about three to four feet to keep colder air from falling directly onto calves as it enters the building through the curtain opening. This same concept can be applied to group nursery barns to help keep calves spread out in the pen and not hovered together to keep warm in the presence of a draft.
For more information on calf barns, see The Dairyland Initiative website at http://thedairylandinitiative.vetmed.wisc.edu.
Starting Strong - Calf Care