Importance of Dairy Barn Ventilation

Published on Fri, 06/04/2021 - 11:00am

Importance of Dairy Barn Ventilation.

 By Heather Smith Thomas.

 A ventilation system for dairy cows in barns or sheds must provide fresh air year round, but in summer it is crucial to have fast-moving air where the cows are resting, to provide adequate cooling—whether the barn is ventilated naturally or by mechanical means such as fans.  Regardless of method, the design should facilitate optimum air flow.

Even though 85% of free-stall facilities in Wisconsin are naturally ventilated, for instance, they don’t always have adequate cooling.  Wind shadows created by nearby buildings, seasonal cornfields or other obstructions, barn orientation, and other factors can limit the proper function of these systems.

Mechanical ventilation is facilitated by fans, and usually defined as either Naturally Ventilated barns where the side walls are open or Tunnel Ventilated Barns where exhaust fans are located along the width of the barn and the air flow is parallel to the feed lane.  Some barns have cross ventilation, where exhaust fans are located along the width of the barn and air flow is perpendicular to the feed lane. Some systems combine natural and mechanical ventilation—with fans over the stalls, down the feed lane with either ridge cupula fans or an open ridge to assist with removing the hot buoyant air from the barn.

Sue Hagenson, Senior Dairy Specialist with VES-Artex (a company created by the recent merger of VES and Artex Barn Solutions, based in Chippewa Falls, Wisconsin, providing technological solutions for environmental systems in agricultural facilities) says everybody talks about cow comfort, with most conversations centered around free-stall dimensions, etc. and not necessarily looking at keeping the cows cool.  Her company focuses on keeping them cool so they can stay lying down longer.  “People need to understand the key role of a fan,” she says.

What you need will be based on the cow’s stage of lactation or whether she is dry, the climate, and the building she is in.  “For many years, fans were considered the least important aspect, but now the industry has become better focused on why they are needed.  Even just a few years ago people thought that just about any fan would work, without understanding the function fans and a fan’s capability,” she says.
There has been some good research from a number of universities demonstrating the impact heat stress has on cow productivity and the positive impact of correctly ventilating and cooling cows.  “What is surprising is there is still a perception that any air blowing over the cow is good enough” she says.

“When putting a ventilation strategy together, I look at the barn type, where the farm is located in terms of climate and what the cow needs on the worst day of the year.  In most cases I want the air moving at a rate of at least 3 meters (about 9.8 feet) per second, and that target airspeed must be down where the cow is lying—not way up above her,” says Hagenson.
That way we can increase the cow’s lying-down time.  “Cows typically lie down approximately 12 times per day, and we want them to lie down for as long as possible during those periods.  I’m always focusing on getting the target air speed between half a meter (1.6 feet) to a meter (3.2 feet) above the bed.  This is very important, and this target air speed needs to be underneath the next fan.  That way I get good air speed coverage in all free-stall,” she says.

“When ventilating an open pack, I space the fans so I can get a wall of air moving down the pack to ensure the cows are evenly cooled throughout the pack.  The air needs to move out of the barn fast enough to maintain good air quality as well, ensuring there is no moisture, pathogens or noxious gas build up,” she explains.

“Thus the size of the fan is very important.  The fan needs to be able to cover the width of the free-stall and throw the target air speed to the required distance.”  Fan selection and spacing is always based on the climate; the humidity and temperature.

“We know that if we can get a cow to lie down for even one more hour per day, we’ll see an increase in milk production.  It also means that she will want to eat a little more.  If she lies down for a longer time, she is resting her feet (reducing the incidence of lameness) and she’ll have a better opportunity to get in calf because she is comfortable.  If there are cows standing up in the barn and/or bunching on a warm day, we need to know why.”  Is it because of the condition of the free-stall, or because the cows are trying to cool themselves?

“I liken a cow to a furnace; she produces a massive amount of body heat.  When she lies down, she accumulates heat at 0.5 degrees C (1 degree F) per hour as there is not as much surface area to dissipate that body heat, and it takes twice as long for her to remove/dissipate that same amount of heat,” says Hagenson.  
When putting a ventilation strategy together it is always important to understand all of those things.  “A little 55-inch basket fan with half-horsepower motor will not move air very far in terms of length and width from the fan.  If I have lots of little fans in my barn, I need more outlets and I am spending more time maintaining fans, whereas if I have larger fans I get better coverage with fewer fans.  Then I am likely reducing my operational costs as electrical usage will probably be less,” she says.

Every day is different, and as you come into the shorter days of the year (if you are lucking enough to have 4 seasons) having bigger HP motors with a variable frequency drive allows the motor speed to be adjusted, based on the Temperature-Humidity Index in the barn.  “As the temperature cools down, I don’t have to run the fan as fast and I’m not using as much electricity.”
In many areas, rural or agricultural, power is not very expensive, but a dairy is always looking at ways to be more efficient and sustainable.  There is good payback when you are in a climate that varies throughout the year.

Another important aspect is to be able to effectively cool cows when the environment gets too hot for the cow to effectively cool herself.  When ambient temperature exceeds 21 degrees C (70 degrees F), a high percentage of the heat the cow dissipates is through evaporative cooling.    

“I want to be able to cool her, and the most effective way to do this is with water.  This can be done through directly applying water to the cow’s body. This is typically done by soaking her at the feed lane.  Research shows that if you have fast air moving (about 6.7 mph) down the feed lane and soaking once every 5 minutes, you have the ability to rapidly cool her down, since wetting a cow increases her conductive heat exchange as well.  

The milking parlor holding yard is a priority area for cooling.  Not only does moving from the barn to the parlor increase the amount of heat a cow generates (with exercise), it is compounded by the high animal density, and the cows “heat up” a lot faster.  “Without cooling, the cow’s body temperature increases by 1.6 degrees C (2.88 degrees F) within 20 minutes of the cow entering the holding yard.  So we need to apply the same cooling principals, with air speed of about 6.7 miles per hour, and soaking.  The objective is to avoid having heat stressed cows enter the milking platform,” she says.

Equally important is the ability to maintain good air quality.  Along with the heat generated by the cows, there are some noxious gases, plus the added moisture and pathogens—which all work to create an undesirable microclimate.  “All of this equates to additional stress just before we ask those cows to step onto the platform and let down their milk,” says Hagenson.

In drier climates we can indirectly cool the cows through high-pressure fogging, used  in combination with high velocity fans  “We can use one or multiple stages of fogging, based on what the climate is like and the farmer’s objectives.  High-pressure fogging cools the air around the cow, creating a temperature difference between the cow and her environment whereby the rate of heat transfer from the cow to the environment increases.  Plus, the cow is breathing in the cooler air, which can also help cool her.  One of the challenges is that high-pressure fogging adds additional moisture and heat into the environment, therefore it is important to have fast-moving air to remove the moisture from the building, maintaining good air quality.”  

The cow must always be the primary focus because she is the “breadwinner” so to speak.  “It is unfortunate that many people consider fans just an expense rather than an investment or necessity. My passion is to come up with a strategy or solution that fits the farm, fits the environment, and then have the satisfaction of seeing the improvements after we put these systems in,” says Hagenson.