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Ventilation in Dairy Farms

Source: Allison Wright, University of Minnesota Extension Intern - McLeod & Meeker Counties

During the hot summer months, one key practice is having good ventilation on your dairy farm. Numerous studies have shown that having poorly maintained fans can lower ventilation levels by 40-60%, according to the University of Minnesota. Let’s dig deeper into air exchange, different types of ventilation, cooling systems, and why ventilation is important. 

Air exchange refers to the number of times the air in a certain area changes per hour. In a dairy barn, the target air exchange rate is 60 to 90 changes per hour. This can be implemented as natural or mechanical practice. 

Air velocity is the difference between air density and differential pressure. This is relevant to ventilation because increasing the air velocity in barns will get rid of still heat by the cattle. The University of Minnesota gives the example of, at a THI (Temperature-humidity index) of 75 and an airspeed of three miles per hour (mph), a cow producing 100 pounds per day would be expected to have a respiration rate of around 68 bpm (mild heat stress). Increasing the airspeed past the cow to ten mph would lower her respiration rate to 57 bpm (no heat stress).

Dairy farms are all shapes and sizes which is why different ventilation practices and systems can be adapted in different ways to fit each dairy farm’s needs. Ventilation affects more than the cows' ability to feel heat stress, this also influences fly control, bed pack microbial growth, and the worker environment. There are three different types of ventilation: tunnel ventilation, cross ventilation, and natural ventilation. 

Tunnel Ventilation,

  • Airflow starts from one side of the barn and brings the air to the opposite side of the barn. 
  • Size of fans needed depends on the size and length of the barn. 

Cross Ventilation,

  • Airflow starts on one side of the barn and brings the air through to the other side. 
  • Used to keep the airflow at cow level, and increase the air velocity at cow level. 

Natural Ventilation, 

  • Used mainly by the wind in hot weather. 
  • Fresh air enters through the open sides of the barn, with no fans.

Whether in a tunnel or cross ventilation system, maintaining clean fans is essential to maximize the efficiency of the fans. A stiff brush will remove dust and dirt from many fan parts. Compressed air finishes the hard-to-reach areas. Never use water to clean fans.

A common practice for free stall barns is adding a water soaker system as well as a ventilation system. There are two types of water soakers: high-pressure misters and low-pressure sprinkler systems. The difference between these two is either a misting or soaking outcome based on the water droplet size. 

A high-pressure mister will lower the temperature around the cows by adding fine droplets of mist into the air, but it will increase the relative humidity of the barn. This method is recommended for drier climates. 

In contrast, low-pressure sprinklers use water droplets to directly wet the cow. As the water is evaporating off of the cow, this will cause the cow's body temperature to cool. With an added benefit of pulling heat away from the cow's skin directly. This outcome is intensified by a direct breeze from a ventilation system in the free stall. 

The graph shows the correlation between temperature range and soaking frequency time from the University of Madison, Wisconsin Extension. 

Temperature Range (F) Soaking Frequency (min)
70 - 80 15
81 - 90 10
>90 5

The table shows the positive relationship between an increase in temperature and a shorter soaking frequency between soaking. The soaking frequency is more frequent because the water will evaporate faster off the cow on a higher temperature day. 

For more information on ventilation practices, contact your local extension office. For information about this or any livestock-related topic, please reach out to your local Extension Educator. Residents in Wright, Meeker, and McLeod counties can email ande9495@umn.edu or call 320-484-4303. 

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