The focus of ventilation discussions usually revolves around heat-stress mitigation; however, winter management is equally essential for reducing pathogen loads and air pollutants that can cause respiratory disease.
Ventilation systems provide fresh air to the animal area while removing stale, tainted air that includes moisture, dust and noxious gases.
While in the summer the entire air volume in a barn should be turned over 40 to 60 times per hour, that rate declines to 4 to 8 exchanges per hour in winter.
One quick way to evaluate your barn’s air quality is to ask yourself what you smell first: silage or manure ammonia. If the answer to that question on any day is not silage, then you need to reevaluate your ventilation protocol.
Recent research shows that ammonia levels above 4 ppm can cause lung damage and increase the risk of respiratory disease, but your nose detects ammonia at 5 ppm — meaning that anytime you can smell ammonia in a cattle barn, the ventilation needs to be adjusted.
When evaluating air quality in your barn, put your nose to the same height as your animals when they are standing and lying down. Keep in mind that cows and heifers often spend over half of their day lying down, making air quality at this height critical.
Naturally ventilated barns utilize thermal dynamics to bring fresh air into the animal area and expel pathogens. Remember that warm air rises and cool air sinks.
The cool air enters through the eve opening, sinking and mixing with moisture and pathogens. As the air warms, it picks up moisture and rises, leaving the barn through the ridge or downwind side.
The lower thermal neutral zone temperature for cows is 41 F, below which sensible heat loss begins. Cows will increase their feed intake to help replace lost body heat when temperatures fall below 23 F. If a more nutrient-dense ration is provided, cows will continue to maintain body weight and production under cold temperatures.
The ventilation rate is affected by outdoor wind speed and the size of ventilation openings. During winter storms and severe cold weather, barn sidewalls should be open one inch for every 10 feet of barn width. This means that a 90-foot-wide barn should have a 9-inch side wall opening on each side.
The goal should be to maintain inside barn temperatures within 10 F of the outside temperature to limit condensation from forming on the roof and walls. Each cow produces about 14,400 watts of excess heat, roughly equivalent to a small room heater and about 30 gallons of water as respiration moisture a day.
For mechanically ventilated barns, air exchanges can be calculated based on fan speed and rated volume. Fans must be maintained throughout the winter to ensure these systems provide the correct ventilation rates. Slipping belts or dirt buildup can reduce fan efficiency and the cubic feet of air they move per minute. At near-freezing temperatures, ventilation rates should be 100-125 cfm/cow, with a minimum of 50 cfm/cow, no matter how cold it is.
Consider using baffles to guide this small amount of air throughout the barn and to prevent drafts at the inlet and fan exhaust areas. Keep in mind that small cracks throughout the barn will allow air to enter from areas other than your planned inlets.
Watching the barn environment is critical to cow health. Maintaining clean, dry stalls is crucial to helping cows retain body heat. Wet stalls or bedded pack can take heat away from the animal’s body, along with creating a perfect environment for bacteria. Managing draft on the animals is critical.
For winter ventilation, air should enter at eave height or above the cows. Air speed in the barn at cow level should stay below 1.75 mph so that the cows do not feel a draft. In calf barns, before rumen development, the maximum air speed at calf level should be 0.5 mph.
The windward side of a barn may need to be shut up more than the recommended amount during winter storms. The downwind side should be opened more to compensate for closing the windward side. A small amount of snow entering the building can be tolerated if it keeps the air in the barn fresh.
As soon as the storm passes, the barns will need to be reopened to allow fresh air in and to clear out gases and moisture. When a barn is closed for extended periods, it creates a humid environment that increases the risk of respiratory disease and traps high levels of noxious fumes.
