Canadian Poultry Magazine

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The Winter Barn

Dealing with moisture, ammonia and heating


October 27, 2009
By Carlyle Bennett Manitoba Agriculture Food and Rural Initiatives (MAFRI)

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To get your barn to behave properly in cold weather, you need to fix
problems that contribute to high ammonia and poor air circulation.

To get your barn to behave properly in cold weather, you need to fix problems that contribute to high ammonia and poor air circulation.

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Winter Challenges
To get your barn to behave properly in cold weather, you need to fix problems that contribute to high ammonia and poor air circulation.

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The turkey’s and chicken’s lungs and airsacs must be healthy to stop bacteria from infecting them. The surfaces of the respiratory system are lined by microscopic “fingers” called villi, which sway back and forth to push bacteria away from the lungs and airsacs. Ammonia can cause these villi to mat together and prevent them from functioning properly. Ammonia can also increase bacterial infection by damaging the cells lining the respiratory tract. Dust in the air will compound the damage done by ammonia. Birds exposed to ammonia are more susceptible to fowl cholera, infectious bronchitis, colisepticemia and other diseases.

It is recommended that ammonia levels in the air in poultry barns be maintained at under 25 ppm (parts per million). Table 1 describes the effects of different levels of ammonia on poultry that have been demonstrated in research trials.

For turkeys and other poultry that spend a long time on litter, ammonia can cause further problems. Ammonia that is dissolved in the water in the litter can irritate the birds’ foot pads when they walk and breast skin when they sit down. Litter producing high levels of ammonia is one of the risk factors for breast blisters in turkeys. Because litter can produce more ammonia in summer than in winter, breast blisters are sometimes higher in summer flocks.

Methods Not Requiring Heat or Ventilation:

  1. Adding fresh straw has an immediate effect on ammonia production because it forms a dry, physical barrier which prevents ammonia release into the air. The bacteria that produce the ammonia in the litter also have a more difficult time extracting carbon from fresh compared to broken down straw. If adding fresh straw helps to drop litter moisture below 30 per cent, ammonia production may be reduced even further.
  2. Dropping barn air temperature below 18°C will cause a noticeable decline in the growth of ammonia-producing bacteria and this decline will continue as the temperature is reduced even further. A temperature drop produced by running fans more frequently is more beneficial than a drop caused by turning down the temperature setting on the heaters.
  3. An acidic litter treatment can trap ammonia in the litter for one to two weeks. The ammonia is bound up as ammonium in the litter moisture instead of being released as a gas. To achieve a substantial decline in ammonia production, it may be necessary to apply double the application rate recommended by the manufacturer. Once the acid treatment dissolves it will percolate upwards into the fresh droppings, providing control even after the product has been covered over by a buildup of manure.

Top dressing the litter with a clay or cat litter type of product may provide a physical barrier similar to adding fresh straw.

If you want to test the effectiveness of a litter treatment, you can treat different sections of your barn and then measure the amount of ammonia being released in the treated and untreated areas. To measure the ammonia release, leave a canister open side down on the litter for 30 minutes and then measure the ammonia inside.

Main Causes of Wet Litter and Ammonia:

Wet litter conditions that lead to high ammonia production in the barn are commonly caused by:

  • Inadequately insulated or heated walls.
  • Poor mixing of cold incoming air with warm barn air.
  • Running minimum ventilation based on temperature instead of a fixed run rate or tying it to relative humidity in the barn.
  • Insufficient heating capacity.

The solutions to many of these problems lead to  lower heating costs.

Inlet Management
One of the basic principles of cold weather management is that you need the air to enter the barn at high speed so that it travels across the ceiling, mixing with the hot air that is concentrated there. When the air falls down to bird level, it is then warm and dry enough to remove moisture from the litter. Barn surfaces are kept warm and condensation is prevented. To get a jet of inlet air to travel across the ceiling, you ideally want air to enter the barn at an inlet airspeed of 1,000 feet per minute.

Theory vs. Reality:

While this theory is correct, several practical problems get in the way:

In many barns, half of the air on a cold day does not enter the barn through the inlets. Instead the air enters through cracks around the doors, idling fans, poorly sealed sill plates, and other sources of leakage. If the air is not entering through the inlets, it does not matter how good a job you do of managing the inlet airspeed.

The inlet air needs to enter the barn with “punch” and not just speed. Punch means that the air enters with sufficient volume that it has the momentum to travel far into the barn as well as move over any small obstacles that threaten to bounce it off of the ceiling. You must remember that the incoming air stream is constantly decaying and some of the fresh air is continually breaking away and raining down as the air stream moves across the barn. If you start with an air stream that is too small, it will decay to an insignificant airflow before it has moved very far into the barn. It will then detach from the ceiling and fall towards the floor.

To get your barn to behave properly in cold weather, both of these problems must be fixed.

Fixing the Leakage:

To get the majority of the cold air to enter the barn through the inlets, you must fix the leaks in the barn. Any fans that do not run during winter must be sealed shut. Fans that turn on and off need back draft dampers to prevent air from entering the barn when the fans stop running. Summer inlets should be insulated and sealed. Cracks at doors and door casings must be sealed or filled in. If air is leaking where the stud wall meets the concrete footing, caulking or some other sealant is required.

The best way to fix the leaks is to measure the amount of leakage and determine where the leakage is occurring. A simple leakage test involves closing all of the inlets in your barn and then turning on enough fans to generate one cfm of airflow for every square foot of floor space in the barn. For a 40’ x 250’ barn, you would turn on a 36” fan. For a 40’ x 160’ barn, you would turn on one 24” fan. You can then use an inexpensive static pressure gauge to determine how hard the fan is working to draw in the air. The more leaks in the barn, the easier the fan will run and the lower the static pressure. If the static pressure is 0.15”, you have an excellent barn. If it is only 0.05”, you have lots of work to do.

While you are running the static pressure test, you should walk around you barn and check for leaks. On a cold day, you may be able to feel with your hand where the outside air is rushing in. Preferably, you will have an airspeed gauge and you will look for spots where the air is entering the barn at 100 feet per minute or higher. You will also visually determine the size of the hole or gap to assess the size of the problem. The larger the space where the air is entering, the greater the leakage. Remember that all of the gaps around the shutters of a fan can add up quickly. After fixing the leaks that you find, test the barn again to measure your progress.

Fixing the leakage alone can have a significant impact on the estimated heating cost in a barn. On one Manitoba broiler farm, for example, the air leakage test showed at static pressure of 0.04” in one barn and 0.10” in the other. Using software developed by Mike Czarick at the University of Georgia Department of Biological and Agricultural Engineering, the heating cost for a typical January flock was calculated. The heating bill for the flock in the barn with the better score on the leakage test was estimated to be 45 per cent lower than in the barn with the poorer score.

Training the Inlet Air
Once you have fixed the leaks, you want to ensure that the inlet air does reach the ceiling. Recirculation ducts can be used to blow a stream of air that will help to pick up the inlet air and carry it towards the ceiling. Some people use scoops or deflectors that carry the air towards the ceiling. You will also want the ceiling to be smooth and obstacle free so that inlet air wants to entrain with the ceiling surface. Circulation fans can be positioned at the point where the inlet air starts to release from the ceiling and help give it a push to mix it better with the barn air before falling to the floor.

Adding Punch to the Inlet Air
Getting the air to enter the inlets at 1,000 feet per minute is not enough. You want the air to enter with sufficient volume and momentum to punch its way across the barn. Ideally, the inlets will be able to be open 1” when the fans turn on and still maintain the desired inlet airspeed. For this reason, it is often undesirable to use long, continuous inlets for winter ventilation. Systems in which half or more of the inlets can be closed during cold weather often work well. At low winter airflows, closing inlets helps to draw a significant volume of air through the inlets that remain open. The inlets will also be less prone to freezing shut.

To create the desired airflow at the inlets, you need your fans to suck in a significant amount of air. Variable speed fans are not well suited to this purpose. At low speeds, their output is highly unpredictable and very prone to wind effects. Setting the variable speed fans to run at a minimum of 70 per cent when they turn on will help them to draw in a meaningful volume of air. Fans that only run at 30 per cent will likely result in a slow, draggy airflow that does not entrain with the ceiling. A small fan that runs continuously or almost continuously may be preferable. In barns with young birds or low bird density, however, it may not be practical to draw a significant volume of air through the inlets. In that case, circulation fans are likely needed to provide air movement and mixing in the absence of an effective air inlet system.

Table 1:
Effect of litter treatment on ammonia release one week after application to wood shaving turkey litter
TreatmentAmmonia Release, ppm per hour
 Untreated 354
 Acidifier 76
 Clay Product 227


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