The main purpose of winter ventilation is to get rid of excess moisture produced by the birds so that relative humidity stays within acceptable levels (say, 40 to 70%). However, with reduced ventilation, there is moisture build-up in the house. When this humid and warm air mass contacts cold surfaces (e.g., uninsulated concrete walls or metal inlets, or portions of the ceiling where insulation material has shifted), water will condense and then drip down to the floor and wet the litter.

When the litter is wetted, there is increased biochemical activity in the litter and ammonia production increases. In winter, with wet and old litter,ammonia concentrations in excess of 50 parts per million (ppm) are not uncommonly. Such high ammonia levels can attack the eyes and respiratory system of the bird and weaken its immune system in the long run. High ammonia levels can also cause breast blisters and foot pad burns.

During the growout cycle, if high humidity and/or high ammonia levels are observed in the house, the ventilation rate needs to be increased. How much to increase the cold weather ventilation rate (for a particular size of birds) will depend on how much stale air the minimum ventilation fans are removing.

Integrators provide guidelines on how long to run the fans (say, 1/2 min. out of 5 min.) depending on the size of birds. These guidelines are based on the size and number of birds, capacity and number of fans, and weather (cold, mild, or hot).

Weaver¹ suggests a cold weather ventilation rate of 0.4 cfm/lb of bird; so, 20,000 1-lb birds need about 8,000 cfm of ventilation. When the integrator provides ventilation guidelines to the producer, the integrator assumes a certain airflow rate through the fan. However, with wear and tear, the fan's performance deteriorates and it cannot pump out the same airflow rate as it could when it was new.

For example, a clean 36 in. fan with clean shutters and guard (with a static pressure drop of about 0.05-0.10 in. water column) may pump out 9,000 cfm while a dirty fan (say, static pressure drop of 0.15 in.) may pump out only 7,500 cfm! In 48-in. fans, airflow rates can be reduced by as much as 30% with worn, loose belts compared with wellmaintained belts.

Hence, with birds in the house, apart from cleaning the shutters and guards (as much as possible), the producer should increase the ventilation in small steps, by trial and error, to a point where moisture and ammonia are manageable.

Of course, the service person should be notified of these changes, ammonia measurements should be made and the situation should be monitored. If the house gets too dry (and dust levels build up), reduce the ventilation in small steps.

¹Weaver, W.D., Jr. 2002. Fundamentals of ventilation. In Commercial Chicken Meat and Egg Production, 5th ed., editors D.B. Bell and W.D. Weaver, Jr. Kluwer Academic Publishers, Norwell, MA.

February 2007