As we come into the fall season, poultry growers will find themselves transitioning between the heat removal needs of summer flocks to the moisture control needs of winter ventilation. One exception is growers with solid sidewall houses; they have less variation since there really is no seasonal variation and houses should be prepared the same in January as they are in July. Fall temperatures particularly in the southeast can be cool at night but high enough to require heat removal towards the afternoon. If growers don’t carefully focus on directional air flow and relative humidity in the cooler times of the day, house moisture can increase to the point where young chicks become too cool and litter begins to cake. There is a temptation to restrict ventilation too much in the evenings without paying attention to relative humidity.
Moisture control is the main role of minimum ventilation strategies. Because of that, the most important factor in monitoring air quality and ventilation success during the cooler parts of the day is relative humidity. Poultry houses are designed to be ventilated for relative humidity and moisture control. In cold weather, growers tend to under ventilate and slick over the litter. By controlling ammonia with an acidic litter treatment such as PLT® litter acidifier, houses can again be ventilated properly for relative humidity.
Impacts of Relative Humidity
The best time to measure relative humidity is in the mornings during brooding. After 14-21 days the need to vent heat from the house becomes the dominant factor in ventilation regardless of the time of year. It is important to keep relative humidity between 50-70%. Above 70% for more than 24 hours and the house will begin to become damp and the litter will slick over. Once this happens, the damage is done and difficult to correct. The litter will begin to generate greater amounts of ammonia and this, combined with the high humidity, will burn up a litter treatment within a matter of hours and cause a grower to burn more fuel later on to rid the house of excess ammonia.
The increase in litter moisture will also allow for a bloom of bacteria, fungi, viruses, and coccidia, which can overwhelm even the best health programs. Drying the litter out then disseminates a large number of fungal and Clostridial spores throughout the house. If the relative humidity is below 50%, the dry air will begin to dehydrate the young chicks and will dry out their mucous membranes. This makes them more susceptible to respiratory disease and is similar to what happens to humans on a long airplane trip.
Tools to Measure RH
The easiest way to measure relative humidity is with a simple digital humidity meter of hygrometer. These are available from a large variety of sources and range from $15 to $100. Simply place the hygrometer on the feed line when you enter the house in the morning and let it sit for 10-15 minutes and take a reading. The hygrometers should not be left in the house because they easily become clogged with dust. If the relative humidity is above 70%, increase fan time by 15-30 seconds. If the relative humidity is below 50%, decrease fan time by 15-30 seconds. It’s that simple. Stationary humidity sensors connected to the house’s controller do not work well for a number of reasons and are not recommended.