Poultry shed humidity should be monitored as regularly as shed temperature and ventilation to ensure bird health and productivity is as high as it can be, according to a poultry health expert.
Dr. Brian Fairchild, professor of poultry science at the University of Georgia, said excessive moisture is at the root of many routine health, welfare and performance issues in poultry houses.
Yet by failing to monitor shed humidity levels closely, producers are creating unnecessary health complications for their flocks.
“We need to start thinking about controlling moisture in the same way we control temperatures, because it’s just as important,” Fairchild told the ONE Alltech conference in Lexington, Kentucky.
“We have a specific target temperature in bird houses and as producers we have done a good job of measuring and maintaining that, but we need to do the same with relative humidity.”
Ideally, bird-house relative humidity needs to be between 40% and 60%. But while that figure is achieved fairly easily in warm weather when air exchange tends to be higher, during minimum ventilation periods many producers struggle.
The answer, Fairchild said, is to measure inside the house every day and adjust ventilation levels accordingly.
“If you don’t know where to start, begin with historical water consumption data from the farm,” he said.
“Once you have that, you can come up with a basic curve which will give you a starting point for ventilation which you can adjust every day depending on what’s happening outside.”
Calculating moisture balance
To help calculate ideal ventilation rates, Fairchild said the University of Georgia has developed CHKMINVENT, a moisture-balance calculator which can be downloaded as a spreadsheet or as a smartphone app.
By inputting the outside temperature, relative humidity targets, and the number and size of fans in a shed, the app can calculate how long fans need to be running to reach the correct moisture levels.
“In typical winter conditions, for example, we can work out that to remove 1 gallon of water we need to exchange 20,000 cubic feet per minute (CFM) of air, which means we need to run 48-inch fans for about 1 minute to remove a gallon of water,” Fairchild said.
“We can take this further and say that if we know the birds are consuming 1,000 gallons of water and that they retain 20% of that, we have 800 gallons that need to be removed.
“Based on our calculation, we need 5,500 CFM to maintain the moisture balance in that scenario.”
Fairchild said that one of the best outcomes of monitoring relative humidity levels is that other important variables follow.
For example, extensive University of Georgia field data shows there is a close relationship between high humidity and high ammonia and carbon dioxide levels.
“That means that doing a good job with moisture controls other air-quality variables, so if you have relative humidity levels above 70%, odds are that you’ve got poor litter and air quality too,” he said.
Maximizing house tightness
The other important element to remember is that the drier you want the litter to be, the lower the relative humidity needs to be, Fairchild added.
“So in typical winter conditions, if birds are consuming 500 gallons of water, to maintain 50% humidity you need 3,000 CFM. However, if you wanted to go to 40% you have to increase ventilation rates by 300% to 9,000 CFM.
“The problem is drier litter requires more ventilation, which means more heat and higher costs. We therefore have to be as efficient as possible and maximize house tightness to ensure heating is as sustainable as possible.”
Air that enters shed inlets is warmed by existing hot air near the shed’s ceiling, and as it is warmed its moisture-holding capacity increases, thereby lowering relative humidity, Fairchild explained.
“That means that even on a cool, rainy day, we can still remove moisture from the house.”
To check for house tightness, producers should run regular static pressure tests of 1 CFM of fan power for each square foot of floor space to identify leaks, he said.
Ideal levels of control are anything up to 0.4 square meters of leakage per 1,000 square meters, while minimum acceptable levels are 0.65 to 1.2 square meters of leakage per 1,000 square meters.
As well as addressing leaks, other changes to the shed could include using a fan with at least one-third horsepower at 100-150 feet per minute to help move air across the ceiling and floor faster and dry litter more efficiently.
“You should also maintain good drinker management to get height and pressure right to avoid splashing, distribute birds evenly to maintain litter quality, and resist turning on evaporative cooling until the outside temperature is at least 80° F,” he added.
“Each of these things can be achieved whether you’ve invested in a brand new shed or whether you’re working with a smaller, older facility. There’s no reason not to be able to work on moisture levels and make improvements.”