Layer hens in cage-free housing systems have freedom of movement, but they also encounter high levels of dust and airborne bacteria. Feed, litter, manure and bodily shedding all contribute to dust within the rooms. The mixture of dust and bacteria challenges the hens’ health and well-being, underscoring the need for a solution.
At the 2025 Dust and Disease in Egg Production virtual forum hosted by Egg Industry Center, Lilong Chai, PhD, associate professor and engineering specialist in the department of poultry science, University of Georgia, presented research on whether spraying acidic electrolyte water on the litter floor could mitigate dust and bacteria in cage-free layer houses.
“We have summarized methods that can be used to mitigate dust levels, such as electrostatic pressure ionization (EPI), filtration and biofiltration, scrubbers and manure management,” he said. “We know that spraying liquid onto the floor can control dust, but wet litter increases ammonia generation and bacteria to a very high level.”
A lab-scale study
“Before we can do a commercial-level study, we have to do a laboratory-scale study,” Chai noted. He and his team collected litter from a cage-free layer house and placed it in four dynamic-emissions chambers at the Iowa State University research laboratory.
The closed chambers included a motor with a running speed designed to mimic bird activity and generate dust. The chambers also included a nozzle to spray the electrolyte water, a gas analyzer to monitor ammonia emissions, a gas-flow meter to control inlet air, solenoid valves to control air sampling and a gas-sampling pump. The team sampled air in five locations: one in each chamber and as it exited into the room.
They administered acidic electrolyte water spray at dosages of 25 mL (D25), 50 mL (D50) and 75 mL (D75) per m2 (equivalent to 3, 6, and 9 gal. per 1000 ft2) per centimeter of litter depth.
“We know that low pH can kill bacteria and reduce ammonia, so we used phosphoric acid to adjust the liquid pH to 3, 5 and 7,” Chai explained. They also generated free-chlorine (FC) levels of 100 (FC100) and 200 (FC200) per mg/L by electrolyzing saline water.
“We ran an air pump for 20 minutes to sample the air,” he added. To measure dust levels, the team used an optical particle matter (PM) sensor; they then cultivated and incubated airborne bacteria samples.
The results
At each dosage, the water spray effectively reduced dust levels for the first half-hour post-spraying: 71% reduction at D25, 81% at D50 and 89% at D75. Measured 24 hours after spraying, the results were 57% reduction at D25, 71% at D50 and 83% at D75.
“Control was very linear up to 24 hours,” Chai noted. “Ammonia increased, of course, but D25, the lowest water dosage, had relatively low ammonia emissions. Others were higher, but still controllable.”
To evaluate airborne bacteria, Chai sprayed a D25 dosage along with FC100 and FC200 to compare the ability to disinfect the air within the chambers.
Before spraying, the bacterial concentration was about 50 to 52 ×103colony-forming units (CFU) m3. After spraying, the concentration dropped significantly within the first day to 15.7 ×103 CFU m3 for FC100 and 9.3 ×103 CFU m3 for FC200, he said. It continued to decline, and 5 days later, the bacteria concentration was 0.9 ×103 CFU m3 for FC100 and 0.3 ×103 CFU m3 for FC200.
“That is very impressive, and FC200 had higher efficacy than FC100,” Chai noted.
To measure ammonia impact, the team used sodium bisulfate added at the following rates per 1,000 ft2 at a litter depth of 2 inches:
- Control — 0 lbs.
- Low — 60 lbs.
- Medium — 120 lbs.
- High — 180 lbs.
“We placed the additive on the litter surface in the four chambers, and the litter moisture was 15%,” he said. “We replicated the experiment three times.”
Ammonia reductions for the treatments were as follows: Low, 28%; Medium, 52%; High, 79%. “These are very impressive ammonia reductions,” Chai noted.
Commercial-farm study
Moving the study to a commercial cage-free layer farm, Chai determined that spraying acidified electrolyte water and chlorine presented metal corrosion concerns, so he used tap water for dust control. “We proved in the lab that water spray can reduce dust by 60% to 70% without causing ammonia problems,” he added.
The process involved spraying 125 mL/m2 at a 1 cm litter depth in the morning, 10 minutes before the hens had access to the floor. The team tested the air before spraying and found that PM could reach greater than 20 mg/m3, and PM 2.5 could be greater than 5 to 10 mg/m3.
In the three trials, dust levels were reduced by 37% to 51%. “Not as good as in the lab setting, but there is a lot of accumulated dust in a commercial house, and 100% spray coverage is harder to achieve,” Chai said. “A 50% reduction sounds good, but it’s still not enough because the PM level could be 20, and a drop to 10 is still too high. The ideal is to get an 80% to 90% reduction.”
Ammonia levels did not increase significantly, primarily because the birds were quick to mix the top layer of litter into the rest of the material, he noted.
Other studies to consider
At the University of Georgia, Chai is continuing his research. In 2023, he conducted a bedding-management study involving three scenarios: topping existing litter with 20% new wood shavings, 20% new wood chips and a control group with nothing added. He found that the new wood chips suppressed dust by 30% to 40% for 3 to 4 weeks. “But that’s still not enough,” he added.
So, he combined the bedding options with electrostatic charging and observed a 60% to 70% reduction in dust levels.
He is also investigating a robotic system to spray acidic electrolyzed water. He believes the precise nature of robotic spraying could minimize corrosion concerns.
“In my lab, we are testing these robotics in cage-free systems to reduce floor egg laying,” Chai relayed. “We’re considering attaching a sprayer to test it for dust control.”
Take-home messages
Chai shared his perspectives from cage-free layer research and in-field experiences with the conference participants.
- Liquid spraying, such as acidic electrolyzed water, effectively controlled dust and airborne bacteria in the research-lab setting.
- Precision water spray, even without acidic or electrolyzed water, could still reduce dust levels by 37% to 50% without causing ammonia issues.
- EPI and bedding management together can further suppress dust by 60% to 70%.
- In the future, robotic systems can likely be used to facilitate more precise liquid spraying in commercial cage-free houses.
“So, there are options to consider today, but there will be more available in the future,” he said.
