By Xinjie Tong and Lingying Zhao
The Ohio egg production industry is a significant economic sector in the state and is responsible for creation of 12,503 jobs and $438 million in annual earnings. Technology advances in egg production facilities over the past decades have enabled very efficient operations of large-scale layer houses, that can typically host 100,000 to 250,000 hens with stacked cages, automated manure-belts, feed and water delivery, egg transport, and mechanical ventilation systems. In these larger layer houses, ventilation plays a crucial role in maintaining a proper indoor air conditions and for disease control for hen health and efficient egg production. However, it has been a challenge to achieve the comfort and health standards with existing ventilation systems. At The Ohio State University, an innovative ventilation system has been designed at the air quality and bioenvironmental lab, which can potentially improve indoor environment and limit disease outbreaks in layer houses.
The most commonly used ventilation systems in layer houses are tunnel ventilation and cross ventilation. With a cross ventilation system, air enters a layer house through air inlets under the eaves or on the ceiling and exits through exhaust fans on side walls. It creates relatively uniform airflow inside the house, but is not able to effectively remove heat produced by hens in the summer. To abate heat stress, tunnel ventilation system has been widely adopted in layer houses, with which fresh air enters a layer house from one end of the house and is exhausted by fans located on the other end of the house. The tunnel ventilation provides a wind chill effect with high-speed air flow across animals and thus can make them feel cool in hot weather conditions and effectively alleviate heat stress in summer. As air travels from the inlets to the exhausts of a layer house with the tunnel ventilation system, it absorbs heat and moisture generated from hens. One big drawback of tunnel ventilation systems is that it results in large gradients of air temperature and relative humidity, air pollutant concentrations along the airflow pathways, and will make the air cool and dry near the air inlets but hot and moist near the air outlets. This non-uniform thermal condition is not desirable because it not only puts hens near outlets at higher risks, but also results in differentiation in hen performance, such as various sized eggs. It is therefore imperative to fully understand the thermal environment of large-scale commercial layer houses and develop an innovative ventilation system in order to manage heat stress problems accordingly and effectively.
Heat stress problems in layer houses
Heat stress is a common problem in layer houses because hens stocked in high density form intensive heat sources and the state-of-the-art ventilation system, tunnel ventilation, still cannot uniformly remove heat. Poultry are homoeothermic with a core body temperature maintained at 41.2 degrees C to 42.2 degrees C by thermoregulatory mechanisms in a comfortable environment. As the indoor temperature rises above the poultry comfort zone during hot summer months, hens start experiencing heat stress, where they usually spend less time feeding and moving, and more time drinking, resting, and panting. Egg production is also impaired under heat stress (i.e., annual losses of $61 to 98 million nationwide) through decreased egg production rate, reduced egg quality, and increased hen mortality. Heat stress problems will be further worsened due to increasing events of extreme temperature and heavier precipitation.
Disease outbreaks and virus transmission in layer houses. Disease outbreaks are another big threat to the poultry industry. In 2015, the highly pathogenic H5 avian flu infected about 57 million birds in the U.S., resulting in a disastrous loss to the layer and turkey industries. Because the flu spread quickly, researchers suspect that the viruses were possibly airborne, meaning that their transmissions can be possibly driven by airflow.
With the current ventilation systems, air mixing causes concerns about possible disease transmission. Once a hen has the virus, the ventilation airflow will transport the air polluted by that hen, and pass through many other hens located in different areas of the house before being removed via exhaust fans. In other words, the mixing ventilation possibly facilitates the transmission of viruses among hens and fastens the spread of the disease.
Development of a new ventilation
To reduce economic losses due to heat stress and disease outbreaks, we are developing an upward airflow displacement ventilation (UADV) system for commercial manure-belt layer houses. In this new system, fresh air is uniformly supplied from air ducts located beneath the cages; it directly reaches hens and is heated by hens; the heated air will then escape the cages and flow upward in the aisles due to the buoyancy effect and suction caused by exhaust fans installed on the roof; air is finally exhausted out of the house through these exhaust fans. With this new ventilation system, an upward airflow can be formed inside the house and the polluted air traveling upward in aisles will be directly removed by exhaust fans on the roof without passing through other cages. This ventilation design allows for the shortest pathways of contaminated air and provides efficient removal of heat, moisture, air pollutants, and viruses compared to existing tunnel and cross ventilation systems.
Performance of the new ventilation system
The performance of the new UADV system was preliminarily simulated using a Computational Fluid Dynamics (CFD) model developed by an Ohio State University research group. Using CFD models, indoor thermal conditions and disease transmission were simulated under different weather conditions with both the new UADV system and the existing tunnel ventilation system. It was found that the new UADV system provided more uniform thermal conditions with less heat stress compared to the existing tunnel ventilation. By using the new UADV system, heat stress at a danger level could be reduced from 8.7% to 0.7% in summer and cold stress could be reduced from 18.3% to 5.8% in winter. The new system also reduces the disease transmission from 29.8% to 2.7% in summer and from 61.4% to 44.3% in winter in the presumed scenario.
Researchers, Dr. Lingying Zhao, an extension engineer and professor, Xinjie Tong, a Ph.D. student, and Dr. Sewoon Hong, a postdoctoral research associate at The Air Quality and Bio-Environmental Engineering Lab (AQBEL) of The Ohio State University, have submitted a provisional patent application for this new ventilation design. Further efforts are needed to test the UADV system in commercial laying hen farms. Any feedback and inputs from poultry farmers about the new ventilation systems will be very much appreciated.
In summary, maintaining a comfortable and safe indoor environment of layer houses is a necessity, but a challenging task that cannot be fulfilled by the existing ventilation systems. The heat stress and disease outbreaks have caused significant economic losses. Ohio State researchers have developed an innovative upward airflow displacement ventilation (UADV) system for abating heat stress and limiting disease transmission among the hens. It can effectively improve uniform thermal conditions in layer house for abatement of both heat and cold stress. It also has the potential to limit pathogen transmission in layer houses. Further research is needed to test the UADV system in commercial laying hen farms.
Xinjie Tong, Graduate Research Associate, Department of Food, Agricultural and Biological Engineering and Lingying Zhao, Professor and Extension Ag. Engineer, can be reached at email@example.com. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences.