Numerical Simulation of Airborne Disease Spread in Cage-Free Hen Housing with Multiple Ventilation Options

SIMPLE SUMMARY: Airborne diseases, such as highly pathogenic avian influenza, are among the deadliest threats to the egg industry and can easily cause devastating losses of poultry when severe outbreak events occur. During the ongoing transition to cage-free production, uncertainty regarding ventilation designs for cage-free facilities also exposes vulnerability with respect to disease control within facilities. To address ventilation system design and the capability of restraining internal airborne disease spread, this study was conducted to model and compare indoor airborne virus dispersal for a commercial cage-free hen house within four different ventilation schemes. A one-eighth length, full-scale, floor-raised hen house with commercial bird density was modeled to simulate the environmental conditions and disease spread under steady-state conditions inside the barn during cold weather. Analyses of the dispersion of virus particles coupled with airflow patterns were performed by visualizing contours of virus particles and air velocities at critical locations. In addition, the virus mass fraction at bird level was of particular interest when comparing and evaluating the performance of various ventilation schemes. The simulation results demonstrated that the internal dispersion of airborne virus particles was determined by indoor airflow patterns and implied the role of ventilation configuration in reducing disease spread in a poultry barn. Furthermore, valuable insights are provided for further investigations of ventilation options for cage-free hen housing. ABSTRACT: The current ventilation designs of poultry barns have been present deficiencies with respect to the capacity to protect against disease exposure, especially during epidemic events. An evolution of ventilation options is needed in the egg industry to keep pace with the advancing transition to cage-free production. In this study, we analyzed the performances of four ventilation schemes for constraining airborne disease spread in a commercial cage-free hen house using computational fluid dynamics (CFD) modeling. In total, four three-dimensional models were developed to compare a standard ventilation configuration (top-wall inlet sidewall exhaust, TISE) with three alternative designs, all with mid-wall inlet and a central vertical exhaust. A one-eighth scale commercial floor-raised hen house with 2365 hens served as the model. Each ventilation configuration simulated airflow and surrogate airborne virus particle spread, assuming the initial virus was introduced from upwind inlets. Simulation outputs predicted the MICE and MIAE models maintained a reduced average bird level at 47% and 24%, respectively, of the standard TISE model, although the MIRE model predicted comparable virus mass fraction levels with TISE. These numerical differences unveiled the critical role of centrally located vertical exhaust in removing contaminated, virus-laden air from the birds housing environment. Moreover, the auxiliary attic space in the MIAE model was beneficial for keeping virus particles above the bird-occupied floor area.