Modelling and validating the indoor environment and supplemental heat requirement during ventilation shutdown (VSD) for rapid depopulation of hens and turkeys

In response to the challenges in rapid depopulation during highly pathogenic avian influenza (HPAI) outbreaks, the United States Department of Agriculture (USDA) approved ventilation shutdown (VSD) as the last resort to stamp out infected flocks when standard methods cannot be applied in a timely manner. In this study, a model was developed to predict the indoor environment in typical hen and turkey houses during VSD, and estimate the minimal supplemental heat requirements (Hs) to raise indoor temperature to 40 °C within 30 min into VSD. The model was validated in a VSD event in a breeder house. The results show that the predicted indoor temperature and carbon dioxide (CO2) concentration agreed well the actual values measured in the breeder house. The predicted relative humidity (RH) was generally less than 5% from the measured RH. The estimated of Hs varied among poultry and housing types, and largely depends on the ambient temperature and housing air tightness. More Hs is needed at a lower ambient temperature and a higher air leakage. At ambient temperature of −30 °C −30 °C and air leakage of 0–1 air exchange rate (ACH), the predicted average indoor temperature and RH during VSD in hen and turkey houses provided with Hs could be maintained at 40–46 °C and 41%–88%, respectively. The predicted average indoor CO2 concentration is lower than 30,000 ppm. Mortalities under such environmental conditions are more likely caused by hyperthermia, rather than hypoxia. Other observations (including bird behaviour, temperature stratification, core and surface body temperature, and water consumption) during the validation VSD test in the breeder house were also reported. The newly developed model can be readily used to predict environmental conditions and Hs during VSD in other hen and turkey houses, which helps to prepare and ensure successful VSD applications during disastrous poultry disease outbreaks.