Evaluating new ventilation rate and evaporative cooling for modern swine production

Heat and moisture production (HMP) rates of animals are used for calculation of ventilation rate (VR) in animal housing. New swine HMP data revealed considerable differences from previously reported data. This project determined new design VR for swine barn and evaluated differences from previously recommended VRs. The phases of swine production evaluated included gestation, farrowing, nursery, growing and finishing. The ranges of ambient temperature and ambient relative humidity (RH) evaluated for minimum VR were -25 to 15°C at 10°C increment and 15% to 75% at 15% increment, respectively. Indoor set points for temperature and RH were, respectively, 15, 20, 25°C and 60%, 70%, 80% for all five ambient conditions. The results showed that the old VR for moisture control was 54.2%, 30.0%, 69.3%, 31.4% and 52.8% lower than the new VR in gestation, farrowing, nursery, growing and finishing stages, respectively. For hot weather conditions, there is an additional concern that the higher HMP of the pigs could increase the occurrence of heat stress if VR recommendations are not increased. Heat stress reduction by using evaporative cooling and maximum VR were estimated based on long term weather data generated by a stochastic model for locations including Sioux City, IA, Fayetteville, NC and Texas, OK. Temperature-Humidity Index (THI) was used as an indicator to evaluate animal heat stress. Effects of operating a barn with and without evaporative cooling and using different maximum VR on indoor THI were studied. The results indicated that pigs went through longer time periods and higher intensity of conditions above a critical THI threshold when not using evaporative cooling. July showed the greatest opportunity for reducing critical THI conditions using evaporative cooling, especially the period from 15:00-17:00. Evaporative cooling can substantially reduce the heat stress duration during evening through the midnight and also relieve the magnitude of heat stress during afternoon. Maximum rate of ventilation and evaporative cooling were recommended to be used jointly during July especially for gestation and farrowing stages