Cooling effects of spraying combined with tunnel negative pressure ventilation in enclosed feedlot barn

Abstract: Spraying combined with the tunnel negative pressure ventilation to cool animals is widely used in swine and poultry house, but it is rarely used in feedlot barn. The objectives of this study were to explore the operation mode of spraying combined with the tunnel negative pressure ventilation in enclosed feedlot barn and compare its effects on environmental factors, physiological indexes and growth performance of beef cattle with the efficient cooling method that spraying combined with fans in open feedlot barn in summer in Southern China. Jinjiang Yellow Crossbred Cattle (average body weight 273.4 kg) were fed in the treatment and the control barn for 30 days. In the treatment barn, low pressure two-stage atomizing sprayers and fans were installed in the automatic control rolling blinds barn, and the system cooling the beef cattle by spraying combined with the tunnel negative pressure ventilation. In the control barn, high pressure atomizing sprayers and fans were installed in the open barn to cool the beef cattle by spraying combined with fans. Before the animal study, four comparison intermittent operation modes (A: 5 min on and 5 min off, B: 5 min on and 10 min off, C: 10 min on and 5 min off, D: 10 min on and 10 min off) were conducted to determine the best operation mode of spraying combined with the tunnel negative pressure ventilation. According to the changes of indoor temperature and relative humidity and the variations of temperature-humidity index between the four operation modes, the spraying in the treatment ran intermittently 10 min on and 10 min off between 9:00-12:00 and 16:00-19:00, and 10 min on and 5min off between 12:00-16:00. Meanwhile, the spraying in the control ran intermittently 5 min on and 10 min off between 09:00-19:00. Then, the data of environmental factors, rectal temperature (Tr), lying rate (LR), respiration rate (RR), average daily gain (ADG) and economic benefits were collected. The results showed that, compared with the control barn, the average air temperature was decreased by 2.2 ℃ (P<0.01) while the relative humidity was increased by 11.3%(P<0.01) in the treatment barn. For the cattle, spraying combined with the tunnel negative pressure ventilation can reduce its Tr by 0.26 ℃ (P<0.01) and improve its LR by 12% (P<0.01) than spraying combined with fans in open feedlot barn, but there was no significant difference on its RR. Compared with the cattle in the control barn, the ADG of the cattle in the treatment barn was increased by 0.19 kg/d (P>0.05), and gross profit of the treatment barn was increased by 72.67 Yuan per head per month. In conclusion, the spraying combined with the tunnel negative pressure ventilation in enclosed feedlot barn had a significant effect on improving the environment and the performance of the beef cattle, and it contributed to relieve the heat stress of beef cattle and improve its production performance.