Comparing fogging strategies for pig rearing using simulations to determine apparent heat-stress indices

Strategies to reduce the apparent heat-stress indices inside a growing pig building were compared. Two fogging strategies were studied, fogging with the necessary water evaporating to give the same: (i) duration of heat-stress, ‘FDuration’, and (ii) intensity of heat-stress, ‘FIntensity’, as when using evaporative pads, ‘EPads’. For the whole 5-month period (May–September) under Greek summer conditions strategy ‘FIntensity’ was significantly better than strategy ‘FDuration’ in terms of heat-stress duration (P<0.05; reduction 45.1%) and heat-stress intensity (P<0.01; reduction 70.7%). Also, during the hottest day (Julian 176) it resulted in: (i) a lower daily average inside temperature (28.5 vs. 31.8 °C; reduction 10.4%), (ii) a smaller daily inside dry-bulb temperature variation (8.7 vs. 10.3 °C; reduction 15.5%) and (iii) a higher reduction of peak outside temperature (36.8 °C at 14:00 h), namely 2.9 vs. 0.2 °C, respectively. For both strategies and heat-stress indices July was the most stressful month and May the mildest. In areas characterised by high outside temperatures and scarce water resources strategy ‘FIntensity’ should be implemented with caution as larger water quantities, in comparison to strategy ‘FDuration’, need to evaporate.