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• An artificial heating protocol was validated by climate and animal parameters. • Weight of pigs had no effect on physiological parameters during a higher heat load. • The effect of reduced stocking density on heat stress in pigs was investigated. • A lower stocking density decreased the rise in rectal temperature during heat load. • A lower stocking density tended to result in a better daily gain across the trial. As climate change intensifies, heat stress mitigation for pigs becomes more important. Trials involving induced heat waves are useful to test several measures (e.g. reduced stocking density) at a faster rate, but only when accurately evaluated and validated. In the present study, we investigated the suitability of an artificial heating protocol at different pig weights (experiment 1). The impact of different stocking densities on fattening pigs during an artificial heat wave (experiment 2) was also investigated. Experiment 1: Forty 20-week-old pigs weighing 96.5 ± 7.3 kg (W 100) and forty 17-week-old pigs weighing 72.7 ± 9.9 kg (W 70) were housed in two compartments. An artificial heat wave (heat load) was induced for 3 days. During 3-day periods before, during and after the heat load, physiological parameters (respiration rate (RR), rectal temperature (T rectal), skin temperature (T skin) and behavior) were measured and average daily feed intake was observed. Ambient temperature, relative humidity and temperature-humidity index (THI) were monitored. Experiment 2: A total of 150 fattening pigs were randomly divided into three treatment groups: SD 1.3 (1.3 m2/pig), SD 1.0 (1.0 m2/pig) and SD 0.8 (0.8 m2/pig). All pens had a total pen surface of 4.88 m2, corresponding with 4, 5 and 6 fattening pigs in the SD 1.3 , SD 1.0 and SD 0.8 groups, respectively. The heat load was induced for 7 days on week 21. Respiration rate and T rectal were observed as in experiment 1. Average daily gain and average daily feed intake were also noted. During the heat load, THI reached ≥ 75 (78.4 (experiment 1) and 78.6 (experiment 2)), even when relative humidity decreased to ± 45%. Every physiological parameter showed significant increases during the heat load. The prolonged heating protocol in experiment 2 also provoked significant decreases in average daily feed intake (15%) and average daily gain (19%) for all groups. Weight within the studied range of 70–100 kg did not have a significant impact on any of the parameters. However, T skin was affected by both weight and heat load (P < 0.05), where T skin from W 100 was always lower in comparison to W 70. In addition, we found that 0.8 m2/pig doubled the increase of T rectal during the heat load, namely SD 0.8 (0.22 °C) compared to SD 1.0 (0.12 °C) (P = 0.033) and SD 1.3 (0.13 °C) (P = 0.053). This suggests that pigs housed at higher densities are less able to regulate their internal heat production. However, RR and performances were not significantly affected by heat load in this experimental set-up. A stocking density of 1.0 m2/animal may be sufficient to mitigate some negative effects of heat stress. [ABSTRACT FROM AUTHOR]