Research room design using artificial heat sources to implement heat stress studies of pigs

Heat stress continues to be an important challenge for the swine industry, largely due to continued genetic improvements resulting in leaner animals with higher metabolic heat production coupled with climatic changes trending towards warmer temperatures. In northern climates, there are two likely scenarios that would allow the study of heat stress in commercial barns. The use of natural summer heat to stress the pigs while mechanically cooling non-stressed pigs or using cool winter temperatures to create a thermoneutral environment for non-stressed pigs while using supplemental heat to induce heat-stress. Our experiment was designed to demonstrate the latter approach and was completed in a commerciallike growing-finishing pig barn mimicking historical hot weather conditions found in Southern Minnesota. The winter experiment maintained one room in the pig's thermoneutral zone (TN) by controlling ventilation with ambient inlet air while another room exposed pigs to heat stress (HS) temperatures with the use of natural gas-fired heaters and minimum ventilation. Pigs (n = 432; 9 pigs/pen; 24 pens/room) with average starting weight of 25 kg were placed in a growing-finishing pig barn at a research farm located at Morris, MN. Pigs were weighed monthly throughout the experiment and average daily feed intake (ADFI) was calculated. Average daytime and nighttime temperatures for the HS room were 29°C and 22°C, respectively, and 17°C and 15°C, respectively, for the TN room. Heat stress was evident in the HS pigs as indicated by greater respiration rates observed on the third (P < 0.05; SE = 7.78; 83 vs 28 breaths/minute, respectively) and fourth observation dates (P < 0.05; SE = 7.78; 128 vs 29 breaths/minute, respectively) when compared to TN housed pigs. Average daily feed intake was also reduced for the HS pigs (P < 0.05; SE = 0.04) at the end of periods 2 (2.77 vs. 3.00 kg) and 3 (2.85 vs. 3.27 kg) compared to TN housed pigs. Average daily gain (ADG) did not differ during the first two observation periods and only tended to differ (P < 0.10, SE = 0.02) at the end of the experiment (0.83 vs. 0.87 kg) with the TN pigs gaining slightly more than the HS pigs. However, gain:feed ratio (G:F) was greater (P < 0.05; SE = 0.005) for the HS pigs during period 2 (0.34 vs. 0.32) and period 3 (0.29 vs 0.27) than for the TN pigs. Average CO₂ concentrations were below 5,000 ppm (2,800 and 3,400 ppm for HS and TN rooms, respectively) and NH₃ concentrations were similar (9 and 14 ppm for the HS and TN rooms, respectively). The findings of this experiment demonstrate that it is technically possible to conduct a heat stress experiment during the winter, utilizing existing heat sources to impose heat stress on pigs.