Effects of Floor Cooling on Late Lactation Sows Under Acute Heat Stress

The objective was to evaluate the effects of floor cooling on late lactation sows under severe summer heat stress. Ten multiparous sows were provided with a cooling pad built with an aluminum plate surface, high-density polyethylene base and copper pipes. Treatments were randomly allotted to sows to receive a constant cool water flow of 0.00 (CONTROL, n = 4), 0.25 (LOW, n = 2), 0.55 (MEDIUM, n = 2) or 0.85 (HIGH, n = 2) l/min for 100 min. The cooling was initiated 1 h after the room reached 35ºC. Respiration rates (RR), vaginal temperature (VT) and skin temperature (ST, 15 cm posterior to the ear) were recorded before the trial, prior to cooling, and 5 times (every 20 min) after the cooling phase started. Rectal temperature (RT) was recorded before the trial, prior to cooling and in the last 20 min of cooling. Water flow rates, inlet and outlet water temperatures were recorded 5 times (every 20 min) to calculate heat removal (watts) after the cooling initiation. The same procedure was repeated 8 times (2 times/day for 4 days). In each repetition treatments were switched randomly. Data were analyzed using the MIXED procedure in SAS. For the pre-trial and pre-cooling RR, VT, RT and ST measurements, the model included treatment as fixed effect and repetition as a random block. During the cooling phase, RR, VT and ST, and heat removal were analyzed using repeated measures with sow as a repeated random effect. The model included treatment, cooling time and their interactions as fixed effects. The mean room temperature and relative humidity during the trial were 35.1 ± 0.4ºC and 68.4 ± 3.2%, respectively. The treatments impacted RR, VT, ST and RT after 80 min of cooling, where the mean RR was 122, 76, 67 and 45 breaths/min for the CONTROL, LOW, MEDIUM and HIGH treatments, respectively (P < 0.001). After 80 min of cooling the mean VT, RT and ST were 40.1, 40.0 and 39.4ºC for the CONTROL; 39.5, 39.5 and 39.0ºC for the LOW; 39.4, 39.2 and 38.9ºC for the MEDIUM; and 39.2, 39.0 and 38.6ºC for the HIGH treatment, respectively (P < 0.001). Overall heat removal during the trial was 192.7, 320.7 and 364.8 watts for the LOW, MEDIUM and HIGH treatments, respectively (P < 0.001). Cooling pads with LOW, MEDIUM and HIGH water flow rates reduced RR, RT and VT in lactating sows.