Evaluation of Floor Cooling on Lactating Sows Under Moderate Heat Stress within a Day and Relationships of Measures of Heat Stress to Estimated Heat Removal Rates

The objective was to evaluate relationships between changes in physiological measurements and estimated heat removal (HR) of lactating sows on cooling pads. Moderate heat stress rooms were targeted to achieve 32ºC from 0800-1600 h and 27ºC for the rest of the 24-hour day. Mild heat stress rooms were targeted to achieve 27ºC and 22ºC for the same periods, respectively. Each sow was provided a cooling pad with either a constant cool water flow of 0.00 (CONTROL, n = 9), 0.25 (LOW, n = 12), or 0.50 (HIGH, n = 10) L/min. Water inlet and outlet temperatures and flow rates were recorded to estimate HR. For the overall trial, respiration rates (RR), rectal temperature (RT), and skin temperature (ST) were recorded every day (0700 and 1500 h) from the second day in the farrowing room to weaning at 17 to 20 d. Regression analyses were used to evaluate changes in RT and RR relative to estimated HR. The difference in RT and RR for sows on the LOW and HIGH pads relative to the CONTROL sows was calculated for each AM and PM measurement. The change in RR per watt of HR were similar for the LOW and HIGH pads (b = -0.626 and -0.586) with lower R² values for LOW than HIGH pads (0.424 versus 0.698). The change in RT per watt of HR were greater (P < 0.05) for the LOW than HIGH pads (b = -0.0091 versus -0.0066) and R² values were less for LOW than HIGH pads (0.188 versus 0.399). An intensive 2-d study was performed on sows in the moderate heat stress room on the CONTROL (n = 3) and HIGH (n = 3) treatments (14.2 ± 1.8 d of lactation). Respiration rate, and RT were recorded at 0600, 0700, 0730, 0800, 0830, 1100, 1400, 1500, 1530, 1600, 1630, and 1900 h. The cooling pad treatment affected RR (52 and 30 breaths/min, CONTROL versus HIGH, P < 0.05). The RR of CONTROL sows increased as the room temperature increased (P < 0.05) after 0830 h and remained higher until 1600 h. The RR of HIGH sows did not change between 0830 and 1700 h. The HR rates were affected (P < 0.003) by measurement time. The greatest HR (220-230 watts) were from 1530-1630 h. The effect of cooling pads to reduce RR and RT increased as the room temperature and HR increased.