222 Effect of electronically controlled floor cooling pad on thermoregulatory performance of Duroc boars during the summer heat stress period

The objective of the study was to evaluate the effects of using electronically controlled floor cooling pad (ECP) to reduce physiological heat stress response during the summer season in a boar stud in Scottsville, Kentucky. Boars (n = 60; 526 ± 188 d of age) were placed in two rows of pens (2.06 x 0.66 m) of a 350 head tunnel ventilated boar barn and were randomly assigned to either CONTROL (n = 30; no ECP) or ECP treatments (n = 30). The ECP had 4.25 L cold water flushed through a group of 5 pads connected to each other, when temperature sensors reached 27°C or every 4 min for sensors placed on 5th pad and 24°C or every 4 min for sensors placed on 1st pad. Boars experienced a natural summer heat stress environment (daily temperature, humidity and dew point: mean = 24.03°C, 87.9%, 21.7°C, hourly mean high = 28.9°C, 83.4%, 25.8°C) for a period of 30 d from July 15, 2023 to August 14, 2023 wherein the cooling pad remained on and were flushing based on the set points mentioned above. Daily physiological measurements included respiration rate (RR), rectal temp (RT) and feed refusal (FR) collected during the hottest part of the day (1300 to1600 h) via counting chest or belly rises, using rectal thermometer and visual estimation, respectively. A mixed model in SAS (v.9.4) including the fixed effects of ECP, week, day, boar ID and their interactions with day in the week included as a random effect was used for the statistical analysis. Both RR and RT were decreased by ECP (P < 0.001), week (P = 0.027 and P = 0.005, respectively) and treatment by week interactions (P < 0.001). The overall RR and RT for boars on ECP (Mean = 15.2 breaths/minute, 38°C) were more stable compared with Control (Mean = 43.4 breaths/minute, 38.4°C). Increased RR (Mean = 55.7 breaths/min; daily high = 164 breaths/minute) and RT (Mean = 38.7°C; daily high = 40°C) were noted in wk 30 and 33 for CONTROL group while ECP group remained stable. The wk 30 and 33 RR and RT are caused by increased environmental temperatures and humidity (hourly mean high: temperature = 28.9°C, humidity = 84.9%, dewpoint = 21°C). FR increased as barn temperatures increased and treatment by week interactions were significant (P < 0.001), with a tendency for ECP to be overall less than CONTROL at P = 0.064. CONTROL boars had greater FR than ECP boars for wk 31 (P < 0.001), 32 (P = 0.001) and tendency for wk 33 (P = 0.098). These results indicate that the ECP effectively reduced the RR, RT and FR across the weeks with