PSI-A-13 Changes in Daily Patterns of Physiological Measures of Heat Stress on Sows in Cool Room and in Heated Room with and without a Cooling Pad

Abstract Impacts of heat stress (HS) on lactating sows during the summer causes challenges in production. The study objective evaluated the daily patterns of common HS measures on late lactation sows. Sows in a HS environment, on and off electronic cooling pads (ECP), were compared with sows in a cool room (CR). From a sample of six sows, three sows were assigned to a HS environment, (31°C daytime for 6 h and 26°C nighttime for 5 h) with an ECP (n = 1) or without an ECP (nECP, n = 2). Three sows were placed in a CR (n = 3) with set temperature of 20°C. The ECP automatically flushed 2.0 L of cool water (18 to 19°C) when one of the three temperature sensors reached 26°C. Flushing occurred for 30 s replacing 1.73L of water in the ECP. All sows were in farrowing crates and provided ad libitum access to feed and water. Internal Temperature (TI) was measured in 10-minute intervals using vaginal implants. Skin temperature (TS) was measured hourly, using an infrared gun 10 cm behind the ear. Respiration rate (RR) was observed in 30-minute intervals from 0600 to 2200 h over 2 days. Mixed model periodic regressions were performed in R 4.2.2 using REML lme4, fitted to the RR, TS, and TI data. Significant treatment and treatment by periodic regression variables (P < 0.05) indicated the need for separate equations for each treatment. The final model for TI included the random effect of sow, effect of room, and single, double, and triple sine/cosine phase variables for each room. For TI, there were also significant (P < 0.001) interactions of the single-phase sine/cosine variables with the ECP treatment in the HS environment. The final model for TS included the random effect of sow, ECP treatment, single, double, and triple sine/cosine and their interactions with room, and the interaction of the single phase with ECP treatment in the HS environment. The final model for RR included the effects of room and ECP within the HS environment (P < 0.001), the single-phase sine/cosine variables, and their interactions of ECP within the HS environment and CR. Daily increases in RR and TI were much greater for sows in the HS environment compared with the CR, or the sow on the ECP. The RR for the ECP sow increased from 18 to 24 bpm from 6000 h to mid-afternoon (1500 to 1700 h), versus 65 to 108 bpm for the nECP sows. Overall, the ECP reduced TI on average by 0.39°C with the greatest impact of 0.8 to 0.9°C from 1500 to 1900 h. As in previous experiments, the sow on the ECP had greate