PSXII-24 Time course determination of the effects of rapid and gradual cooling after heat stress on body temperature and intestinal integrity in pigs

Abstract Rapid cooling after acute hyperthermia may cause a sustained increase in body temperature and intestinal damage in pigs given free access to feed. Therefore, the study objective was to evaluate the temporal effects of rapid and gradual cooling on body temperature response and intestinal integrity after acute hyperthermia in pigs when feed was withheld. In three repetitions, 54 mixed sex pigs (83.3 ± 6.7 kg) were exposed to either thermoneutral conditions for 6h (TN; n = 6 pigs/rep; 21.1 ± 2.0°C), or heat stress conditions (HS; 39.3 ± 1.6°C) for 3h, followed by a 3h recovery period of gradual cooling [HSGC; n = 6 pigs/rep; gradual decrease from HS to TN conditions] or rapid cooling (HSRC; n = 6 pigs/rep; rapid TN exposure and ice water dousing every 30 min for 1.5 h). Feed was withheld throughout the entire 6h period. Gastrointestinal (TG), rectal (TR) and skin (TS) temperatures were recorded every 15 min during the HS and recovery periods. Six pigs per repetition (n = 2/treatment) were euthanized and jejunal samples were collected for histology immediately after (d1), 2 d after, and 4 d after the recovery period. Data were analyzed using the PROC MIXED procedure in SAS 9.4. Rapid cooling reduced (P < 0.01) overall TR, TG, and TS (38.9°C, 40.1°C and 28.3°C, respectively) compared to gradual cooling (39.9°C, 40.9°C and 37.6°C, respectively). Villus height was similar on d1and d2 but increased (P = 0.01) on d4 by 24.6% in HSRC compared to HSGC pigs. Overall, crypt depth and the villus height-to-crypt ratio were greater (12.7% and 20.0%, respectively) in HSRC compared to HSGC pigs, but no day by treatment interaction was detected. In summary, rapid cooling after HS did not cause a sustained increase in body temperature and negatively impact intestinal integrity when feed was withheld.