Time course determination of the effects of rapid and gradual cooling after acute hyperthermia on body temperature and intestinal integrity in pigs

Authors: KPODO, KOUASSI - Purdue University; DUTTLINGER, ALAN - Purdue University; RADCLIFFE, JOHN - Purdue University; Johnson, Jay

Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2019
Publication Date: 12/13/2019
Citation: Kpodo, K.R., Duttlinger, A.W., Radcliffe, J.S., Johnson, J.S. 2019. Time course determination of the effects of rapid and gradual cooling after acute hyperthermia on body temperature and intestinal integrity in pigs. Journal of Thermal Biology. https://doi.org/10.1016/j.jtherbio.2019.102481.
DOI: https://doi.org/10.1016/j.jtherbio.2019.102481

Interpretive Summary: Acute hyperthermia negatively affects animal health and well-being, resulting in economic losses due to increased health care costs and mortality. In animal agriculture, swine are more susceptible to acute hyperthermia in tropical regions and during warm summer months in temperate climates. To alleviate the negative impacts of heat stress in pigs, different cooling methods such as cooling pads, ventilation, and evaporative cooling are used; however, these methods may not be adequate during acute hyperthermia. Previous studies determined that rapid cooling (ice water immersion) increased intestinal damage and reduced the ability of pigs to dissipate body heat following acute hyperthermia. Therefore, the study objective was to evaluate the temporal effects of rapid cooling on body temperature, intestinal morphology and integrity, and inflammatory response after acute hyperthermia in pigs. We hypothesized that rapid cooling after acute hyperthermia would prolong the body temperature increase, thereby increasing hyperthermia-induced intestinal damage and inflammatory responses with long-lasting effects post recovery. Contrary to our hypothesis, it was determined that rapid cooling after acute hyperthermia was effective in reducing intestinal damage and returning the body temperature to normal after acute hyperthermia in pigs. This response was partially attributed to the fact that pigs were not able to consume feed during the acute hyperthermia and recovery procedures. It is now hypothesized that feed withdrawal can assist pigs in returning to a normal body temperature more rapidly after acute hyperthermia and future studies will attempt to determine whether this hypothesis is correct.

Technical Abstract: Rapid cooling after acute hyperthermia may cause a sustained increase in body temperature and exacerabate intestinal damage in pigs. 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. In three repetitions, 54 pigs [83.3 ± 6.7 kg initial body weight (BW)] balanced by sex were exposed to 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/repetition; gradual decrease from HS to TN conditions] or rapid cooling (HSRC; n = 6 pigs/repetition; rapid TN exposure and cold water dousing every 30 min for 1.5h). Feed was withheld throughout the entire 6h period, but water was provided ad libitum. Gastrointestinal (TGI) and rectal (TR) temperatures were recorded every 15 min during the HS and recovery periods. Six pigs per repetition (n = 2/treatment) were euthanized and jejunal and ileal samples were collected for histology immediately after (d0), 2d after, and 4d after the recovery period. Data were analyzed using the PROC MIXED procedure in SAS 9.4. Overall, rapid cooling reduced TR and TGI (P < 0.01; 0.95°C and 0.74°C, respectively) compared to gradual cooling. Jejunal villus height was reduced overall (P = 0.02; 14.01%) in HSGC compared to HSRC and TN pigs. Jejunal villus height-to-crypt depth ratio was reduced overall (P = 0.05; 16.76%) in HSGC compared to TN pigs. Ileal villus height was reduced overall (P < 0.01; 16.95%) in HSGC compared to HSRC and TN pigs. No other intestinal morphology differences were detected. In summary, HSRC did not cause a sustained increase in body temperature and did not negatively impact biomarkers of intestinal integrity in pigs.