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ARS Home » Midwest Area » West Lafayette, Indiana » Livestock Behavior Research » Research » Publications at this Location » Publication #321297

Title: Core body temperature does not cool down with skin surface temperature during recovery at room temperature after acute heat stress exposure


Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2016
Publication Date: 7/9/2016
Citation: Sapkota, A., Herr, A., Johnson, J., Lay Jr., D.C. 2016. Exposure to thermoneutral conditions following acute heat stress reduces skin temperature and increase core body temperature in pigs. Livestock Science. doi:10.1016/j.livsci.2016.07.010.

Interpretive Summary: Commercially raised pigs are subjected to, multiple environmental stressors throughout their lifetime. In particular, environmentally-induced heat stress can result in morbidity and mortality and the lack of functional sweat glands make pigs particularly susceptible to the effects of heat. Thermal conditions for pigs has been recommended ranging from 26 to 32°C for pre-nursery pigs to 10 to 25°C for finishing pigs. The stress of handling can also stimulate an increase in heat production by the pig resulting in an increase in heat stress susceptibility. A key indicator of stressed swine is thus an elevated temperature. The study objective was to be able to use infrared thermography as a non-invasive approach to accurately monitor the welfare of swine by comparing changes in skin surface temperature, core body temperature, behavior and heart rate during acute heat stress and subsequent recovery in thermoneutral conditions. Pigs were subjected to acute heat stress (39.3 ± 0.1°C) for 30 minutes followed by thermoneutrality (20.6 ± 0.1°C) for 30 minutes. Skin surface temperature, core body temperature, heart rate, and behavioral data were recorded throughout the entire experiment. At room temperature ear base skin surface temperature could be used to estimate the core body temperature without handling pigs. When pigs were moved from acute heat stress to thermal neutral conditions, skin surface temperature dropped drastically within 10 minutes while core body temperature remained increased at least for another 30 minutes. Exposure to acute heat stress resulted in increased activity and restlessness in pigs. However, heart rate was not affected by acute heat stress or by returning pigs back to thermal neutral temperature after acute heat stress exposure. The ability to non-invasively monitor core body temperature by using infra-red thermography of the skin temperature will allow researchers to accurately determine if pigs enter a state of heat exhaustion.

Technical Abstract: Identifying new methods of assessing livestock welfare is a growing area of research. Non-invasive methods of assessment such as infrared thermography are valuable for quick and accurate observations and could be utilized to monitor the thermal status of swine without direct contact. The objectives of this study were to determine correlations between skin surface temperature (SST) and core body temperature (CBT) and evaluate how heart rate and behaviors change during acute heat stress (AHS). In eight replications, 16, 98.2 ± 2.0 kg pigs (mixed sex) were subjected to AHS (39.3 ± 0.1°C) for 30 min followed by thermoneutrality (Recovery; 20.6 ± 0.1°C) for 30 min. The SST, CBT, heart rate, and behavioral data were recorded throughout the entire experiment. At baseline, ear base SST was greater (P < 0.01; 35.6 ± 0.3°C) than all other body parts. The SST at all locations increased with duration of AHS exposure for 30 min (P < 0.01). During Recovery, maximum CBT was greater (P < 0.01; 40.7 ± 0.1°C) compared to CBT during AHS (40.3 ± 0.1°C). Pigs spent more time standing during AHS (P = 0.007) and tended to lie more during Recovery (P = 0.1); however, heart rate was (average: 141 ± 2.3 beats per minute) not affected by treatment or duration. In summary, elevated SST during AHS is reduced during rapid exposure to TN; however, CBT is actually increased and this could lead to reduced activity and greater organ damage due to a reduced ability to dissipate body heat.