Assessment of an Alternative Technique for Measuring Body Temperature in Pigs

Body temperature (BT) is one of the main vital signs that is used to evaluate the health status of pigs. The most commonly practiced method for measuring BT in pigs is rectal temperature (RT), since many have assumed that rectal temperature is the best indicator of core BT (CBT). Obtaining rectal temperature can be stressful for animals, may generate inaccurate results due to the presence of feces in the rectum, and has the risk of spreading disease. Infrared imaging (IR) of the eye may be used as safer and less stressful alternative to RT. However, to our knowledge the relationship between eye temperature and CBT has not yet been established. Therefore, the objective of the current study was to evaluate the feasibility of using IR imaging as an alternative to rectal temperature for monitoring CBT in pigs. A total of twenty-three gilts (initial BW 30.5 ±5.62 kg) were housed in metabolism crates in an environmentally controlled facility, and slightly feed restricted to ensure equal DM intake, and to minimize the variability in temperature readings caused by the heat of digestion. After 4 d of adaptation, febrile response was induced by intramuscular injection of E. coli lipopolysaccharide (LPS; 25µg/kg BW). BT of each pig was recorded at time 0, 2, 4, 6, 8, 10, and 24 hours post-LPS challenge, using the following three methods: (I) RT, (II) IR imaging of the eye using an IR thermography camera, (III) BCT using a CorTemp disposable sensor and a miniature digital recorder. Statistical analysis was carried out using MIXED and CORR Procedures in a Completely Randomized Design using SAS. Reg Procedures in SAS were used to estimate regression parameters. LPS increased the eye temperature, BCT, and RT by 0.92, 1.32, and 1.48 °C, respectively (P< 0.01). Eye temperature, RT, and BCT were highly correlated during the course of the study (ρ ≥ 0.96; P<0.01). Estimated regression parameters (α and β) for predicting BCT using eye temperature were -28.2 ±8.70 and 1.76 ±0.221, and for RT were -24.5 ±7.69 and 1.65 ±0.196 (r² _≥ 0.96; 95 % confidence interval). Collectively, these results indicated a strong relationship between eye temperature and BCT in pigs. Therefore, IR imaging can be used as a precise, non-contact alternative to rectal temperature measurements for monitoring CBT in swine, and possibly other species.