Body temperature and its variations are essential indications of an animal's physiological health, stress level and well-being among other physiological measures. Stress generated by elevated body temperatures is a major constraint for farm animal output
At present, the correction factor (CF) as a substitute measures for accurate assessment of body temperature utilising infrared thermography as an alternative to rectal temperature has not yet been developed. Therefore, the objective of the present study was to select suitable sites based on the correlation between Trectal and body surface temperature at different body sites and develop CF to assess accurate body temperature using infrared thermal imaging camera (Tcamera) in pigs as an alternative to rectal temperature.
The experimental procedures were reviewed and approved by the Institutional Animal Ethics Committee (IAEC), ICAR-RC for NEH Region, Meghalaya. The animals were humanely treated during our study.
The experiment was conducted in Pig Breeding Farm, Division of Livestock Production of the Institute (2019-20). It is located at 24° 58’ N to 26° 07’ N latitudes and 89° 48’ E to 92° 51’ E longitudes with an altitude of 1010 meter above sea level.
An experiment was conducted separately for summer (July) and winter (December) in three different genetic groups viz, Hampshire, crossbred (Hampshire x Niang Megha) and Niang Megha (indigenous). In each season, a total of 90 pigs were taken for the study, with each genetic group consisting 30 numbers of apparently healthy adult pigs between 1-3 years. These pigs were reared under pen system of housing and provided with uniform managemental practices. Regular vaccination and deworming were carried out as per the standard procedures. Thermal images were taken twice daily between 9-11AM and 3-5PM for 6 days for each pig, With an environmental temperature range of 22 to 26°C in summer and 19 to 22°C in winter. All thermal images were captured using a thermal imager - Testo 875i (Testo India Pvt. Ltd. Pune, India). The emissivity of 0.95 was taken as standard emissivity of pig body surface in the study. The measurement of the body surface temperature was taken on five different anatomical sites viz, tip of the snout, eye, back temperature at lumbar region, base of the ear on the neck and inner thigh above the hock joint. Rectal temperature was measured in the rectum using Digital Thermometer (DT) with proper restraining of pigs to avoid stress. The thermographic images were analyzed using the software IRSoft Version 3.6 Testo (Testo India Pvt. Ltd. Pune, India). This software enabled to measure the temperature of specifically selected sites by simply defining them within each image and represented in
All statistical analysis was performed using SPSS statistical software (SPSS 14, 2006). The data obtained from the selected anatomical sites and Trectal of three different genetic groups were subjected to multivariate analysis to find out the significant level. The values were compared among the sites, genetic groups and seasons. For each site, the average Trectal and body surface temperature was calculated. The correlation between Trectal and body surface temperature of the selected sites in both summer and winter were calculated using correlation coefficient. Suitable sites were selected, based on the correlation between Trectal and body surface temperature of different sites of the body. Accordingly, constant correction factors (CF) was established to assess the rectal temperature in pigs using infrared thermography camera. Further, the CF was validated by conducting an experiment for 6 days with the same animals, breeds and seasons and predicted the rectal temperature on the identified sites.
The rectal temperature of domestic animal remains relatively constant but body surface temperature varies according to the environmental temperature. However, few anatomical sites maintain temperature close to the body temperature. This study aimed to identify suitable anatomical sites and develop CF for accurate body temperature assessment utilizing infrared thermal imaging camera as an alternative to rectal temperature. The baseline rectal temperatures in our study ranged from 36.19°C to 38.8°C for all the pigs evaluated. The average rectal temperature and body surface temperature from various anatomical sites of an experimental animals at different seasons are given in
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Rectal temperature |
37.8±0.12aA |
37.5±0.14aA |
37.7±0.12aA |
37.17±0.11aA |
37.19±0.13aA |
37.59±0.10aA |
Base of the ear |
33.75±0.11bB |
34.25±0.13bB |
34.9±0.24bB |
32.35±0.21bB |
32.94±0.13bB |
32.66±0.2bB |
Inner thigh |
32.75±0.23cB |
33.25±0.15cB |
32.3±0.22cB |
31.57±0.14cB |
32.10±0.31cB |
31.54±0.16cB |
Eye |
32.9±0.16dB |
33.85±0.11dB |
32.8±0.21dB |
32.24±0.31dB |
32.87±0.14dB |
32.68±0.21dB |
Snout |
26.5±0.05eC |
27.7±0.07eC |
27.9±0.02eC |
21.72±0.04fC |
22.04±0.06fC |
21.85±0.01fC |
Back |
27.4±0.07gC |
28.2±0.04gC |
28.8±0.08gC |
21.84±0.06hC |
22.11±0.03hC |
21.53±0.02hC |
Different superscript in rows and columns indicate the significant difference (p<0.01). Capital letter in superscripts has been used for column wise comparison and small letter for row wise comparison, N=number of pigs.
Some studies investigated the correlation between rectal temperature and body surface temperature measured by infrared thermography. As previously reported, thermal temperature of base of the ear, inner thigh and eye regions showed positive correlation with the rectal temperature in the present study (
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Rectal temperature |
37.8±0.12 |
37.5±0.14 |
37.7±0.12 |
37.17±0.11 |
37.19±0.13 |
37.59±0.10 |
Base of the ear |
0.84aA |
0.87aA |
0.84aA |
0.90aA |
0.91aA |
0.85aA |
Inner thigh |
0.67bB |
0.7bB |
0.74bB |
0.76bB |
0.72bB |
0.7bB |
Eye |
0.85cA |
0.84cA |
0.86cA |
0.87cA |
0.78cA |
0.83cA |
Snout |
0.41 |
0.51 |
0.42 |
0.4 |
0.5 |
0.4 |
Back |
0.36 |
0.38 |
0.4 |
0.34 |
0.45 |
0.47 |
Different superscript in rows and columns indicate the significant difference (p˂ 0.01). Capital letters in superscripts used for column wise comparison and small letter for row wise comparison. |
In our study, two anatomical sites were selected (base of the ear and eye) for assessment of the rectal temperature based on the close relation with Trectal in pigs. Prediction of body temperature using thermal image camera has been earlier reported
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Trectal |
37.8 |
37.5 |
37.7 |
37.17 |
37.19 |
37.59 |
37.49 |
- |
Tear |
33.75 |
34.25 |
34.9 |
32.35 |
32.94 |
32.66 |
33.48 |
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Teye |
32.9 |
33.85 |
32.8 |
32.24 |
32.87 |
32.68 |
32.89 |
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*Correction Factor (CF)=Average Trectal
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Hampshire N=30 |
37.8±0.02 |
37.25±0.05 |
37.2±0.07 |
37.2±0.01 |
36.45±0.1 |
36.3±0.08 |
Crossbred N=30 |
37.3±0.03 |
37.85±0.02 |
38.2±0.07 |
37.5±0.02 |
36.9±0.06 |
37.1±0.05 |
Indigenous N=30 |
37.5±0.05 |
38.25±0.07 |
37±0.02 |
37.6±0.04 |
36.59±0.08 |
35±0.06 |
Average |
37.53±0.15 |
37.78±0.29 |
37.47±0.37 |
37.43±0.12 |
36.65±0.13 |
36.13±0.16 |
Tear = base of the ear temperature, DT=digital thermometer, Teye =eye temperature, CF= correction factor, N = number of pigs, CF for Tear= 4 and CF for Teye = 4.6.
The overall mean differential value of Tear was approximately within (±) 0.8°C of the corresponding rectal temperature. However, the Teye of Tcamera tend to be lower than rectal temperature by 0.06°C in summer and approximately 1.3°C in winter. Thus, base of the ear and eye temperature measurements were considerably reliable indicators of rectal temperature with thermography technique using the developed CF in the present study. Indeed, the wide variation between the season can be due to the external environmental factors as it was mention earlier by Church et al
In conclusion, we have confirmed from our study that infrared thermal imaging of body surface (base of the ear and eye) with correction factors (base of the ear = 4 and eye = 4.6) could be used as an alternative method to assess Trectal accurately. Using these correction factors as an alternative methods, abnormal health status of the pigs can be recorded rapidly, avoiding the stress of restraining pigs during conventional method of measuring body temperature. However, further validation is required in large number of pigs at different season for enhancing accuracy.
The authors thankfully acknowledge to National Innovation on Climate Resilient Agriculture (NICRA) 217 project, Indian Council of Agricultural Research (ICAR) for providing funding and facilities to conduct the research.