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Applications of infrared thermography as a non-invasive technique early indicator of fever in the lambs
Blasco Castello, J.L., Gutierrez...
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Objectives
Ovine Respiratory Complex (ORC) is one of the main causes of morbidity and mortality in sheep feedlots with high prevalence and economic repercussions (González, 2018). Early ORC diagnosis is essential to minimize the effects of the disease, related with both the productive results and welfare of the animals.
Body temperature is an objective clinical data, although its increase is not always associated with disease, as can be also a response to the high environmental temperature or exercise. However, when it is associated with other more specific clinical signs, it is very useful for early diagnosis. Indeed, studies monitoring temperature using ruminal boluses in cattle, demonstrate how the thermal increase occurs 12-136 h before the caregiver detected other more specific clinical signs of pneumonia (Timsit et al., 2011).
On the other hand, thermography is a technology with increasing use in different fields of the veterinary medicine. Thermographic cameras detect infrared radiation emitted by the surface of that body, converting it into an electrical signal that is transformed into a color image. Indeed, Schaefer y col. (2007) already demonstrate it is useful to identify early disease in cattle. However, environmental temperature at the time of thermal image can affect rectal temperature (Church et al., 2014).
Then, the purpose of this study was to evaluate the use of an infrared thermographic camera taking into account environment temperature for the detection of animals with hyperthermia in an intensive lamb herd.
Material and methods
This study was carried out in a lamb fattening farm located in Córdoba (Spain). Infrared temperatures were measured in a total of 2,842 multiple source commingled Merino lambs and its crosses, 60 to 120 days old, and 18 to 30 Kg live body weight. Following previous Schaefer et al. (2007 and 2012) studies in cattle, we performed an orbital eye measurement, as in other anatomical parts the presence of hair or wool can interfere with results.
The measurements were made after the passage of the lambs through the handling or sorting sleeve and in the lazarette measuring in duplicate both rectal temperature with a conventional thermometer and eye thermal image with an infrared thermometer.
For infrared thermography the camera Testo model 870 was used, with a resolution of 160 x 120 pixels (with the possibility of increasing to 320 x 240 pixels), thermal sensitivity <100 mK, 34º lens with fixed focus and integrated and calibrated digital camera. The image processing software was the IRSoft Software, version 4.5. While the thermometer used was the Kruuse clinical thermometer, model Veterinär-thermometer SC 12, also calibrated, with automatic stop system by sound signal and with a measurement accuracy of 0.1ºC.
At measurement time, the following data were additionally recorded: date and time, farm identification, barn, pen, etc. In addition, the inside and outside barn temperature was noted. Subsequently, we calculate a new parameter: the difference between rectal and ocular temperature (DROT).
The data were analyzed using Anova one-way for the comparison of means, as well as the correlation between the variables and the multiple linear regression using the statistical program IBM SPSS Statistics, version 25.
Results and discussion
We evaluate the effect of barn temperature on the ocular and rectal temperature. On the other hand, we evaluate its effect on different rectal temperature strata.
The correlations between the different variables were significant. Indeed, the combined use of variables, eye temperature and barn temperature, allowed us to establish a formula predicting the rectal temperature with an excellent correlation (R2 = 0.9996).
Rectal tª = 1.099 * ocular tª - 0.038 * tª nav
Conclusions
The rectal temperature of lambs under intensive conditions is an objective clinical parameter very useful for ORC early diagnosis. Infrared thermography is a fast, automatic and non-invasive technique helpful for early identification of sick animals. And considering the barn temperature at lecture time improves its correlation with rectal temperature.
Keywords: Fever, thermography, lambs, environmental Tª, ORC.
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