Field Evaluation of Infrared Thermography as a Screening Tool for Calf Health

Abstract

Early detection of disease in dairy calves is essential for maintaining animal welfare, reducing mortality and economic losses, minimizing disease transmission, and enabling timely veterinary intervention. However, routine clinical examination of individual calves is labour-intensive, time-consuming, and often impractical under herd conditions. Infrared thermography (IRT) offers a rapid, non-invasive, contact-free approach for monitoring physiological changes through detection of alterations in surface temperature associated with inflammation, peripheral blood flow, and tissue metabolism. The present study was undertaken to evaluate the potential of IRT as a practical herd-level screening tool for identifying calves exhibiting abnormal thermal profiles under field conditions and to assess the relationship between thermographic measurements and conventional physiological and haematological indicators of health. The study was conducted at the Livestock Research Centre, ICAR–National Dairy Research Institute, Karnal, Haryana, India. A total of 100 mixed-breed dairy calves, comprising both male and female calves aged between 5 days and 3 months, were initially screened using a Fluke TiX580 infrared thermal camera. Thermal images were acquired under standardized environmental conditions without physical restraint of the animals. Thermographic assessment included selected thermal windows comprising the body surface, forehead, muzzle, and left and right ocular regions. A fixed imaging distance of 1 m was maintained during image acquisition, and the same operator conducted the imaging throughout the study to minimize operator-related variation. The camera emissivity was maintained at 0.95, and thermal images were analysed using SmartView Classic 4.4 software. During the initial herd-level screening, calves exhibiting localized or generalized elevations in surface temperature or other abnormal thermal patterns relative to the remaining herd were identified as thermally suspect and selected for further veterinary evaluation. These calves subsequently underwent detailed clinical examination by a registered veterinary officer. Physiological parameters, including rectal temperature (RT), respiratory rate (RR), and heart rate (HR), were recorded using standard veterinary procedures. Respiratory rate was determined by counting flank movements for one minute without disturbing the animals, whereas heart rate was recorded using a Polar H10 heart rate monitor. Rectal temperature was measured using a digital thermometer. Approximately 5 mL of blood was collected from the jugular vein into EDTA-containing vacutainers for complete blood count analysis using an automated veterinary haematology analyser. Based on comprehensive clinical examination and confirmatory veterinary assessment, 36 calves fulfilling the study criteria were classified into three groups: healthy calves (n = 12), calves affected with calf scour (n = 12), and calves affected with bovine respiratory disease (BRD; n = 12). Importantly, the final disease classification was based on conventional veterinary examination and diagnostic procedures, while IRT was used as an initial screening method to identify animals requiring further evaluation. The thermographic, physiological, and haematological data were subsequently analysed statistically. Data were assessed for normality using the Shapiro–Wilk test, and group differences were evaluated using one-way analysis of variance followed by Tukey’s multiple comparison test. Pearson’s correlation analysis was used to determine associations between thermographic variables and physiological and haematological parameters, with statistical significance considered at P < 0.05. The results demonstrated significant differences (P < 0.05) in thermographic temperatures of the eyes, forehead, muzzle, and body surface among healthy calves, calves affected with calf scour, and BRD calves. The highest thermographic temperatures were recorded in calves affected with BRD, followed by calves with calf scour and healthy calves. These findings indicate that disease-associated inflammatory and physiological alterations were reflected in peripheral thermal profiles and could be detected through infrared imaging. Furthermore, thermographic measurements showed strong positive correlations with rectal temperature, heart rate, total leukocyte count, and granulocyte count, whereas lymphocyte count exhibited significant negative correlations with the thermographic parameters. The observed associations between thermal measurements and conventional physiological and haematological indicators provide additional support for the biological relevance of the detected thermal alterations. The findings demonstrate that IRT has considerable potential as a rapid and non-invasive herd-level screening technology for identifying calves with abnormal thermal profiles under field conditions. Its ability to assess animals without physical contact or restraint makes it particularly advantageous for routine herd surveillance, where rapid identification of potentially diseased animals is important. However, IRT should not be considered a standalone diagnostic technique because thermographic changes may be influenced by environmental conditions and other physiological factors. Instead, it may serve as a first-line screening tool to flag animals requiring detailed clinical and laboratory evaluation. The practical significance of IRT was particularly evident in its ability to screen a relatively large number of calves rapidly and without direct animal handling. Unlike conventional temperature measurement and clinical examination, thermal imaging can be performed with minimal disturbance, thereby reducing handling-related stress and facilitating repeated observations. The simultaneous assessment of multiple anatomical thermal windows also provides a broader representation of the animal’s thermal status than a single physiological measurement. The distinct thermal patterns observed among healthy, calf scour, and BRD groups suggest that different disease conditions may produce characteristic changes in peripheral temperature distribution. Incorporating such information into herd monitoring systems may therefore improve the efficiency of health surveillance and assist veterinarians in prioritizing calves for detailed examination and intervention. Overall, the present study highlights the potential application of infrared thermography within precision livestock farming for routine calf health surveillance. Integration of IRT with conventional physiological and haematological assessment may facilitate earlier identification of calves at risk of disease, enable timely veterinary intervention, improve herd health management, and potentially reduce disease-associated economic losses. Further studies involving larger populations, longitudinal monitoring, standardized environmental conditions, and automated thermal-image analysis are warranted to establish robust diagnostic thresholds and improve the field applicability of IRT for early calf disease detection. Keywords: Infrared Thermography; Dairy Calves; Herd-Level Screening; Calf Scour; Bovine Respiratory Disease; Thermographic Temperature; Haematology; Precision Livestock Farming.