Is infrared thermography a reliable early detector of disease in cattle?

J.S. Churcha, P.R. Hegadorena, M.J. Paetkaua, C.C. Millerb, G. Regev-Shoshanib, A.L. Schaeferc, K.S. Schwartzkopf-Gensweind (2013), Influence of environmental factors on infrared eye temperature measurements in cattle, Research in Veterinary Science vol 96, issue 1, 220-226.

Animal welfare issues in the livestock industry are gaining increasing attention, and there is growing public support for the implementation of higher animal welfare standards in this industry. The ability to measure eye temperatures in cattle in a non-invasive manner, to detect fear- and pain-related responses, can be a powerful tool that enables us to act in the interest of the animal where otherwise this might not have been possible. It could assist in detecting disease in cattle in its early stages, thereby reducing animal suffering and costs. Additionally, it can be used as a tool for increasing consumer awareness and demand for higher animal welfare standards. Infrared thermography (IRT) has been used to measure eye temperature in cattle, but environmental factors that could influence these measurements, other than relative humidity and ambient air temperature, were never considered. This study therefore examined the accuracy of measuring eye temperature by using IRT when adjusted for wind speed, camera settings, distance to camera, and solar loading. The research team concluded that environmental factors do influence eye temperature and therefore need to be managed.

The researchers carried out three experiments; two field studies and one laboratory experiment. The first field study examined 73 Angus cross steers to establish the relationship between the animals’ rectal and measured IRT eye temperature. All animals were measured via both methods, within a 3-hour period. To minimise the influence of environmental factors, the test was carried out in a barn, where a portable weather meter was used to keep track of wind. For the second field study, 79 Holstein dairy cows were used to examine the effects of solar loading on IRT measurements. They were measured twice within a 30-minute time frame, first with exposure to direct sunlight, then in the shade. The cows were measured as they approached the feed bunks voluntarily. In addition, 52 dairy cows were used to measure the effect of wind speed. They were exposed to different wind speeds while their IRT eye measurements were taken from different distances. The researchers also performed a laboratory experiment to allow for more precise measurements, and used a ‘surrogate eye’ to study the effects of the environmental factors discussed.

Environmental factors need to be managed

The results indicate that both solar loading and wind speed significantly affect IRT eye temperature measurements. To a lesser extent, distance to the animal also influenced the accuracy of the measurements. Direct sunlight was found to increase IRT temperature. In addition, solar loading seemed to be largely dependent on the animals’ coat colour and strongly affected the measured IRT temperature. An increase in wind speed furthermore led to a decrease in IRT temperature. The laboratory experiment confirmed these findings. The laboratory study also provides us with information about the effects of distance; the IRT measurements decreased as the distance slowly went up from 0.5 to 3 meters. While the camera’s humidity settings did not seem to have a significant influence, the camera emissivity (effectiveness in emitting energy as thermal radiation) settings did; a change of 0.05 was followed by an increase in IRT eye temperature of 0.5°C. Finally, the team found that there were much larger variations in IRT temperature than in rectal temperatures measured. This confirms the importance of managing environmental factors when measuring temperatures in cattle with this technology.

Concluding, the research highlights the need for consistency and precision in IRT eye measurements. Future measurements should take environmental factors such as wind speed and solar loading into account, to avoid unusual variations in temperature (and early symptoms of diseases like bovine respiratory disease complex) going undetected.

World Animal Protection’s view

This study gives helpful insight into the environmental factors that need to be considered when using IRT for measuring eye temperatures in cattle. This is important to ensure the usefulness of these measurements. This information is valuable not only from an economic perspective, but most importantly can be used to increase the welfare levels of the animals involved.