Do Environmental and Animal Factors Distort Infrared Imaging in Cattle?
Infrared radiation is emitted from all objects, and when measured can be used to determine surface temperature. Technology to measure infrared radiation was first used in 1950's for military use and has gradually evolved and has gained use in livestock sector. Some of these applications include early detection of inflammatory diseases, animal welfare, body condition score and feed efficiency. Despite all these possibilities, the use infrared technology is still limited for commercial operations because of the lack of standardized operation procedures for adequately performing infrared assessments across different scenarios.
Animal factors such as physical activity, feed intake prior to imaging, and individual response to drugs, could mask the underlying biological target to be assessed due to uncontrolled changes on the patterns of emitted radiation. Environmental factors include dirt, as well as weather factors such as direct sunlight and drafts, would also have the potential to skew infrared analysis due to interferences on the radiation emitted by the animals' body surface.
In addition, the choice of the infrared camera based on the different technological options (with different image resolution, cost, sensitivity and array of applications) should be taken into account. As well, the lack of consistency between judges analyzing the same thermographs could also interfere in the infrared imaging analysis.
The objectives of this study included evaluating animal factors' (exercise, drug effects and heat increment of feeding) and environmental factors' (sunlight, forced wind, and debris on animals' surface) effects on the infrared assessment, and to compare different types of infrared cameras and the repeatability of such assessments between judges.
What We Did
The study was divided into different trials: a repeatability trial, a camera and judge comparison trial, an exercise trial, a drug trial, a forced wind trial, a debris trial, a sunlight exposure trial, and a heat increment of feeding trial. All the trials were conducted at Elora Beef Research Center (University of Guelph) and consisted of baseline photos taken before and after every trial to compare temperature readings, and were taken while the animals were maintained in a head chamber calorimeter to assess metabolic rate, with the exception of the repeatability trial.
The repeatability trial was conducted using 127 weaned calves restrained in a squeeze chute while photos of their head were taken twice, consecutively with the FLIR SC2000 camera (Figure 1). The calves were again imaged three days later. Two groups of calves were assessed in two different weeks and body weight was measured on both occasions. The camera and judge comparison trial was conducted using different infrared cameras (FLIR i40, T250 and SC2000). Pictures of different body locations of a yearling beef heifer were taken from seven different distances (1.0m, 1.5m, 3.5m, 5.5m, 9.5m, 11.5m and 15.5m) with the three cameras. The same images were also analyzed by two judges to verify the repeatability of the interpretation across different judges.
Figure 1. Infrared imaging assessment (head imaging) of a heifer restrained in a squeeze chute.
The exercise trial used two yearling beef heifers. It consisted of 15 minutes of exercise (running) and three post-exercise photos were taken with the T250 camera every 20 minutes. The drug trial involved xylazine (sedative) and atipamezole (anti-sedative), with xylazine administered first, followed by a dose of atipamezole. Two sets of photos were taken every 10 min after the xylazine injection and two more were taken after atipamezole. The forced wind trial used the SC2000 camera; the fan was turned on (wind speed of 17 km/h) and blew on the right side of the animal. Photos were taken every 10 min for five rounds. The fan was then turned off and photos were taken every 10 min for 4 rounds (Figure 2). The debris trial consisted of two types of debris: manure and shavings. Pictures were taken before and after spreading manure on the caudal areas of all four legs, from hock to the bottom of the hoof. Similarly, shavings were placed on top of the animal's back, while images were taken before brushing off the shavings and after.
Figure 2. With the help of the infrared camera, it is possible to determine the surface temperature of the cattle, which might be influenced by several factors. For instance, during the forced wind trial, the start temperatures within the large squares (fan off; image A) were noticeably greater (35.9°C), than after exposure to the wind (33.5°C) (fan on; image B).
What We Found
- Distance had a strong influence on the temperature measured at given location. For instance, at 1m and 15m from the animal's eye the readings were 35°C and 32°C respectively.
- In addition, the models of infrared cameras evaluated gave substantial differences in thermographs taken on same location and time. For example, the T250 camera at 3.5m gave a reading of 35.5°C while the SC2000 read 36.5°C.
- The judge trial showed a high correlation of 0.96 for temperature interpretation across the different judges.
- The weaned calf trial showed a high correlation between the body weights of the animals on the different days (0.92, P<0.01) and between the two consecutive eye thermographs taken consecutively (0.94, P<0.01). However, correlations comparing the different days were low and inconsistent across the two weeks (0.42 and 0.30, P<0.01 for the eye on the first day compared to the eye on the second day in the two weeks, respectively).
- The exercise trial revealed a noticeable increase in temperature following the exercise. The hind foot, with a baseline temperature of 32.1°C, had risen to 35.1°C, post-exercise.
- The drug trial demonstrated a decrease in temperature after the xylazine administration (hind foot temperature decreased from 35.8°C to 34°C) and then an increase in temperature (35.6°C), upon the administration of atipamezole.
- The forced wind caused a decrease in the temperature of many different parts of the body as time went by with the fan on. The hind foot started at 33.6°C and decreased to 30.1°C while the fan was on. Once the fan was turned off, the temperature returned back to 33.5°C, Figure 2.
The results for the two types of debris are in progress.
The Bottom Line
There were differences in the infrared radiation captured by cameras when cattle were subjected to different conditions. These factors should be taken into account when infrared analyses are performed. The choice of equipment and accuracy of the image analysis are also key factors for successful use of this technology in the assessment of livestock.
Ontario Cattleman Association, Agriculture Adaptation Council, Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs, Beef Cattle Research Council and Agri-Food Canada.
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|Author:||Melissa Lim, Yuri Montanholi and Steve Miller - Centre for Genetic Improvement of Livestock, Dept. Animal and Poultry Science/ University of Guelph|
|Creation Date:||09 May 2013|
|Last Reviewed:||09 May 2013|