Detection of heat produced during roughage digestion in ruminants by using infrared thermography

Abstract

The present study aimed to establish the relationship of infrared thermography (IRT) with fermentation dynamics in ruminants, and to initiate the development of a method that allows associating these images with the heat produced during feed digestion. The experiment was conducted at APTA, Brazil. Twenty-four Jersey heifers (mean liveweight of 221.25 ± 59.41 kg) were subjected to the following treatments: 30R (30% corn silage and 70% concentrate), 50R (50% corn silage and 50% concentrate) and 70R (70% corn silage and 30% concentrate) in a Latin square design. The diet (corn silage + concentrate) was offered at 3% of liveweight from 0800 hours to 1400 hours. Infrared images were collected from the whole body on the left and right sides, from the eyes, from the left foreleg on the cranial and caudal side, and from the forehead. IRT images were taken at 2-h intervals for 12 h (from 0600 hours to 1800 hours) and 24 h (0600 hours of the following day) after the beginning of feeding and so on. Physiological parameters were obtained at the same time as the IRT were taken. Ruminal parameters were collected after 4 h of feeding. The thermograms of the right (P < 0.001) and left flank (P < 0.001) differed among sampling times, with an increase in temperature until 1400 hours and a reduction thereafter. The temperatures on the right (P = 0.037) and left (P = 0.017) flank were higher in animals consuming the 50R diet and lower in those consuming the 70R diet. When the 50R diet was offered, the heifers exhibited higher dry-matter intake (P < 0.001), neutral detergent fibre (P < 0.001), non-fibrous carbohydrates (P < 0.001) and total digestible nutrients (P < 0.001). A decrease in the concentrations of butyric acid (P = 0.042), isobutyric acid (P = 0.001), isovaleric acid (P = 0.019) and ammonia nitrogen (P = 0.001) in the rumen fluid of heifers was observed with an increasing dietary roughage level. Infrared thermography was able to detect differences in the body temperature of animals associated with different fibre proportions in the diets. However, the magnitude of these differences was small and further research is needed to investigate the application of IRT to the detection of possible differences in the body temperature of ruminants as part of the digestive process.