Infrared thermography detects febrile and behavioural responses to vaccination of weaned piglets

Abstract

An automated, non-invasive system for monitoring of thermoregulation has the potential to mitigate swine diseases through earlier detection. Measurement of radiated temperature of groups of animals by infrared thermography (IRT) is an essential component of such a system. This study reports on the feasibility of monitoring the radiated temperature of groups of animals as a biomarker of immune response using vaccination as a model for febrile disease. In Study A, weaned pigs were either treated with an intramuscular vaccine (FarrowSure Gold), a sham injection of 0.9% saline or left as untreated controls. An infrared thermal camera (FLIR A320) was fixed to the ceiling directly above the pen of animals, and recorded infrared images of the treatment groups at 5 min intervals. The effect on temperature of the spatial distribution of pigs within the pen was significant, with higher temperatures recorded when pigs were grouped together into a single cluster. A higher frequency of clustering behaviour was observed in vaccinated animals compared with controls during a period of the afternoon ~4 to 7 h post-vaccination. The daily mean of the maximum image temperature was significantly higher in vaccinated animals compared with control and sham-treated animals. In the vaccination treated group, the 24 h mean of the maximum temperature was significantly higher during the post-vaccination period compared with the 24 h period before vaccination. Increased temperature in the vaccinated animals occurred from ~3 h, peaked at ~10 h, and remained elevated for up to 20 h post-vaccination. In Study B, the effect of prevalence was tested in terms of the difference in maximum temperature between control and vaccination days. A thermal response to vaccination was detected in a pen of 24 to 26 animals when <10% of the animals were vaccinated. The results support the concept of radiated temperature measurements of groups of animals by IRT as a screening tool for febrile diseases in pig barns.

Keywords: febrile response; infrared thermography; pigs; vaccination.

Figure 1

Examples of the spatial distributions of pigs within the pen showing cluster score categories 1 to 7. Cluster scores of 1, 2 and 3 were combined to give a high cluster score (HCS) category, and cluster scores of 4, 5, 6 and 7 were combined to give a low cluster score (LCS) category.

Figure 2

The numbers of deviations in high cluster score (HCS) and low cluster score (LCS) categories for treatment groups in Study A. Positive values show a greater number of observations in that cluster score (CS) category than would be expected from χ ² distributions. Negative values show lower than expected numbers of observations.

Figure 3

The percentages of high cluster scores (HCS) over 30 min intervals in vaccinated animals and a combination of all control images (Con, Vac Con and Sham Con) in Study A.

Figure 4

The mean of the maximum pig temperature for 30 min intervals relative to vaccination and sham injections (Time 0) in all treatment groups in Study A. The control group of animals are designated as Con, and the Vac Con and Sham Con were images collected on control days for the Sham and Vac treatment groups. Sham Trt and Vac Trt were images collected on Sham and Vac treatment days.

Figure 5

The mean of the Temp Diff parameter for pig maximum temperature at each 5 min sampling interval for all levels of prevalence in Study B. A positive value meant that the temperature in the post-vaccination image was higher than in the pre-vaccination image.

Figure 6

The relationship between prevalence and the Temp Diff parameter for pig maximum temperature in Study B.