Physiological responses of pigs to preslaughter handling: infrared and thermal imaging applications

Abstract

Loading, transport, unloading, lairage and stunning are the principle ante-mortem events that generate negative responses associated with stress in pigs. For this reason, it is important to verify the condition of animals throughout the supply chain in order to ensure their welfare and obtain, at the end of the slaughtering process, high-quality carcases and meat. Several studies have identified the indicators and samples that need to be taken into account to properly measure and evaluate the responses that these animals emit to the stressors involved. However, these procedures must be carried out quickly and by non-invasive means so as not to impede the flow of animals through the operations of loading, transport, unloading and lairage. Therefore, the objective of this review article is to analyse the stressful events that pigs experience during these events and discuss the use of the infrared thermography (IRT) as an alternative tool for measuring stress based on temperature changes on the surface of pigs' skin. We argue that infrared thermography can be used as a strategy to improve animal welfare during loading, transport, unloading and lairage by preventing fatigue and deaths, and decreasing negative impacts on meat quality, such as pale, soft and exudative (PSE), or dark, firm and dry (DFD) conditions.

Keywords: Pig welfare; abattoir; infrared thermography; skin temperature; transport.

Figure 1.

A pig with hyperthermia upon arrival at an abattoir

Figure 2.

Infrared thermographic changes in pigs upon arrival at an abattoir after transport for several hours. Thermograms on the left are of hogs that arrived at night (coldest time of the day, 18°C) at the abattoir with a journey of 4 hours. Blue areas (highlighted with white dotted lines) are distinguished, with temperatures between 22 and 25°C in peripheral areas such as auricular pavilion and snout; the pigs look fresh. In fact the highest temperatures seemed normal (36°C) in the eye and ear canal areas. In contrast, on the right side of the figure there are 3 thermograms of hogs that arrived at the abattoir at 1:00 p.m. (warmest hour of the day, 34°C), with a journey of 4 hours. White areas (highlighted with black dotted lines) that indicate very high surface temperatures (39 and 41°C) of the loin, face and forearm regions are distinguished. Hogs present hyperthermia, tachypnoea, and in some cases dyspnoea