Table 7.

ABMs selected for the assessment of heat stress in pigs during preparation, loading/unloading, transit and journey breaks

ABM	Definition and interpretation of the ABM
Respiratory rate	Definition: Breathing rate. Usually measured by counting the movements of the flank from direct observation and converting this into breaths per minute (BPM). Interpretation: Heat stress leads pigs to show increased respiration rates until reaching panting. Respiration rate increases with body temperature in order to maintain homeostasis (Brown‐Brandl et al., 2001; Bjerg et al., 2020).
Rectal temperature	Definition: A proxy for the body temperature of the pig as measured by a thermometer inserted in the rectum (Yundong, 2012). Interpretation: Body temperature rises during heat stress when the physiological and behavioural mechanisms for the dissipation of heat can no longer maintain equilibrium because of heat gained from excessive environment heat combined with metabolic heat production.
Panting	Definition: Short breathing carried with the mouth open (Bracke et al., 2020). The first phase of panting is characterised by rapid, shallow breathing called thermal polypnea, associated with an increase in respiratory rate. This shifts to a second phase characterised by slower and deeper breathing, named thermal hyperpnea characterised by an increase of alveolar ventilation rate. Interpretation: Evaporation of water by panting is the primary form for pigs to loose heat at high temperatures (Huynh et al., 2005). Panting is considered a physical sign of stress and it is associated with dissipation of excess heat and/or fatigue.
Skin discoloration	Definition: Changes from light to redder colour of the skin with a transient blotchy appearance (Kephart et al., 2010). Interpretation: It is considered a physical sign of stress due to the effort related to physical activities such as loading/unloading (Pilcher et al., 2011).

ABM: animal‐based measure.