Table 7.

ABMs for the assessment of heat stress in sheep during loading/unloading and transit

ABM	Definition and interpretation of the ABM
Rectal temperature	Definition: Rectal temperature is measured as an indicator of core temperature. Rectal temperature of sheep varies between 38.3°C and 39.9°C under thermoneutral conditions (Goodwin, 1998; Kearton et al., 2020). 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. Sheep lose approximately 20% of total body heat via respiratory moisture in a neutral environmental temperature (12°C). The moisture loss increases and accounts for approximately 60% of the total heat loss at high ambient temperature (35°C) (Thompson, 1985). An increase in the ambient air temperature from 18°C to 35°C is accompanied by significant increases in rectal temperature in sheep (Marai et al., 2007).
Panting	Definition: The first phase of panting is characterised by rapid, shallow breaths associated with an increase in respiratory rate resulting in an increase in respiratory volume (Hales and Webster, 1967). Open‐mouth panting is related to the second phase of gasping which is characterised by slower and deeper breathing, associated with open‐mouth gasping and a greater increase in respiratory volume than that observed in the first phase of gasping (Hales and Webster, 1967). Interpretation: Rapid panting is a response to hot environmental conditions or acute physical exercise (Lees et al., 2019).
Respiratory rate	Definition: Frequency of breathing, usually measured as the number of breaths that can be counted according to the flank movements per minute (Da Silva et al., 2002). Interpretation: Respiration rate increases with body temperature in order to maintain homeostasis.
Salivation	Definition: The secretion of biofluid by the three major salivary glands located in the mouth ‐ paroid, submandibular and sublingual ‐ together with the secretions from the minor submucosal glands of the oral cavity (Proctor, 2000). Interpretation: Intense salivation is one of the clinical signs of heat stress in sheep (Dos Santos et al., 2019). When animals experience heat stress they exhibit profuse salvation or drooling (Caulfield et al., 2014).
Sweating	Definition: Secretion of fluid or moisture from the sweat glands to the surface of the skin. Interpretation: At high temperatures, evaporative cooling is the main mechanism for heat dissipation in most mammals (Blackshaw and Blackshaw, 1994) and is the only form of heat loss once the ambient temperature exceeds the skin temperature (Cunningham, 2002). When the effective temperature increases above the comfort zone, the animals will start to sweat. Further increases in the effective temperature will see increased rates of sweating. Sweating can also be due to other factors such as exercise or stress.

ABM: animal‐based measure.