Infrared thermography as a non-invasive method to quantify the heat stress response in weaned piglets after road transport in a semi-arid region

Heat stress (HS) is one of the main factors associated with welfare concerns during animal transport. The use of infrared thermography (IRT) for digitally monitoring HS in weaned piglets during transportation in a semi-arid region was investigated in the present study. A total of 60 focal piglets (25 ± 2.3 kg) were evaluated across five journeys of standard pigs-weaned loads in Ceará state, Brazil. Upon arrival at the designated farm, the piglets’ respiratory rate (RR, breaths/min), rectal temperature (RT, °C), and salivary cortisol concentration (SC, ng/mL) were measured. Furthermore, the piglets’ body (BT, °C) and ocular (OT, °C) temperatures were measured using IRT. The load’s thermal assessment was monitored for each journey using Temperature-Humidity Index (THI). The correlation between the variables and the thermal images of BT and OT were evaluated using Pearson’s coefficient analysis and agreement using Bland-Altman diagrams (P < 0.05). The study revealed a strong positive correlation between BT and OT with the piglets’ RT (BT with r = 0.78; OT with r = 0.968) and THI (BT with r = 0.7378; OT with r = 0.8115). Additionally, OT showed a strong positive correlation (r = 0.749), while BT showed a moderate correlation (r = 0.691) with the animals’ RR. On the other hand, BT and OT had a low correlation with salivary cortisol. The Bland-Altman analysis demonstrated that the use of IRT exhibited practically no bias (BT = 0.1249 °C and OT = 0.02075 °C) and showed reduced limits of agreement with RT measurements. These results provide evidence that infrared thermography technology can aid technicians and pork transport companies in estimating the physiological condition of heat stress in piglets weaned in a semi-arid region, serving as a mechanism to protect animal welfare.