Behavioral measurements as sensitive non-invasive indicators to assess the thermoregulatory response in weaned piglets

A total of 96 piglets (38 days post-weaning) were used to examine the thermoregulatory response towards warm environmental conditions and to identify indicators for detecting the impact of high environmental temperatures on young pigs. The trial was conducted on an experimental farm equipped with 4 identical rooms: i) two rooms remained in thermally neutral conditions (TN, 22.85 °C ± 0.41 °C; 60.90% ± 4.31% humidity, THI 74). The heat challenge period was performed from day 38 until day 41 post-weaning. Then, three experimental groups were established: an HT group located in HT rooms, a Control group (CON), and a pair-fed group (PF) in TN rooms. The average feed intake was recorded daily during the challenge period. Blood and saliva samples were collected just before and at the end of the challenge, and liver samples were collected after the euthanasia of the pigs. Cortisol concentration was measured in plasma and saliva pre- and post-challenge (day 38 and 42 post-weaning). Plasmatic haptoglobin concentration and activities of glutathione peroxidase, catalase, and superoxide dismutase were measured on day 42. Gene expression of 16 genes related to inflammation, oxidative stress, and apoptosis was assessed in the liver samples. Additionally, respiration rate and behavioral observations, including piglets' position in the pen (front, middle, rear), posture (standing, lying down, sitting, among others), and behavior (feeding, drinking, panting, nostril movements, resting, among others), were conducted over the three days of the challenge period. Feed intake was decreased by 23.4% in the HT, a reduction applied to the PF group to isolate the temperature effect. No significant differences were found between the treatment groups regarding cortisol (plasmatic and salivary), haptoglobin concentration, antioxidant enzyme activities, and liver gene expression levels. Concerning behavioral measurements, differences were observed between treatments (P