Construct validation of behavioral indices of isolation stress and inflammatory nociception in young domestic fowl

Isolation from conspecifics can elicit a variety of behavioral responses in young domestic fowl that include increased vocalizations (VOC), ventral recumbency posturing (VRP), hypoalgesia, and hyperthemia. During tests of acute inflammatory nociception, chicks not only display several pain-related behaviors (i.e., footpecks and lifts), but also VOC and VRP. However, systematic evaluation of whether these behaviors reflect converging indices of stress and nociception remains to be conducted. In two separate experiments, 7-day-old chicks received intraplantar formalin (0.05%) or saline (0.05 ml) and were placed in sound-attenuating chambers with or without two conspecifics for a 3 min observation period. The following measures were recorded: VOC, footlift frequency (LFT), and duration (DUR, Experiment 2 only), pecks (PKS), ventral recumbency latency (VRL), body temperature (BTMP), and body weight (WGT). Principal component analyses revealed the presence of two oblique and nonmonotonically related components, one consisting of pain-related measures (i.e., LFT, DUR, and PKS) and the other consisting of stress-related measures (VOC, VRL, and BTMP). A third component, consisting of BTMP and WGT ostensibly reflects maturational variability in thermoregulatory capability. These findings support the construct validity of these behavioral indices of isolation stress and inflammatory nociception and are consistent with the notion of stress effects on nociceptive processing.