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Abstract

Our study examined whether vocalizations of domestic pigs Sus scrofa domestica provide reliable cues for particular endocrine stress responses. To induce stress responses, we separated subjects individually from groupmates (SEP) and controlled potential effects of motor activity by a second treatment in which subjects were also immobilized (SEP + 1M). We analysed blood samples taken at short intervals via an indwelling catheter for titres of stress hormones to estimate endocrine stress responses. To identify behavioural responses we analysed recordings of vocalizations and non-vocal activities. Data evaluation yielded the following results. Multi-parametric sound analysis enabled us to distinguish four categories of vocalizations within treatments. Increasing rates of ‘squeal-grunts’ indicated increasing plasma levels of adrenaline, whereas the rates of ‘grunts’ decreased when the levels of cortisol increased. Acoustic parameters within the vocal categories distinguished did not correlate consistently with levels of any of the measured stress hormones; thus, our results show that peripheral endocrine stress responses are accompanied by changing rates of specific types of vocalizations. These relationships remained consistent, even when subjects' motor activity was restricted. Our results suggest possible effects of central stress reactions on both the control of vocalization and the activation of endocrine stress responses.