VOCAL QUALITY IS CORRELATED WITH LEVELS OF STRESS HORMONES IN DOMESTIC PIGS

Our study examined whether vocalizations of domestic pigs Sus scrofa d omestica provide reliable cues for particular endocrine stress respons es. To induce stress responses, we separated subjects individually fro m groupmates (SEP) and controlled potential effects of motor activity by a second treatment in which subjects were also immobilized (SEP + I M). We analysed blood samples taken at short intervals via an indwelli ng catheter for titres of stress hormones to estimate endocrine stress responses. To identify behavioural responses we analysed recordings o f vocalizations and non-vocal activities. Data evaluation yielded the following results. Multi-parametric sound analysis enabled us to disti nguish four categories of vocalizations within treatments. Increasing rates of 'squeal-grunts' indicated increasing plasma levels of adrenal ine, whereas the rates of 'grunts' decreased when the levels of cortis ol increased. Acoustic parameters within the vocal categories distingu ished did not correlate consistently with levels of any of the measure d stress hormones; thus, our results show that peripheral endocrine st ress responses are accompanied by changing rates of specific types of vocalizations. These relationships remained consistent, even when subj ects' motor activity was restricted. Our results suggest possible effe cts of central stress reactions on both the control of vocalization an d the activation of endocrine stress responses.