Vocal communication is known to be an important part of communication in both wild and domestic pigs. Calls encode information about the emotional state of an animal and may reflect its need for social and non-social resources. Recently, analysing the vocalisation of farm animals has become an increasingly important tool for evaluating animal welfare. The objective of this study was to test whether the vocalisation of fattening pigs can be used to assess their adaptability to ambient temperatures. The pigs were kept in conditions comparable to those of commercial housing and were exposed to high and low temperatures for several days. The pigs were observed at body weights of 25-35, 50-70 and > 80kg. Vocalisations were recorded during 23.00 to 5.00 h and analysed using an artificial neural network. The results indicate with decreasing temperatures, huddling of pigs to be increased. The increase of huddling was also accompanied by an increase in high-vocalisation. Pigs produce more high-frequent vocalisation and huddled less with increasing weight. The findings of this study suggest that huddling results in a state of discomfort in at least medium and heavy pigs and this is reflected by changes in vocal behaviour. Smaller pigs seem to be less affected by huddling than heavy pigs. In this study, high frequency vocalisation that was produced in situations of disturbed lying behaviour proved to be a powerful indicator for thermoregulatory reactions to low ambient temperatures in medium-weight and heavy pigs. This opens up the possibility to use high-frequency vocalisation for an automatic acoustic monitoring of the behavioural adaptation of fattening pigs towards cold. The use of acoustic monitoring will potentially help animal caretakers to optimize the environmental control.