Behavioural and physiological responses of pigs to sound

Sound is a potential stressor to pigs throughout their lives, The following two studies examined the behavioural acid physiological responses of pigs to both artificial and real sound. In the first study, piglets (n = 8) were exposed to artificially generated sounds, nominal intensities of 85 or 97 dB(Lin), and frequencies of 500 Hz and 8000 Hz for 15 min, during an hour experimental session, In the second study the piglets (n = 8) were exposed to 20 min of four sounds: farm recording, Leq 80 dB(Lin); transport recording, Leq 83 dB(Lin); abattoir recording, Leq 84 dB(Lin) and white noise, Leq 89 dB(Lin). In both studies piglets were exposed to the sounds in an arena to which they had previously become accustomed and a companion pig was present in the experimental room. The behaviour and heart rate of the piglets were recorded pre-, during and post-exposure to all the sounds in both studies. In addition observations were also made in a control session with no sound stimuli, In both studies an increase in heart rate (maximum 20 beats min(-1)) was observed for the first 15 min of exposure to sound (P < 0.05), when compared with controls. An increase in ambulation score (control 4.4 vs 97 dB(Lin) 20.2) due to sound exposure was only observed in Study 1 (P < 0.05). Greater increases were found when the pigs were exposed to the higher frequency and higher intensity in Study 1 (P < 0.05). In the second study small differences were found between the treatments, with the transporter causing the greatest increase in heart rate (P < 0.05) and the greatest reduction in ambulation score (P < 0.05). When the specific behaviours of the piglets were compared there was no difference between the different treatments in Study 2 (P < 0.05), however sound exposure in general changed the behaviour of the pigs from resting to aroused and attentive (P < 0.05), The results from these two studies suggest that sound can activate the pigs' defence mechanisms, though habituation occurs when no immediate danger or threat is identified, and that the manifestation of this response depends on properties of the sound stimuli.