SOUND AVOIDANCE BY DOMESTIC PIGS DEPENDS UPON CHARACTERISTICS OF THE SIGNAL

Habituation to novel, loud and predictable sound stimuli appears to oc cur in pigs, though this has not been unequivocally demonstrated. In a ddition, different types of sound may be more or less aversive; humans find unpredictable, intermittent sound more aversive than constant so und. The aim of this study was to test these two hypothesis in pigs. T wo groups of 12 pigs, weighing 25 kg, were individually exposed to a t est sound in a modified unsignalled one-way avoidance procedure. The t est sound for the first group was a recording from an animal transport er played at 84 dB(Lin), with a rise time of 2 s (uniform, U). For the second group, silent fragments, 59 dB(Lin), were randomly inserted in to the recording, played at 86 dB(Lin), and the rise time was changed to < 0.1 s (Intermittent, I). A total of 40 consecutive, 5 min tests w ere carried out for each pig, 20 control and 20 with sound present. So und present tests were arbitrarily split into three groups, comprised of tests 1-6, 7-12 and 13-20, for analysis. Pigs did not significantly avoid the uniform sound in any of the groups of tests, though they di d increase their performance of active behaviour when the sound was fi rst introduced (Control test no. 20, 15% of behaviour scans; Sound tes t no, 1, 37% of behaviour scans; p < 0.01). The intermittent sound was significantly avoided during all three sets of sound tests (Mean perc entage of time spent avoiding sound area: Control tests 2-20, 35%; Sou nd tests 1-6, 67%; Sound tests 7-12, 73%; Sound tests 13-20, 66%, p < 0.05). These pigs also showed significant increases in active behaviou r during the first sound test (Control test no. 20, 14% of behaviour s cans; Sound test no. 1, 42% of behaviour scans; p < 0.01), The results suggest that aversion is dependent on characteristics of the sound, s uch as uniformity, rather than neophobia, (C) 1998 Elsevier Science B. V. All rights reserved.