The influence of domestic piglets' (Sus scrofa) age and test experience on the preference for the replayed maternal nursing vocalisation in a modified open-field test

The nursing vocalisation of lactating sows is an important part of the complex nursing and suckling behaviour of domestic pigs (Sus scrofa). It helps to lead the young through the several phases of a nursing episode. A total of 135 suckling piglets were investigated regarding their reactions to different vocalisations and sounds successively replayed in combined choice/open-field experiments. Two piglet samples were used to determine the impact of age (sample 1: weeks 1 and 5, n=93) and previous test experience of naive older piglets (sample 2: week 5, n=42) on their behavioural responses. In the 1st week after birth, the nursing vocalisation of sows released an initial generalised approach and contact response in the young, indicating high motivation to gain nutritional or social support. Close to the sound source, the piglets then strongly preferred the nursing vocalisation produced by their own mothers compared to that produced by another, unrelated and unfamiliar sow, or an artificial sound composed of similar frequencies as the nurse grunting, or a control without sound. However, at the end of the suckling period (5-week-old piglets) no clear differences in the reactions to the sounds could be identified. Moreover, the lack of a clear response at week 5 seems largely independent of any earlier test experience of the piglets. As well in the 1st as in the 5th week the piglets showed a decrease in open-field activity when sow grunting was present, indicating that the replay of the nursing vocalisation might have some calming effect.