Analysis of pain-related vocalization in young pigs

The assessment of pain constitutes a major issue for animal welfare research. The objective of this study was to classify vocalizations during castration pain and to assess alterations in vocalizations under local anaesthesia. The alterations in vocalization were measured by multiparametric call analysis. A total of 4537 calls of 70 young pigs were evaluated. With the data of this study three call types are distinguishable (grunt, squeal, scream). A high percentage (94.64%) of calls that could be classified in one of the three call types during the castration process within the confidence level of 95% was found. The comparison of the occurrence of the call types during treatments gives evidence for pain-related use of screams. The piglets castrated without local anaesthesia produced almost double the number of screams as piglets castrated with anaesthesia. The comparison of the recorded sound parameters reveals the particular position of screams in the call repertoire of young pigs. Screams are significantly different in their sound parameters than grunts or squeals. Castration in comparison to mere restraint produced a comprehensive change in sound parameters, with castration calls becoming more extended and more powerful. The findings in this study also show differences in the effectiveness of the parameters which indicate pain. Parameters that describe a single event in a call, such as peak level or peak frequency give better results than parameters that describe an average, such as weighted frequency and main frequency. The research indicated that pain-related changes of calls in piglets can be identified. On the basis of the results, automatic classification of call types during management operations may be developed. This could contribute to objective animal welfare assessment.