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epi@vetmed.fu-berlin.de
The Mouse Grimace Scale (MGS) is a coding system for facial expression analysis of pain in mice and is widely accepted as welfare indicator. To facilitate and improve the use of the MGS, we aimed to develop a facial expression recognition software for mice. To this end, we utilized an image dataset of adult male and female C57BL/6JRj mice, that were either untreated, anesthetized (with isoflurane or ketamine/xylazine) or castrated (under isoflurane anaesthesia, meloxicam, lidocaine/prilocaine). The dataset was divided into two categories, i.e. “post surgical/anaesthetic effects present” and “no post-surgical/anaesthetic effects present”. Abinary classifier was trained to differentiate between the two categories. We used three convolutional neural network (CNN) architectures (two pre-trained state of the art deep CNN: ResNet50 and InceptionV3; one CNN of our own design without pre-training). When the network was provided multiple images per mouse, an accuracy of up to 99% was achieved. A feature visualization technique (Deep Taylor decomposition) indicated that the decision of the network was mainly based on image areas depicting the mouse faces. Our first steps towards a fully automated facial expression recognition software contributes to refining pain and stress assessment in laboratory mice.