Validation of an automated system for at-slaughter assessment of footpad dermatitis and hock burn in broiler chickens

The automated assessment of footpad dermatitis and hock burn via camera systems at the slaughterline could allow continuous monitoring of these important welfare indicators in broiler chickens. This study aimed to compare the performance of a camera system (ChickenCheck software, CLK GmbH) against three human assessors. Footpad dermatitis (4 point scale based on relative size of the lesions compared to the footpad) and hock burn (3 point scale based on absolute size of the lesions) were scored on both the left and right foot and hock according to severity from images captured by the camera system. A total of 50 images (100 feet and hocks) were used in the training dataset used to train the human assessors and 500 images (1,000 feet and hocks) were used in the validation dataset to determine measures of agreement and reliability for the discrete scoring system. Additionally, 100 images were used for lesion annotation (200 feet and hock) to determine the agreement between the camera system and the human assessors in capturing the total area affected by lesions. Despite showing substantial to good intra-observer reliability (kappa: 0.78-0.98) and moderate to substantial inter-observer reliability (kappa: 0.46-0.66) during training, the human assessors showed fair to moderate agreement (kappa: 0.33-0.47) for footpad dermatitis and hock burn when the dataset included a larger number of images with greater variation in lesion severity and appearance. However, the human assessors showed moderate to substantial agreement with the scores assigned by the camera system (0.60-0.70). More importantly, human assessors and camera system are highly correlated when it comes to indicating the size of lesions on the footpad (R 2: 0.93) and hock burn (R 2: 0.97), suggesting that lesions are correctly annotated by the camera system. However, the small but systematic differences found in the size of the affected area of footpad dermatitis (+2.47%) and hock burn (-0.38 cm 2) by the camera system compared to the human assessors need to be addressed to further improve the performance of the automated system.