Nociceptors in the legs of poultry: Implications for potential pain in pre-slaughter shackling

Shackling of commercial poultry involves the insertion of each leg into par allel metal slots and holding the bird inverted for a period of time before stunning and slaughter. Nociceptors signalling noxious stimulation of the skin have been identified in the beak and feathered skin but not in the sca ly skin of the leg. The physiological properties of the C-fibre mechanother mal (CMT) nociceptors in the skin over the tarsometatarsus in the lower leg were studied in response to quantitative mechanical stimulation. The elect rical activity was recorded from single C-fibres dissected from the parafib ular nerve in anaesthetized animals. The receptive fields of these receptor s were small and spot-like, measuring in the region of 1-3 mm in diameter. The threshold to mechanical stimuli ranged from 0.8-15 g using von Frey fil aments, and from 3-33 g using a 0.5mm probe mounted on a feedback-controlle d stimulator. Stimulus response curves using a ramp-and-hold stimulus were recorded for a number of fibres. After comparing these threshold measuremen ts and the stimulus response data with previous measurements of the force a pplied to the legs during shackling, it was concluded that shackling is lik ely to be a very painful procedure.