Struggling responses of broiler chickens shackled in groups on a moving line: effects of light intensity, hoods, and `curtains'

Abstract

The vigorous struggling and wing flapping responses often shown by shackled chickens can compromise their welfare and seriously damage product quality. Their reduction would benefit the chickens, the farmers and the consumers. We have already shown that covering broilers' heads with an opaque hood virtually eliminated struggling when they were suspended individually from stationary shackles but the practical relevance of this finding is limited largely to those occasions when the health or growth rate of representative birds from a flock are examined. The present study moved a step closer to commercial conditions and focused on the responses of 42- to 44-day-old broilers when they were shackled in groups of three on a moving line, (observations were only carried out on the central bird in each trio). Struggling was assessed as a function of ambient illumination (<2, 5, 50 and 200 lx) in Experiment 1, the application of opaque hoods immediately before shackling in Experiment 2, or the suspension of a curtain from the overhead conveyor in Experiment 3. Unlike a previous finding obtained using individually tested birds and a stationary line ( Jones et al., 1997), struggling was less pronounced in Experiment 1 among broilers shackled under low rather than high light intensities. This finding is consistent with earlier suggestions that dim light has a `quietening effect'. In Experiment 2, covering the broilers' heads with an opaque hood before they were shackled reduced their struggling responses substantially below those shown by nonhooded controls regardless of whether the processing line was stationary or moving. These results extend our previous findings and confirm the potency of devices which preclude patterned vision in the induction and maintenance of immobility. There were no detectable effects of line movement per se. Struggling was significantly attenuated in Experiment 3 when a heavy curtain was suspended from the overhead conveyor so that it extended beyond the full length of the birds and rested against their breasts. This effect may have reflected the simulated continuation of a predatory encounter and/or the possibility that the heavy curtain was sufficiently inflexible to physically compromise struggling. A system that incorporated continuous tactile stimulation, a physical obstacle to wing flapping and head raising, and a device that precluded patterned vision might be particularly effective in minimising struggling and its damaging effects.