Identifying dead-on-arrivals (DOA) at shackling in a slaughter line gas stunning system for end-of-lay hens: Part II - Proof of concept for detecting simulated change in hock flexion resistance

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In this study, the simulated hock flexion resistance at which employees could consistently differentiate a stunned bird from a recently dead end-of-lay hen was evaluated. A mechanical apparatus was used with individually weighted levers, ranging in resistance from 66 to 485 gram-force (gf), in a random order. A reference lever was weighted at 120 gf, which is similar to that of stunned birds measured immediately after gas stunning. Each employee (n = 15) lifted each lever to an approximately horizontal plane and designated it as having less resistance or similar resistance to the reference lever (light) or greater resistance than the reference lever (heavy). Dominant and non-dominant hands were tested independently. For resistance of up to 300 gf, there was a significant (P ≤ 0.05) increasing curvilinear trend in the proportion of employees who considered the lever to be heavy, and a significant decreasing curvilinear trend in the proportion who considered the lever to be light. At greater than 300 gf, close to 100% of employees gave the designation heavy, and there was no significant (P > 0.05) change with any further increases in weight. It was concluded that employees could reliably detect hock flexion resistances of ≥ 300 gf as larger in magnitude than 120 gf.

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