Feather retention during defeathering – impact of carcass rigor mortis.

Authors: Harris, Caitlin; Buhr, Richard - Jeff

Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/29/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The postmortem onset of rigor mortis in the skeletal muscles of broilers results in significant carcass stiffening within 30 min after death and can be accelerated at elevated carcass temperatures. Postmortem stiffness of the legs and wings results in the legs extended in the shackles while the wings are pulled closer to the body over the breast (contraction of the Pectoralis), resulting in an increase in the gap between the elbows. Although rigor mortis occurs in the smooth muscles that move the feathers within the follicles, this results in minimal changes in the Feather Retention Force (FRF) required to remove the feathers from the follicle. FRF is not substantially altered by the methods of electrical or controlled atmosphere stun/kill systems when measured antemortem, perimortem, or postmortem (within typical processing times less than 10 min), resulting in relatively small changes at 12%. In comparison, the major impact of scalding resulted in a FRF reduction of greater than 80%. The removal of feathers from the feather follicle requires the separation of the squamous cell layers of the outer feather follicle sheath from the inner feather sheath. Scalding provides moist heat to the feather follicles within the skin that loosens this connection and spraying warm water during picking continues the thermal process. Scalding duration can be shorter at 90 s when using higher temperatures (hard scalding 60 to 66C / 140–150F) than for lower temperatures at 180 s (soft scalding 54 to 58C / 129–136F), but both scalding methods result in inducing the separation of the feather from the feather follicle. Cylinder-shaped rubber picker fingers with ridges are used to grasp the feathers during picking are variable in length and stiffness to accommodate the type of poultry, carcass weight, and line speeds. Carcasses in rigor-stiffness during picking are less flexible, allowing minimal twisting that results in retained feathers on the sides of the carcass between the wings and the legs, and between the legs in over the abdomen. Elevating scalding temperatures, prolonging scalding duration, or narrowing the gap between the picker fingers results in unacceptable carcass damage and broken bones without removing the remaining feathers. There are typically a series of picking units that are configured at first a rough followed by finishing pickers. FRF increases with bird age and maturity but varies greatly by feather location on the carcass with the highest for flight feathers (remiges of the wing and rectrices of the tail) of up to 2 to 4 Kg depending on the species. Processors have added quill pullers consisting of counter rotation bars to grasp and remove these feathers without causing carcass damage.