Assessment of the aversion of hens to different gas atmospheres using an approach-avoidance test

A Critical Review of Electrical Water-Bath Stun Systems for Poultry Slaughter and Recent Developments in Alternative Technologies

“…The humaneness of exposure to low concentrations of CO 2 has been evaluated, and it has been argued that CO 2 levels of 30% or less may not be much more aversive to inhale than the inert gas argon. This was demonstrated initially by Webster and Fletcher (2004), who showed that nearly as many moderately food-deprived chickens would enter a feeding chamber and lose posture (an early sign of onset of unconsciousness) due to gas exposure when the chamber was filled with 30% CO 2 in air compared with argon. Similar results were subsequently reported in another study testing the aversiveness of several different gas mixtures (CO 2 in air at concentrations ranging from 10 to 70%, CO 2 in nitrogen ranging from 25 to 40% with 30% oxygen, and 100% argon and 100% nitrogen) by exposing broiler chickens to a 10-s pulse of gas while the birds fed.…”

“…In behavior experiments, both turkeys and chickens willingly entered a chamber filled with argon in order to access food (Raj, 1996;Webster & Fletcher, 2004). In contrast, physiological and behavioral evidence suggests that CO 2 may be unpleasant and possibly very distressing to inhale as it is an acidic, pungent gas at high concentration.…”

“…Further, the thrashing of one bird may frighten or physically harm, albeit briefly, other birds who have not yet lost consciousness. These convulsions can be aesthetically unpleasant to human observers and also involve powerful leg and wing movements (Webster & Fletcher, 2004). Broken wing bones caused by convulsions can also reduce the quality of the carcass.…”

A mobile modified-atmosphere killing system for small-flock depopulation

“…Although control of the chamber atmosphere would be more variable than with an automated gas control system, a trained individual could manually operate an MAK unit quite well [7], and the risk of exposing birds to concentrations of CO 2 that might be irritating might not be excessive [8]. Chickens do not appear to find concentrations of CO 2 as high as 60% to be greatly aversive [26,27]. The most feasible design for a mobile MAK small-flock depopulation unit, therefore, may differ somewhat from the unit tested in this study, depending on the trade-off of costs, convenience, and ethical considerations as worked out between the manufacturer and customer.…”

Slaughter of animals: poultry

“…Animals, including birds, do not have intrapulmonary chemoreceptors to detect inert gases and therefore do not show any aversion during initial exposure to hypoxia/anoxia induced with nitrogen, argon or their mixtures. Webster and Fletcher () reported that, in an avoidance test, hens showed the least number of stops and retreats during approach to argon atmosphere when compared with carbon dioxide, and the behaviour of the birds has been described as very similar to that observed in air. In addition, the highest percentage of the test hens was stunned in the chamber when argon was presented, whereas, most of the hens hesitated to enter the chamber containing carbon dioxide and were therefore stunned in the corridor leading to the chamber.…”