Stunning with carbon dioxide gas (CO2) is used in turkeys (Meleagris gallopavo var domesticus) as an alternative to electrical water bath stunning. Investigations were carried out to assess the behavioural and clinical responses of turkeys stunned in a V-shaped CO2
tunnel while sitting in their transport crates as part of the usual slaughter routine in a commercial abattoir. The CO2 concentration in the tunnel rose from 27% at the first observation point (A) to 74% at point D and the transport time was 180 s. At window 1, 37.1% of the birds
showed head shaking, 3.7% deep breaths and 2.9% intensive wing-flapping and at window 2 the respective figures were 2.2, 18.4 and 6.2%. All birds appeared to have lost consciousness at the point of leaving the tunnel. Prior to shackling, 15 s after leaving the tunnel, 230 animals were tested
for both interphalangeal reflex and eyelid closure; 20.4% had an incomplete eyelid closure but none displayed an interphalangeal reflex. It would appear that the tunnel system we investigated stuns turkeys effectively within 180 s. However, the initial stunning phase of 40–105 s appears
to cause the animals distress, which is demonstrated by head shaking, deep breaths and wing flapping.