Hot-water spraying is a sensitive test for signs of life before dressing and scalding in pig abattoirs with carbon dioxide (CO2) stunning

Abstract

This study investigated the benefits of hot-water spraying (HWS) as a diagnostic test to verify the absence of signs of life (SOL) before scalding in pigs slaughtered with carbon dioxide (CO 2 ) stunning. A total of 37 108 finishing pigs from five German abattoirs (A to E) operating at 55 to 571 pigs per hour were assessed. Suspended pigs were sprayed onto the muzzle, head and front legs (143 to 258 s post sticking for 4 to 10 s, 57°C to 72°C). Any active movements during HWS were rated as positive test outcomes. In comparison, SOL were considered to be absent if a subsequent manual examination was negative and no active movements were observed following HWS. The incidence of pigs with activity during hot-water spraying (PWA) was restricted to two abattoirs (B: 0.25%; D: 0.02%; A, C, E: 0.00%). PWA showed movements of facial muscles (88%), mouth opening (78%), righting reflex (63%), isolated leg movements (35%) and vocalization (4%). The manual examination was positive in 71% of PWA (corneal/dazzle reflex: 67%/53%, nasal septum pinch: 33%), whereas all inactive pigs tested negative ( P < 0.001). The sensitivity for HWS as a test for SOL was calculated as 100%, dropping to 75% when only obvious and strong movements were taken into account. The specificity was >99.9% in either case. Any positive manual findings as well as any respiratory activity were instantly terminated using a penetrating captive bolt. Active movements triggered by the shot were shown to be an indicator for SOL (P < 0.001). Video analyses revealed that spontaneous movements (SM) following sticking were present in 100% of PWA as opposed to 3.1% in pigs without such activity (controls). Results for different categories of SM in PWA v. controls were as follows: 100% v. 2.6% for mouth opening, 16.0% v. 0.1% for righting reflex and 22.0% v. 0.9% for isolated leg movements (all P < 0.001). First mouth opening after sticking was observed later in PWA (28 ± 24 v. 10 ± 7 s), but mouth openings were observed for a longer period of time (141 ± 44 v. 27 ± 25 s) (both P < 0.001). PWA with shorter mouth-opening intervals showed higher movement intensities during HWS and more positive manual findings (P < 0.05). We conclude that HWS is a promising test for SOL. SM and sustained mouth opening in particular are indicators for compromised animal welfare and affected pigs should be shot by captive bolt.

Consciousness, unconsciousness and death in the context of slaughter. Part II. Evaluation methods

“…In another study, after stunning and sticking, certain pigs moved when they received a nociceptive stimulus due to a hot water spray. These same pigs showed also eyelid closure upon touching the cornea or when a light was shone in the eye, suggesting that the response to the hot water spray was indicative of a certain degree of brainstem functioning (Parotat et al, 2015). The interest of the test is that it can be automatized.…”

“…Further studies are needed to evaluate the exact relationships between various nociceptive stimuli and brain functioning. For example, in the above study, the same pigs were also tested using a nasal septum pinch but only one third of the pigs that moved when they received the hot water spray responded to the nasal septum pinch (Parotat et al, 2015). Similarly, immediately following a neck cut of non-stunned sheep, the withdrawal response to an ear pinch was lost, while breathing and the corneal reflex were still present and the EEG indicated the presence of consciousness (Verhoeven et al, 2015b).…”

“…To test the response to a pain stimulus, the withdrawal response following a pinch (of the comb, the ear tips, or the nasal septum for example), a skin prick with a hypodermic needle, or spraying with hot water may be tested (Limon et al, 2010;McKinstry & Anil, 2004;Parotat, von Holleben, Arnold, Troeger, & Luecker, 2015;Verhoeven et al, 2015b). Currently, the pain test needs further research to improve its discriminatory power.…”

“…Similarly, the absence of a response is not always indicative of unconsciousness. These recent results are promising but further research is needed to fully explore the relationship between reactions to different pain stimuli and brain functioning, while aiming for tests that aim to cause as little pain as possible (Parotat et al, 2015).…”

Editorial: Pigs crying, silent fish and other stories about animal welfare assessment

“…However, stunning is not always carried out effectively, and therefore it is essential to check that an animal is properly stunned before bleeding it. Parotat et al propose to spray hot water on the nose of a stunned pig and to score its movements to rapidly check that the animal is unconscious (Parotat et al, 2016). However, it is also relevant to note that immobilisation does not equal unconsciousness.…”