Animal Welfare and Meat Quality Assessment in Gas Stunning during Commercial Slaughter of Pigs Using Hypercapnic-Hypoxia (20% CO(2) 2% O(2)) Compared to Acute Hypercapnia (90% CO(2) in Air)

SIMPLE SUMMARY: Animals must be stunned before slaughter to avoid fear, pain, and distress. In pigs, the most extensively used method is exposure to hypercapnia (high (>80%) concentrations of carbon dioxide (CO(2))). However, it produces irritation of the mucosa and a sense of breathlessness, reducing the welfare before slaughter. We investigated whether using hypercapnic-hypoxia (20% CO(2) and less than 2% O(2)) reduced aversion and discomfort compared to hypercapnia, and whether the quality of the stunning was adequate, meaning that no animals regain conscious after stunning. Moreover, we compared the impact of both stunning gases for meat and carcass quality. Our results suggest that both gases provoked aversion and discomfort, but these were lower in pigs stunned with the N(2) mixture compared to high CO(2). On the other hand, the stun quality of the N(2) mixture was poorer than high CO(2) stunning, given that more animals regained consciousness before sticking with the N(2) gas mixture. The stunning quality of the N(2) mixture, however, was improved when oxygen concentration was below 2%. Meat quality was slightly poorer in N(2) stunning compared to high CO(2), with a higher percentage of carcasses showing pale, soft, and exudative pork. ABSTRACT: This study assessed aversion, stunning effectiveness, and product quality of nitrogen and carbon dioxide (CO(2)) mixtures used for stunning pigs. A total of 1852 slaughter pigs divided into two similar batches was assessed during routine slaughter in a Swedish commercial abattoir using either hypercapnic-hypoxia (20% CO(2) and less than 2% O(2); 20C2O) or hypercapnia (90% CO(2); 90C) gas mixtures. Behavioral indicators of aversion and discomfort were recorded. After exposure, the stunning quality was assessed through brainstem reflexes. After slaughter, the pH and electric conductivity of carcasses were assessed to estimate the incidence of pale, soft, and exudative (PSE) pork, and the presence of ecchymosis were inspected. Compared to 90C, pigs exposed to 20C2O showed a later (p < 0.05) onset of behaviors indicative of aversion, and a lower (p < 0.01) incidence of breathlessness. However, unconsciousness (i.e., losing posture) appeared earlier (p < 0.01) in 90C compared to 20C2O. In 90C, all (100%) pigs were adequately stunned, whereas in 20C2O a 7.4% of pigs showed signs of poor stunning, especially when oxygen concentrations were >2% (p < 0.001). The percentage of PSE carcasses was higher (p < 0.01) in 20C2O than 90C. In conclusion, compared to 90C, 20C2O reduced aversion and discomfort but showed lower stun effectiveness, especially when O(2) was above 2%, and a slightly poorer pork quality.