Animal Welfare and Meat Quality Assessment in Gas Stunning during Commercial Slaughter of Pigs Using Hypercapnic-Hypoxia (20% CO2 2% O2) Compared to Acute Hypercapnia (90% CO2 in Air)

Abstract

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 (CO2)). However, it produces irritation of the mucosa and a sense of breathlessness, reducing the welfare before slaughter. We investigated whether using hypercapnic-hypoxia (20% CO2 and less than 2% O2) 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 N2 mixture compared to high CO2. On the other hand, the stun quality of the N2 mixture was poorer than high CO2 stunning, given that more animals regained consciousness before sticking with the N2 gas mixture. The stunning quality of the N2 mixture, however, was improved when oxygen concentration was below 2%. Meat quality was slightly poorer in N2 stunning compared to high CO2, with a higher percentage of carcasses showing pale, soft, and exudative pork.