Effect of different carbon dioxide concentrations and exposure times in stunning of slaughter pigs: Impact on animal welfare and meat quality

The objective of this study was to determine the impact of different slaughter procedures on animal welfare and meat quality. Before slaughter in a dip-lift, one-gondola system, 460 pigs were exposed to an atmosphere containing either 80% or 90% CO2 for 70 or 100 s, and at the longer exposure time with stun-to-stick intervals of either 25–35 or 40–50 s. Clinical parameters (reflexes, catecholamines and lactate) showed deficiencies in animal welfare after stunning with 80% CO2 for 70 and 100 s, with an interval of 40–50 s, and with 90% CO2 for 70 s. Stunning with 80% CO2 for 70 or 100 s always induced stress, as indicated by higher lactate levels, and reduced meat quality as indicated by low pH24 values (5.4 in Musculus longissimus and 5.5 in Musculus semimembranosus) and low impedance (Py24) values, especially in combination with the longer stun-to-stick interval (40–50 s). Stunning with 80% or 90% CO2 in a dip-lift system was found to be acceptable for animal welfare (percentage of clinical reflexes) only in combination with the longer exposure time of 100 s and the shorter stun-to-stick times of 25–35 s. When 90% CO2 was used, the longer stun-to-stick interval of 40–50 s also gave results acceptable with regard to animal welfare. Generally, in comparison to 80% CO2 stunning meat quality was superior (higher pH24 and Py24 values) after stunning with 90% CO2.