Recovery of consciousness in hogs stunned with CO2: Physiological responses

• Stunning in CO2 chambers caused physiological disorders.
• Exsanguination should be performed immediately.
• Energy imbalance is aggravated if the animals recover consciousness.

The objective of the present study was to determine the impact of recovering consciousness on physiological responses in hogs stunned with different concentrations of CO2. A total of 1336 pigs were moved into a CO2 anaesthesia chamber for 90 s. The remaining pigs were assigned to 3 groups according to the CO2 concentration used for stunning: 85, 90 or 95%. Each group was then further divided into 2 sub-groups: those exsanguinated during the first 60 s after leaving the chamber without recovering consciousness (WRC); and those exsanguinated after more than 60 s that recovered consciousness (RC). The blood pH of the RC pigs decreased below 7.08, but their blood levels of Ca2 + (> 1.59 mmol/L), glucose (> 159.79 mg/dL), and lactate (> 103.52 mg/dL) all increased when compared to reference values (RV) (P < 0.05). Therefore, a greater metabolic and energy imbalance occurs during exsanguination when pigs recover consciousness. In conclusion, exsanguination should be performed immediately upon the pigs leaving the CO2 chamber.