Date Full Report Received


Date Abstract Report Received



Primary Investigator:
Humane euthanasia of sick or injured pigs raised in a commercial production facility is necessary when veterinary medical care and economic considerations deem that the animal cannot be rehabilitated. Several methods of euthanasia (i.e. injection of barbituric acid derivatives or pentobarbital, inhalation of gasses such as isoflurane or carbon dioxide (CO2), cervical dislocation, decapitation, captive bolt, and electrocution) have been approved by the American Veterinary Medical Association. However, these methods are difficult to implement (in a practical sense) in a commercial swine production facility due to the dangers of accidental human exposure (i.e. barbituric acid derivatives, pentobarbital, isoflurane, and CO2), the inability to physically perform cervical dislocation or decapitation appropriately, or the human dangers of performing captive bolt or electrocution methods of euthanasia. Most importantly, the humaneness of CO2 is being increasingly challenged, as it causes death through suffocation. Furthermore, these methods can be distressful to animal care takers and with barbituric acid derivative administration, limit the ability of the animal to be rendered into a useful product as well as generate concern if the carcasses of these animals are disposed of in landfills.

Humane euthanasia in a hypobaric chamber will allow swine producers to euthanize animal’s on-farm in a manner that may be less stressful to the animal, consistent, and acceptable to the public, and less stressful for workers. It furthermore shows promise as a humane stunning method for slaughter, since the point is to produce hypoxia without asphyxia.
Based on previous research conducted at Colorado State University (MacGregor, et al., 2008), the vision of the investigators for this experiment was to examine the efficacy of an on-farm hypobaric chamber that delivers the most effective and humane form of on-farm euthanasia. Three experiments were conducted utilizing seventy nursery weight pigs. Twelve pigs were euthanized prior to the main experiment to establish appropriate ascension parameters for the main experiment.

In the main experiment (Exp 3), fifty eight nursery weight pigs (5.6 ± 1.3 kg) were euthanized; twenty-six pigs were euthanized via hypobaric hypoxia (HH; approximate ascension of 36.9 m/sec) and thirty-two via CO2 gas induction at 20% the volume of the chamber per minute. Pigs were categorized into two health categories: healthy or moribund, and euthanized two at a time for each method by health category treatment. The trial was conducted at a commercial swine facility near Manhattan, KS, over three days in early October 2010. On the first day of euthanasia, some difficulty adjusting the chamber to sea level was experienced and 10 pigs in the hypobaric hypoxia treatment group were euthanized via CO2 after being at altitude for 20 minutes. Electroencephalogram (EEG) and electrocardiogram (ECG) data for these pigs was not included in this analysis. Approximately 24 hours prior to euthanasia, blood samples were collected from piglets for cortisol, lactate, epinephrine, norepinephrine and blood gas analyses. During euthanasia, one pig was restrained in a sling (similar to one developed by Panepinto, 1983) and equipped with an EEG and ECG recording device while the other pig was free to move about on the floor of the chamber. During euthanasia, behavioral data was collected. After death was confirmed, a blood sample was drawn from both piglets. Necropsies were performed to evaluate the presence of gross lesions on the brain, heart, lungs, trachea, oral cavity, integument, shoulder/hip/stifle joints, thoracic cavity, esophagus, diaphragm, liver, spleen, pancreas, stomach, umbilicus, urinary bladder, urachus, kidneys, ureters, stomach, small intestine, large intestine, cecum, mesentery, reproductive organs, and mesenteric lymph nodes.

Results of this experiment provide insight as to the specific biological and physiological changes that occur during CO2 and HH euthanasia methods. However, these data provide insight as to the specific biological and physiological changes that occur during euthanasia. Electroencephalogram data indicated that pigs euthanized via CO2 reached a complete isoelectric state faster than pigs euthanized via HH indicating a more rapid death. However, pigs euthanized via CO2 gasped more but had less bouts of paddling than pigs euthanized via HH. Furthermore, post-euthanasia percent hematocrit, hemoglobin and lactate concentrations, and pH were higher but pCO₂ was lower in HH compared to CO2 euthanized pigs. A higher blood pCO₂ coupled with higher incidents of gasping indicates that CO₂ euthanized pigs may have experienced a greater amount of asphyxiation prior to death. However, pigs euthanized via hypobaric hypoxia had more lung lesions and HH was not effective in euthanizing every piglet which raises questions about its effectiveness as a consistent method of euthanasia. Further research utilizing HH at different altitudes and CO2 at different induction rates may provide a more concrete solution to determining a low stress, humane method of on-farm euthanasia.

Contact Information:
Terry E. Engle Ph.D., Associate Professor/Ruminant Nutrition
Department of Animal Sciences
Colorado State University
208A Animal Sciences
1171 Campus Delivery
Fort Collins, CO 80523-1171