Date Full Report Received02/14/2011
Date Abstract Report Received02/14/2011
InvestigationInstitution: AgResearch, Hamilton, New Zealand
Primary Investigator: Mhairi Sutherland
Funded ByNational Pork Board
There are times on a swine farm when pigs become ill or injured, and the animal care person must decide if euthanasia is necessary, and if so what method of euthanasia is most humane for the pig, while alleviating worker stress. Blunt force trauma to the head is currently the most commonly employed method of on-farm euthanasia of pre-weaned piglets. When performed correctly, loss of consciousness is immediate, but the potential for delivery of sub-lethal blows, along with aesthetic unacceptability to many operators, has lead to the need for alternative methods to be developed. In contrast, gaseous methods of euthanasia, although requiring the use of specialized equipment in the form of a chamber and gas delivery system, may be both more reliable and less disturbing for the personnel involved and may therefore be a preferable method for on-farm euthanasia if managed well. Gas euthanasia has the additional advantage of not requiring the animal to be restrained by an additional person. Several gases are currently used to euthanize animals, such as rodents and poultry, including argon (Ar), nitrogen (N2) and carbon dioxide (CO2). However, animals exposed to CO2 may display behavioral and/or physiological signs of distress in response to CO2 inhalation. Using other gases, such as Ar or N2, either alone or in combination with CO2 appears to be preferable to CO2 alone, as gauged by measures of animal well-being. The other advantage to using Ar or N2 is that they are inert, non-flammable and non-explosive gases, making them practical choices from a work safety stand point. Few studies have been conducted evaluating the effectiveness of these gases (Ar or N2) as a means of on-farm euthanasia in young pigs, therefore the objective of this study was to evaluate different gases and gas mixtures (CO2, Ar and N2) as a humane method for euthanasia of young suckling pigs. In experiment 1, piglets received one of five gas treatments: 100% carbon dioxide (CO2), 90% argon in air (Ar), 90% nitrogen in air (N2), a mixture of 30% carbon dioxide/60% argon in air (Ar/CO2) or a mixture of 40% carbon dioxide/50% nitrogen in air (N2/CO2). In experiment 2 and 3, piglets received one of three gas treatments: 100% carbon dioxide (CO2), 100% argon (Ar), or a mixture of 40% carbon dioxide/60% argon (Ar/CO2). On each occasion a chamber was filled with the test gas and a piglet was placed inside. Throughout the experimental period, behavioral (e.g. escape attempts, vocalizations, loss of coordination, respiratory effort, convulsions) and physiological (e.g. brain activity as measured by electroencephalogram (EEG), cardiac activity as measured by electrocardiogram (ECG) and respiratory rate) data were continuously recorded until death. In addition, plasma cortisol and adrenaline levels (common markers of stress in pigs) were determined before treatment and immediately following death. A welfare index was established to assess the relative welfare compromise induced by each gas treatment. The index included five behavioral measures observed in the period prior to apparent loss of consciousness, beyond which there was no further potential for welfare compromise. These measures were: latency to onset of convulsions, duration of escape behavior, duration of increased respiratory effort, respiratory effort grade and duration of squealing. In experiment 1, four of the five gas treatments evaluated (Ar, CO2/Ar, N2 and CO2/N2) contained 10% air and therefore 2.1% residual oxygen. The duration of labored breathing, indicative of respiratory distress, was greater in those treatments containing residual oxygen. Additionally, animals in three of the residual oxygen treatments exhibited conscious behavior after the initial onset of convulsions, representing potentially serious welfare compromise due to distress or injury sustained during convulsions. Based upon the latency to respiratory arrest in each treatment, it appears that the inclusion of residual oxygen may prolong the survival time of piglets when exposed to lethal amounts of Ar or N2, without any apparent welfare benefit. It was thus decided to exclude residual oxygen from the gas treatments evaluated in the subsequent experiments the following three gas treatments were selected for further evaluation: 100% CO2, 100% Ar and 40% CO2/60% Ar. In experiment 1 and 2, the sum of ranks for each animal across the 5 measures yielded a single score indicative of welfare compromise, with a lower score equating to less compromise. According to this index, CO2 induced greater welfare compromise than either Ar or Ar/CO2. Furthermore, epinephrine concentrations in response to euthanasia were lower in piglets exposed to Ar/CO2 as compared to Ar or CO2 alone. These results suggest that 100% CO2 may cause piglets’ distress prior to loss of consciousness. Although Ar and the Ar/CO2 mixture did not significantly differ in terms of welfare impact, times to loss of consciousness, isoelectric EEG and respiratory arrest were shorter with Ar/CO2 than Ar, making this potentially more useful from a practical standpoint. However, the degree of welfare compromise observed in all treatments suggests that other alternatives to manually applied blunt trauma should be investigated.