Comparison of CO2 versus mixed CO2:Argon Gas at Different Flow Rates Using the Smart Box Euthanasia Device as an Effective Method of Piglet Euthanasia

A.S. Leaflet R2825
Larry J. Sadler, Graduate Research Assistant,
Department of Biomedical Sciences; Chad D. Hagen, Senior Vice President, Value-Added Science and Technologies, LLC; Chong Wang, Professor, Department of Veterinarian Diagnostic and Production Animal Medicine and Department of Statistics, Iowa State University;Tina Widowski, Professor, Department of Animal and Poultry Science, University of
Guelph, CA; Anna K. Johnson, Associate Professor, Department of Animal Science, Iowa State University;Suzanne T. Millman, Associate Professor, Department of Veterinarian Diagnostic and Production Animal Medicine, Iowa State University

Summary and Implications
The objective of this study was to compare the effectiveness and response of weaned piglets to 100% CO2 gas relative to a 50:50 CO2:Argon gas mixture as an effective tool for euthanasia. A total of 180 piglets, BW 4.6 ± 0.7 kg, were utilized. Piglets were 16 to 24 days of age.Two gas mixtures (100% CO2 and 50:50 CO2:Argon) and 4 flow rates (slow, medium, fast, and prefill; 20%, 35%, 50%, and prefill with 20%, chamber volume per minute, respectively) were examined. Two piglets were placed in a modified Smartbox™ (Euthanex Corp, Palmer, PA)chamber, in which the lid and one side are composed of clear plastic to facilitate behavior observations. Piglets were scored using direct observation for latency to perform threebehaviors associated with insensibility: loss of posture, last movement and gasping. Open mouth breathing occurred prior to insensibility and was used as an indicator of distress. The CO2:Argon gas mixture and slow flow ratesprolonged the duration of insensibility, as measured by last movement and did not confer advantages for measures of distress.

Introduction
The U.S. swine industry euthanizes piglets when their chances of survival are low and they are suffering due to injury or illness. This results in million of piglets being euthanized annually, and tools are needed to accomplish euthanasia quickly, economically and safely, as a repeatable humane process.

Carbon Dioxide (CO2) gas to euthanize young pigs is acceptable by National Pork Board guidelines and is increasingly common. CO2 is economical, relatively safe and readily available. CO2 is a colorless, odorless gas,which stuns by lowering the pH of the central nervous system. It is capable of doing this because it is mildly acidic. However, this acidity may cause sensation and distress. Argon has been proposed as a more humane alternative, since it is unreactive throughout the body’s systems, stuning through asphyxiation. Evidence from other species suggests that argon may be less aversive than the standard CO2 methods. Furthermore, little empirical research exists to support best management practices for onfarm CO2 euthanasia, in terms of gas flow rate, concentration or duration of exposure. Therefore the objective of this study was to compare the effectiveness and
response of weaned piglets to 100% CO2 gas relative to a 50:50 CO2:Argon gas mixture as an effective tool for euthanizing.

Materials and Methods
The protocol for this experiment was approved by the Iowa State University Institutional Animal Care and Use Committee (11-09-6825-S). The experiment was conducted from May to September, 2010.

Animals and housing: A total of 180 mixed sex piglets (90 barrows and 90 gilts) were used from commercial PIC genetic lines. Piglets were obtained and housed at the Iowa
State University Swine Nutrition Farm. Piglets weighed 4.6 ± 0.7 kg and were 16 to 24 days of age.

Experimental design: Piglets were compared as mixed sex pairs. The experimental design for this study was a 2 × 4 factorial arrangement of treatments. Two gas mixtures; 100% CO2 (CO2) and 50:50 CO2:Argon (CA) with fourdifferent chamber exchange rates: slow, medium and fast,allowing 20%, 35%, 50% chamber volume turnover per minute respectively, and pre-fill of the chamber with 20% chamber volume turnover per minute.

Euthanasia protocol: Piglets were placed into a plastic chamber (inside dimensions 43 wide, x 60 long, x 30 height, cm), with 2 clear sides facilitating behavior observations. The floor was fitted with a black rubber mat to prevent slipping. Gas was supplied utilizing a Euthanex AgPro™ (V-ast, Mason City, IA; Figure 1) and a constant gas flow
was provided by a compressed gas regulator (Western Enterprises, Westlake, OH). Between each treatment the chamber was blown out with ambient air.

Statistical analysis: Analysis was performed in SAS. OMB, GASP, and LP were analyzed as Univariate productlimit estimation of the survival curves. LM data was log
transformed and analyzed as a mixed model with fixed effects of sex and treatment, and blocked by day of
treatment. Raw means were calculated using Proc Means.

Results and Discussion
When comparing gas types, differences were observed for LM with CA treatment taking longer relative to CO2.Differences were not observed for OMB, LP or GASP between the two gas types. Within gas types, as expected, gas flow rate significantly (P < 0.001) affected LM, with theslow flow rate taking longer than the medium, fast, or prefill. No differences were observed for all other reported measures. In conclusion, CA and slow flow rate prolonged the duration of insensibility, as measured by LM and did not confer advantages for measures of distress (OMB).

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Source: Iowa State University Animal Industry Report 2013