Comparison of water based foam and inert gas emergency depopulation methods of turkeys
Date
2010
Authors
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Publisher
University of Delaware
Abstract
Current control strategies for avian influenza (AI) and other highly contagious poultry diseases include surveillance, quarantine, depopulation, disposal, and decontamination. Selection of the best method of emergency mass depopulation needs to maximize human health and safety while minimizing disease spread and animal welfare concerns. The method used must be compatible with species, age, housing type, and disposal options. Research has shown differences in gassing and foam depopulation procedures when comparing time to and consistency of time to brain death. An overall goal of this project was to find a way to evaluate the welfare of the poultry subjected to a depopulation treatment. During depopulation, the time to unconsciousness needs to be evaluated to determine when the birds are no longer aware of their surroundings or feeling any pain. This study consisted of two experiments to evaluate the efficacy of mass depopulation methods. Experiment 1 was conducted as a proof of concept for the use of the alpha/delta (A/D) ratio in evaluating the time to loss of consciousness in poultry. Experiment 2 was conducted to evaluate the effectiveness of two mass depopulation methods on turkeys. The methods that were tested were carbon dioxide (CO2) gassing and water based foam. In Experiment 1, the use of the alpha/delta ratio was evaluated as a method to analyze poultry time to unconsciousness using layer hens. Experiment 1 tested the use of the alpha/delta ratio under controlled anesthesia and the resulting unconsciousness. This study was done as a proof of concept for application to subsequent studies. The results of this study indicate that there is a consistent suppression pattern in the transition from consciousness to unconsciousness. The alpha/delta ratio was suppressed by the effects of the isoflurane as the bird began to lose consciousness. The layer hens were found to become unconscious an average of 278 seconds after the start of the treatment with a standard deviation of 113 seconds. This concept was then used to evaluate the time to loss of consciousness in turkeys during depopulation in Experiment 2. The purpose of Experiment 2 was to evaluate the efficacy of two different treatments used for depopulating market age turkeys. This experiment was conducted using a randomized block design with commercial male turkeys exposed to one of two randomly selected depopulation treatments; either 100% CO2 gas or water based foam with ambient air. The time to unconsciousness, terminal convulsions, brain death, and cardiac relaxation were recorded for each bird. The time to unconsciousness and brain death were evaluated using the EEG signals recorded from a wireless transmitter surgically implanted into the brain of the bird. Motion cessation was determined through analysis of data recorded from an accelerometer attached to the turkey's leg during depopulation. Cardiac relaxation was evaluated through analysis of the ECG data recorded via wired electrode pads attached to the wing and legs. Being able to determine the point of unconsciousness allows for better evaluation of the effectiveness of different depopulation methods. Critical times for physiological events were extracted from the EEG, ECG, and accelerometer data and were compiled in Excel and statistical analysis was performed using SAS. The data subsets were not normally distributed and thus a non-parametric statistical analysis was conducted on each data subset in SAS. A Wilcoxon Exact test was used to analyze the treatment-dependent data sets. All tests were conducted at the 5% (α = 0.05) significance level. There was a statistically significant difference in the time to brain death between the two methods. Water based foam was the fastest treatment with respect to brain death (μ = 190 sec). The CO2 gas was significantly slower (μ = 242 sec). Water based foam resulted in faster (μ = 64 sec) time to unconsciousness than CO2 gas (μ = 90 sec). The time to terminal convulsions of the birds showed that there was no statistically significant difference in the time to motion cessation for water based foam (μ= 166 sec) and CO2 gassing (μ= 174 sec). The time difference for cardiac relaxation for water based foam (μ=208 sec) and the CO2 gas (μ= 242 sec) are not statistically significant. The results of this experiment show that water based foam is more effective at causing brain death than the CO2 gas. Though not statistically significant, water based foam caused unconsciousness, cardiac relaxation and motion cessation faster than CO2 gas. The times to brain death and unconsciousness for water based foam were also more consistent, with less variation from the mean compared to CO2 gas. When comparing water based foam and CO2 gas, there are other qualitative advantages to the use of the water based foam including responder safety and emotional welfare as well as compatibility with carcass composting. This information may also play a role in how agencies such as the USDA and organizations such as AVMA evaluate water based foam for mass emergency depopulation of poultry.