Evaluation of the diving reflex in response to water-based foam vs. carbon dioxide gas depopulation in White Pekin ducks
Date
2012
Authors
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Publisher
University of Delaware
Abstract
The mass depopulation of production birds is an effective means of controlling fast moving, highly infectious diseases such as avian influenza and virulent Newcastle disease. While water-based foam as a method of mass emergency depopulation was conditionally approved by the United States Department of Agriculture Animal and Plant Health Inspection Service in 2006, limited testing has been done with ducks (Anseriformes). Three experiments were performed to assess the physiological responses of Anseriformes to foam depopulation using White Pekin ducks as a model. Experiment 1 evaluated the difference in time to unconsciousness, motion cessation, brain death, altered terminal cardiac activity, duration of bradycardia, and onset of bradycardia to onset of unconsciousness between foam and CO2
gas for ducks aged 5-9 weeks. Experiment 2 evaluated the effects of non-terminal submersion in both flowing and standing water and water-based foam on heart rate and duration of bradycardia. Experiment 3 evaluated the effect of abolishing bradycardia on difference in time to unconsciousness, motion cessation, brain death, altered terminal cardiac activity, duration of bradycardia, and onset of bradycardia to onset of unconsciousness between the treatments foam, CO2 gas and foam with an atropine injection for ducks aged 8-14 weeks. Atropine sulfate was injected to prevent bradycardia by blocking acetylcholine at parasympathetic neuroeffector sites. Experiment 1 resulted in significantly faster times to all four physiological points for CO2 gas as opposed to foam. Duration of bradycardia and onset of bradycardia to
onset of unconsciousness was significantly longer for foam than CO2 gas. Experiment 2 determined that both flowing and standing water and foam resulted in a diving reflex that led to pronounced bradycardia. All ducks survived and remained conscious throughout the experiment. Experiment 3 determined that there was a significant correlation between duration of bradycardia and time to unconsciousness, motion cessation, brain death, and altered terminal cardiac activity. The time to unconsciousness, motion cessation, brain death, and altered terminal cardiac activity was significantly faster for the treatment foam with atropine injection as compared to foam. There was no significant difference between foam and CO2 gas for these physiological points except brain death, in which CO2 was significantly faster than foam and not significantly different from foam with atropine injection. The results of these three experiments show that bradycardia as a result of the diving reflex occurs as a result of submersion in foam, and that the duration of bradycardia has a significant impact on the time it takes White Pekin ducks to reach unconsciousness and death during foam depopulation. CO2 gas can also trigger bradycardia and in Experiment 3 resulted in similar time to unconsciousness and death as foam. It can therefore be concluded that both CO2 gas and water-based foam will trigger bradycardia when depopulating White Pekin ducks, and extra exposure time should be allowed to compensate for this salvific response.