Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Infectious Laryngotracheitis Outbreak in Saskatchewan Sandra Stephens Western College of Veterinary Medicine University of Saskatchewan
In December 1995, the Department of Agriculture and Food for the Province of Saskatchewan ordered the depopulation of a flock of laying hens infected with a virulent strain of the herpes virus causing infectious laryngotracheitis (ILT). As the province has no group of individuals in place to deal with such undertakings, the Director of the Provincial Diagnostic Laboratory and the Poultry Extension Veterinarian from the University of Saskatchewan were appointed as inspectors under the Diseases of Animals Act to organize and oversee the depopulation. 1. Quarantine: At the time the Depopulation Order was made, a notice of Quarantine was delivered to the infected premise. The quarantine was in reality an intensification of biosecurity; limited resources – people and monetary – make the feasibility of imposing a true quarantine impossible. The premise was posted, a barrier (gate) installed and the owner instructed on what precautions need to be taken by himself. All traffic to and from the farm was requested to use a specified route that did not pass by other poultry production units; all vehicles leaving the premise had the tires and wheel wells sprayed with a disinfectant solution. The cooperation of the owner was extremely important in this matter. These measures would likely not be adequate in a situation where the farm was not as isolated as this one was from other commercial operations. 2. Destruction: The mass depopulation of commercial poultry operations has been necessitated from time to time to disease outbreaks in a flock or chemical adulteration of a flock through the feed, therefore, a number of published reports dealing with the techniques employed for this purpose. The technique we employed was based on information in these published reports and on personal communication with people who had first hand knowledge of a large scale depopulation. The following factors were considered in developing the technique to be used in our situation: The technique must be:
Euthanasia Agent: The use of CO2 gas had been reported in many instances to give good results in the mass euthanasia of poultry. CO2 gas has historically been considered a humane method of euthanasia; it is readily available, inexpensive and does not pose a health risk to those using it if used in a well ventilated area (CO2 is heavier than air, therefore any gas that escapes from the gas chamber will settle close to the ground). Method: In a number of reports the birds were euthanized in the barn after confining them into a small area of the barn and sealing off the area. This method could not be used in our situation, as these were caged layers. It was questionable that we would be able to seal the entire building adequately to ensure concentrations of the gas in the cages were high enough to result in euthanasia. Also, when considering the time it would take to remove this number of carcasses from the cages, it was felt there would be problems with carcasses swelling due to heat or with rigor mortis. (We were subsequently told that killing the birds in the cages would have been disastrous; others had tired this and literally had to dismantle the cages to remove birds). Another method that has been used was to load the birds directly into a sealed semi-trailer that was filled with CO2. This method posed some questions as to the humane handling of the birds, as well it would also have required people to work outside for extended periods of time – the frigid winter temperatures made this a less desirable option. A smaller version of the "semi-trailer gas chamber" was used in our situation. Six metal containers 1m wide x 1m high x 1.5m long, on wheels were obtained from the local rendering company. These containers were easily converted into mobile "gas chambers". A layer of heavy plastic was secured to the top of each bin leaving a narrow opening at one end through which to put the birds and a ‘sliding’ plywood lid placed on top. The containers were then placed just outside the doorway to the barn. A hose carrying CO2 gas was run under the plastic at each end of the container so that it extended no more than 15 cm. below the lid. The gas was initially run in at 6-8 l/min, however, the CO2 regulators soon became frosted over and the accuracy of the flow rate questionable (the CO2 tanks were kept inside the barn to prevent the regulators from freezing up). Flow rates were therefore adjusted based on how quickly the birds were rendered unconscious (30-40 seconds). When each tank was full it was covered completely with the plastic and wood cover and let sit for 5 minutes to ensure the last birds added to the tank had died before emptying it. These containers are designed to be emptied into a semi trailer dumpster in a manner similar to the way in which garbage collection trucks operate. This meant that the carcasses would have no contact with the ground outside the barns, unfortunately the minus 35C weather took its toll on the equipment after the first day. On subsequent days the carcasses had to be dumped out of the containers, loaded into a front end loader bucket then put into the semi trailer. 3. Disposal: The accepted methods of disposal outlined in the Foreign Animal Disease Manual used by Agriculture and Agri-Food Canada in order of preference are: burial on site; burial off site, fermenting, rendering, burning, composting. Burial, burning and composting were not options for us in this situation. It was winter, with temperatures hovering in the –35C range, therefore the cost of having a pit dug was prohibitive. Furthermore, this farm is located in a prime "acreage" development area and had already been subjected to investigations regarding pollution of ground water and air quality. Government regulations involving environmental concerns were to dictate what method of disposal would be available to us; burial and burning would not have been allowed even if the weather had permitted it. The fact that we would not be able to dispose of the carcasses on site meant that we would have to transport them to another site. The nearest commercial poultry operation to this premise was 2.5km away and following the route we had previously set out for the quarantine would keep us 7-8km away from other commercial units. The local rendering plant agreed to transport and render the carcasses. The semi-trailer available to us did not have a cover; therefore the carcasses were allowed to freeze over night and transported after the top layer was frozen. Flying feathers and debris were not a problem. The environmental issues surrounding this particular farm combined with the extreme weather conditions resulted in the disposal of the liquid manure being the most challenging issue we had to deal with. The manure is stored in a covered cement pit, the contents of which are spread on adjacent land two or three times a year. The manure could not be left in the pit as it would freeze once the barns were empty, thus making the pit unusable until it thawed the following summer; it couldn’t be spread as the equipment would not work in the extreme cold and environmental regulations prohibited putting it in an earth pit. A concession was made by the environment people – the manure was super chlorinated and stored in a pit on the farm until it could be spread. Miscellaneous Considerations: Prior to proceeding with the destruction of the flock, it was necessary to determine how the building would be heated once the birds were removed. These barns do not have supplemental heat; therefore once the birds started to be removed, the temperature would start to drop. To prevent the building and liquid manure pit from freezing up, propane heaters used for heat in construction sites were installed. The temperature of the barns was important in facilitating cleaning and disinfection as well as in decreasing the likelihood of any virus surviving. (The virus is not as stable at warm temperatures, as it is in the cold). A major problem to be dealt with was manpower. We based loadout time on how long it took an experienced crew to empty a barn of spent hens. Due to the infectious nature of the disease, the regular loading crews in the area could not be used – time was added in to account for inexperience. We did not however account for fatigue factors and a high attrition rate. |
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