Patent Publication Number: US-7717773-B2

Title: Poultry stunning system

Description:
PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 11/651,250, filed Jan. 9, 2007, incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to poultry handling systems and more particularly pertains to a new poultry stunning system for rendering poultry senseless in a humane manner and to facilitate preparation of the poultry for processing while minimizing the excitement of the birds, and for emptying the unconscious but live poultry from transport cages. 
     BACKGROUND 
     In the poultry processing industry, a number of methods have been devised for stunning (preferably without killing) live poultry prior to processing into various food products. While the previous methods such as electric shock stunning are substantially directed to performing this operation in an efficient manner, there has been a growing trend toward implementing more humane methods of euthanizing the birds, while still preserving the quality of the meat. One approach that has been used is the implementation of carbon dioxide (CO 2 ) and or other gasses to “stun”, or reduce the consciousness of, the poultry prior to slaughter. Ideally, carbon dioxide or other stunning gasses should be used in a manner that reduces or eliminates the consciousness of the birds while keeping them alive, as regulations require that poultry be bled out prior to processing. 
     However, to preserve the quality of the meat, the birds should be kept as calm as possible prior to the euthanization so to preclude excitement, increased heart rate, adrenaline release into the bloodstream, and/or other factors that can cause increased blood flow to the birds&#39; extremities. Should any of the foregoing occur, the quality of the resultant meat is likely to suffer, as it is widely held that unstressed animals produce more palatable meat with a better texture. Further, unstressed animals tend to hold less blood in their extremities, thereby allowing the poultry to bleed out more completely. Thus, the process and apparatus employed to stun and euthanize the poultry should cause as little disturbance as possible to the birds prior to and during the application of the stunning and euthanizing. 
     Moreover, the stunning process should cause the bird to become unconscious (e.g., by reducing the brain activity of the bird), which minimizes the excitability of the bird, while not stopping or reducing the function of the bird&#39;s heart, a situation which can make it difficult to drain most of the blood out of the body of the bird, especially the extremities. Further, the size and health condition of the poultry can greatly affect whether a given amount of exposure time or concentration of carbon dioxide or other gasses either stuns, kills, or merely stresses live poultry. 
     As noted above, CO 2  stunning is one method of incapacitating poultry prior to euthanizing. One example of a known CO 2  stunning systems is shown in U.S. Pat. No. 6,848,987 to Draft (hereinafter referred to as “the &#39;987 patent”). While this system relates to using CO 2  to stun birds prior to processing, the process used introduces stressors to the birds prior to and during the stunning process, which can lead to an increased heart rate in the birds and the aforementioned problems resulting from the increased heart rate. 
     For example, in the system of the &#39;987 patent, the cages are subjected to numerous movements that can cause physical jarring of the birds and audible noises about the birds, which can lead to unnecessary excitement of the birds. Specifically, the cages, which are typically transported in stacks of two or more cages, must be unstacked from each other prior to moving through the system and the stunning of the birds. Since the structure of the cages is analogous to a stack of drawers, the unstacking of the cages functions to remove the top or ceiling from the cages, and this change in environment may disorient or excite the birds. In addition, the apparatus of the &#39;987 patent primarily moves the cages in a horizontal direction, yet requires that the cages be lowered or moved downwardly into a gas chamber, a further change in the birds&#39; environment that can cause a disturbance among the birds, and providing an area where CO 2 , which is heavier than air, may accumulate at levels higher than anticipated. Further, the &#39;987 patent reports that the presence of humidity to a gas chamber utilizing carbon dioxide can lead to the production of carbonic acid, further stressing the poultry. 
     Further, as discussed above, a method or system for adjusting the levels of CO 2  to allow for differing poultry sizes and health conditions of the animals would be greatly appreciated. In addition, since the application of carbon dioxide to the birds tends to dry their throats and cause panic in the birds this side effect should be minimized as much as possible. 
     Therefore, a system for stunning poultry that reduces the stress to the animals, allows for controlled adjustment of the stunning levels depending upon the particular poultry being used, based upon the type of poultry, their size, and their health, without risking the killing of the poultry or stressing the poultry without properly rendering them unconscious would be greatly appreciated in the art. 
     SUMMARY 
     In view of the foregoing disadvantages inherent in the known types of poultry handling systems now present in the prior art, the present invention relates to poultry handling systems and more particularly pertains to a new poultry stunning system for rendering poultry senseless in a humane manner and to facilitate preparation of the poultry for processing while minimizing the excitement of the birds, and for emptying the poultry from transport cages. Further, the present invention provides a method for adjusting the stunning capacity between loads to allow for varying type, size, and health conditions of the animals that are incoming. 
     To attain this, the present invention generally comprises a system for stunning poultry located in cages. The system comprises a moving apparatus for moving the cages along a path having a beginning and an ending, and a multiple stage stunning apparatus for stunning poultry in the cages while the cages move along the path. The stunning apparatus includes at least two, and preferably three or more stages with each stage subjecting the poultry to a different concentration of a gas in air that progressively increases. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     One significant advantage of the present invention is the capability to stun the birds while still in the cages and without unduly disturbing the birds caused by, for example, removing the birds from the cages, for example, unstacking the cages and raising and lowering the cages between stunning stations while moving the cages. Further, another advantage of the invention is the progressive exposure of the birds to an, increasing, but controlled concentration of the gas that gradually stun the birds in a manner that does not kill the birds but keeps them passive for euthanization. The invention also includes features that reduce potential negative effects of the gas on the birds, such as the dry throat panic reaction. 
     Further advantages of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and objects of the invention will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
         FIG. 1  is a schematic diagram of a new poultry stunning system according to the present invention. 
         FIG. 2  is a schematic top view of one embodiment of a poultry stunning system according to the present invention. 
         FIG. 3  is a schematic side view of a cage loading station of the present invention. 
         FIG. 4  is a schematic perspective view of one of the stations of the stunning apparatus of the present invention. 
         FIG. 5  is a schematic sectional view of one of the stunning stations of the present invention taken along line A-A of  FIG. 4 . 
         FIG. 6  is a schematic sectional view of one of the stunning stations of the present invention taken along line B-B of  FIG. 4 . 
         FIG. 7  is a schematic sectional view of one of the stunning stations of the present invention taken along line C-C of  FIG. 4 . 
         FIG. 8  is a schematic sectional side view of a cage emptying station of the present invention looking toward the ending of the path, particularly illustrating the cages in the normal orientation. 
         FIG. 9  is a schematic sectional side view of the cage emptying station of the present invention looking toward the ending of the path, particularly illustrating the cages in the tipped orientation. 
         FIG. 10  is a schematic side view of the washing station of the present invention. 
         FIG. 11  is a front plan view of a control system according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION 
     The present application relates to a system for humanely stunning poultry such as turkeys prior to processing, and particularly to a method that allows high throughput while still allowing for adjustments to be made between loads to preclude the stunning from killing the animals. 
     I. Overview of the Stunning System 
     According to  FIG. 1 , a poultry stunning system  10  according to one embodiment of the present invention comprises a series of stations utilized to stun and unload poultry prior to euthanization and processing. In particular, poultry is generally delivered to a processing facility for intake by truck, with the poultry being brought in on large cages  2  (see  FIG. 2 ), described in further detail below. Once the poultry is delivered to the processing facility, with the poultry being delivered in multiple large cages  2  that are stacked on top of one another, and/or cages having multiple tiers, the cages containing the poultry are unloaded from the truck, and placed into poultry stunning system  10  where they will generally progress from conveyor loading station  109 , to first stunning station  110 . Once cage  2  progresses into first stunning station  3 , a specified amount of subduing gas (such as carbon dioxide (CO 2 )) is released into the chamber. Thereafter, the cage progresses to a second stunning station  112 , and then on to third stunning station  114 , and finally on to cage emptying station  115  where the stunned poultry is removed from the cage and sent on for further processing. Optionally, as shown in  FIG. 10 , a final cage washing station  142  may be placed after the cage emptying station to allow for automatic cleaning of the cage and return of the cage to the truck. It will be appreciated that the system may keep a cage in constant motion from the time the cage reaches conveyor loading station to the time it progresses through cage washing station  142 . However, according to one embodiment of the present application, poultry stunning system  10  causes a cage to stop at each stunning station for a specified period of time as further discussed below. 
     As will be appreciated, according to one embodiment of the present invention shown in  FIG. 2 , poultry stunning system  10  is preferably automated through the use of a conveyor system  20 , which allows a cage  2  to be loaded at loading station  109 , and then to be automatically conveyed through the remaining stations by an operator or computerized system which controls the timing at each station and allows for higher throughput with decreased stress in the poultry. It will be appreciated that system  10  as shown in  FIG. 2  is utilized to bring in live poultry, and thereafter routing the live poultry through system  10  to stun or lowering the consciousness level of live poultry, such as turkeys, to facilitate the handling of the poultry without placing undue stress on the birds. Thus, the stunning system  10  through its automated process of lowering the consciousness level of live poultry without removing them from cages reduces injury of the birds, and thus makes the handling of the birds easier to perform, even in handling high volumes of poultry. System  10  is thus highly suitable for use in the emptying of unconscious poultry from portable cages  2  that are used for transporting the poultry in a live condition between locations, such as between the facility in which the birds are raised and the facility at which the birds are processed into different food products. 
     In the illustrative embodiment shown in  FIG. 2-5 , the cages  2  that hold the birds are generally constructed of rectangular metal frame members with elongate confining elements (such as wire) disposed between the frame members that permits the free flow of air into and out of the interior of the cages while confining the birds within the cages. Preferably, but not necessarily, more than one of the cages may be vertically stacked together to form a plurality of tiers, each containing the birds to be processed, and be moved along the path  14  in a stacked set. Illustratively, three of the cages may be included in a set that is positioned in a stack on the conveyor in the same location. Advantageously, the cages are often transported on vehicles in vertical stacks of three, so the stacked configuration of the cages for movement in the system  10  does not have to be changed from the configuration of the cages in the previous transportation mode, thus lessening the disturbance the birds during movement from the transport vehicle to the system of the invention. 
     It will be appreciated that according to one embodiment of the present application, cages  2  may be designed such that a single cage  2  comprises what would normally be two or three cages, such that a single cage  2  comprises a single unitary cage that is a multiple tiered cage such as the three tiered cages. One example of cages that are suitable for use with the invention have three levels, with each level having a size of approximately four feet wide by approximately four to eight feet long by approximately 17 inches high, an cages utilizing three tiers (also termed “batteries”) may hold approximately 48 to 57 turkeys of about 38-42 pounds each. While use of multiple level cages has been generally avoided due to the difficulty in delivering similar concentrations of subduing gas to each level of such cages, the present stunning system  10  utilizes certain features that overcome these issues and thereby increases the throughput and productivity of stunning system  10  over previous systems. 
     It will be understood that the invention is not limited to usage with cages with the dimensions set forth above, and thus cages of other sizes or other multiple levels may be employed. Those of ordinary skill in the art will appreciate that the present system can be adapted to smaller sizes of poultry, and the present system is readily adaptable to embodiments in other animals, including beef and pork. For example, in an alternate embodiment, chicken cages having 5-6 tiers may be utilized, with each tier measuring about 4 feet by 4 feet by 17-18 inches. Such a set of cages (also known as a “battery”) typically holds approximately 90-120 chickens at 3-7 pounds per chicken. 
     In the illustrative embodiment, it is useful to orient the cages  2  so that the length dimension of the cages extends transverse to the longitudinal direction of movement of the cages through the system  10 , and the width dimension of the cages extends substantially parallel to the longitudinal direction of movement, but several other orientations can be used. 
     According to  FIG. 2 , stunning system  10  of the invention utilizes a conveyor  20  to move cages  2  along a path  14 . Path  14  has a beginning portion  16  and an ending portion  18 , but the length of beginning portion  16  and ending portion  18  can be adjusted to allow for additional stations such as cage washing station  142  shown in  FIG. 10  but not shown in the illustrative embodiment of  FIG. 2 . The path  14  may be linear or straight, or may be non-linear in character. The stunning system  10  may include a number of stunning stations located along the path  14  between the beginning portion  16  and the ending portion  18  of the path, preferably at least 2, and more preferably at least 3 stunning stations located in close proximity or adjoining one another. Additionally, other stations such as loading station  109  or emptying station  115  may be used as well. 
     II. The Conveyor System 
     As discussed above, stunning system  10  may utilize a conveyor system  20  for automatically moving cages  2  from the beginning portion  16  to the ending portion  18  of path  14 . As shown in  FIGS. 2 and 3 , the system  10  may comprise a conveyor system  20  for moving the cages along path  14 , and conveyor system  20  may extend between beginning portion  16  and ending portion  18 . Conveyor system  20  has an upper support plane  22  on which the cages are supported as the cages are moved by a conveyor element  24  along path  14 . In certain preferred embodiments of the invention, conveyor system  20  is relatively porous or open to gas flow to permit air and other gases to relatively freely pass through the upper support plane of the conveyor. Preferably, the vertical height of the conveyor  20  does not rise or lower significantly while it moves between the stunning stations, and thus cages moving along the conveyor do not make sudden or significant vertical movements that disturb the birds in the cages  2 . 
     Turning now to  FIG. 3 , conveyor system  20  may comprise one or more of conveyor elements  24  that extend in the direction from the beginning and ending of conveyor system  20 . Conveyor elements  24  may comprise a chain, chain links, belts, or other components used to urge an element forward on a given path. In addition, conveyor elements  24  may comprise a pick-up bar  32  located on conveyor element  24  and operable to engage the back of a cage  2  to urge cages  2  in a forward position as conveyor system  20  operates along path  14 . Optionally, conveyor elements  24  may be laterally spaced from each other to create gaps between the elements  24  through which air and gases can move. Conveyor elements  24  are movable in a longitudinal direction  26  of the conveyor system  20 , so that cages  2  rested on or urged by conveyor elements  24  are moved in the longitudinal direction of conveyor system  20 . In one embodiment, as shown in  FIG. 2 , the conveyor system  20  includes two conveyor elements  24 , with one element on a first lateral side of the conveyor system  20 , another conveyor element  24  on a second lateral side of the conveyor system  20 . Optionally, additional conveyor elements  24  may be used, as well as a guide fin  25  to help keep cages  2  on conveyor system  20 . Conveyor system  20  may be continuous between the beginning portion  16  and ending  18  of the path  14 , but may also include a plurality of longitudinally-extending conveyor segments extending along different longitudinal sections of the path. 
     According to one exemplary embodiment, conveyor elements  24  of conveyor  20  may move in a substantially continuous manner by operation of motor driven conveyor that engages with conveyor elements  24  by drive wheel  27 , or other means known in the art. However, conveyor elements  24  may move in a series of discrete, discontinuous movements, as cages  2  are moved through each station and the movement of the conveyor is paused to hold the cages in each station for a specified period of time. 
     As discussed above, and shown in  FIG. 3 , each longitudinally-extending conveyor element  24  of conveyor system  20  optionally comprises a belt or a chain made up of smaller links that is moved in a longitudinal direction of the conveyor along the path  14 . Conveyor elements  24  are thus flexible for forming contours in the path of the conveyor in the vertical direction. Conveyor system  20  may also comprise a pick up bar  32  mounted on the chain for engaging the bottom portions of cages  2  resting on the upper support plane  22  of the conveyor  20 . A pick-up bar  32  may be mounted on each of the chains at longitudinally-equivalent locations on the conveyor  20 , so that the pick-up bars of each of the chains are laterally abreast of each other as the chains are moved along the path. A plurality of the pick-up bars  32  may also be mounted on each of the chains at longitudinally-separated locations along the chain so that a number of the cages  2  may be simultaneously moved along by the conveyor at different longitudinal locations on the path  14 . For example, the pick up bars  32  may be spaced approximately six feet from each other along the chains to achieve a desired spacing between the approximately 4 foot wide cages of approximately 2 feet. Other spacings for other sizes of cages may be employed, and pick up bar  32  may comprise any raised surface on conveyor elements  24  operable to contact the back of cages  2 . 
     III. Loading a Stunning System 
     At the beginning  16  of the path  14 , the stunning system  10  may include a means for loading the cages onto the conveyor system  20  for movement along the path  14 . As shown in  FIGS. 2 and 3 , loading station  109  may thus be located at the beginning  16  of the path to permit cages  2  to be placed on the conveyor  20  in a manner that can accurately position the cages on the conveyor while also minimizing the disturbance to the birds in the cages. The loading station  109  may include a platform for resting the cages  2  upon, or a cage may be simply placed upon conveyor system  20 . Alternately, a fork truck may be used to load the cages onto the loading station. Once the conveyor  20  advances such that the cage moves along the path  14  and is no longer located above the loading platform, another cage may be placed on the platform. 
     IV. The Stunning Apparatus 
     A. General Progression Through the Apparatuses 
     Once cages  2  are loaded onto conveyor system  20 , the cages are advanced along the stations discussed in  FIG. 1 , and progress through system  10  as shown in  FIG. 2 . Each multi-stacked or tiered set of cages is advanced through multiple stunning stations (illustratively shown as three stunning stations  110 ,  112 , and  114 ) as shown in  FIG. 2 , allowing for progressive stunning to occur in an efficient manner. Turning now to  FIGS. 4-6 , each stunning station comprises an apparatus  56  for stunning or reducing the consciousness level of the birds in the cages  2  as the cages move along the path  14  on the conveyor system  20 . Significantly, the stunning apparatus  56  does not require that the birds be removed from the cages  2 , or that the cages be removed from the conveyor  20 , in order to stun the birds. 
     Turning now to  FIGS. 5 and 7 , each stunning apparatus  56  employs a subduing or stunning gas  13  introduced to chamber  64  via gas port  75  (see  FIGS. 5 and 7 ) to lower the consciousness of the birds, said stunning gas  13  being introduced into chamber  64  and circulated through stunning apparatus  56  approximately as shown by the dashed lines in  FIGS. 5-7 . Stunning apparatus  56  operates by creating a relatively higher concentration of stunning gas  13  within chamber  64  relative to outside air, causing the birds to breathe air mixed with the stunning gas  13 . In an exemplary embodiment, the stunning gas  13  is carbon dioxide, but optionally another gas having a similar consciousness-lowering effect on poultry may be used. For example, argon, nitrogen, and other relatively inert gasses may be utilized. Further, the stunning apparatus  56  preferably exposes the birds to progressively greater concentrations of the gas, in at least two, and preferably three stages, to minimize the distress of the birds, decrease the possibility of accidentally killing the birds during the stunning process, and to increase the throughput of the stunning system to allow for greater productivity. In the illustrative embodiment of the invention described herein, three stages with three different concentrations are employed as discussed in further detail below, but it will be appreciated that the invention may be implemented using a different number of stages with different stunning gas concentrations and/or exposure times. Alternately multiple cages may be included in each stunning apparatus  56  and spaced laterally along conveyor  20  by increasing the size of chamber  64  and conveyor  20  without substantially increasing the stunning gas concentration or stun times while thereby increasing size of chamber  56  and conveyor system  20 . 
     According to the exemplary embodiment in  FIG. 2 , each stage, or station, of the stunning system  10  comprises a stunning apparatus  56  that is optionally similar to the other stunning apparatuses  56 , and each stunning station is positioned along path  14 . Preferably, the first stunning station  110  receives first cages  2 , and vertically moveable doors on the first stunning station  110  (not shown) descend downwardly and close to form a reasonable gas seal (see  FIGS. 4 and 5 ) such that the subduing gas  13  can be released into the chamber  64  and maintained at a desired first concentration. Conveying system  20  stops, allowing the first cages  2  to remain in the first stunning station  110 . Subduing gas  13  is released into stunning station  110  until a first desired concentration of subduing gas is reached, and the poultry is exposed to the first desired concentration of subduing gas for a selected period of time. Thereafter, the doors on the first stunning apparatus  56  are opened, and conveying system  20  urges the first cages  2  into the second stunning station  112  and optionally urges a second cages  2  into the first stunning station  112 . 
     When first cages  2  are urged into second stunning apparatus  56 , the doors on the second stunning station  112  close and conveying system  20  stops, allowing the first cages  2  to remain in the second stunning station  112 . Subduing gas  13  of the same and/or different type is then released into the second stunning station  112  at a second desired concentration, and the poultry is allowed to remain therein for a selected period of time. Preferably, second cages  2  are subjected to first stage stunning at first station  110  while first set of cages  2  are undergoing second stunning in second station  112 . Optionally, fine droplets of water are dispersed within the second stunning station  112  to preclude the poultry from having a dry throat reaction, and causing them to remain calm. Thereafter, the doors on the second stunning apparatus  56  are opened, and conveying system  20  urges the first cages  2  into the third stunning station  114  and optionally urges the second cages  2  into the second stunning station  112  and a third cages  2  into the first stunning station  110 . 
     When first cages  2  are urged into third stunning station  114 , the doors on the third stunning station  114  close and conveying system  20  stops, allowing the first cages  2  to remain in the third stunning station  114 . Subduing gas  13  of the same and/or different type is then released into the third stunning station  114  at a third desired concentration, and the poultry is allowed to remain therein for a selected period of time. Preferably, second and third cages  2  are subjected to second and first stunning at stunning stations  112  and  110 , respectively, while first cages  2  are undergoing third stunning at third station  114 . In a preferred embodiment, the first selected concentration of the subduing gas  13  is lower than the second selected concentration of the subduing gas, which is in turn lower than the third selected concentration of the subduing gas. Further, any additional stations that are optionally arranged along the path are calibrated such that the birds in the cages are exposed to progressively greater concentrations of subduing gas  13  as they progress through the line. 
     B. Discussion of Details of Exemplary Embodiments of a Stunning Apparatus 
     Turning now to  FIGS. 4-7 , each of the stunning apparatuses  56  optionally comprise an apparatus  60  for mixing air and the subduing gas  13  and circulating the mixture through the cages as the cages move along the path  14  on the conveyor  20 , thereby infusing the air/gas mixture inside and about the cages  2  with a desired level of the subduing gas  13 . The mixing apparatus  60  offers advantages over the prior art, as it will be appreciated that injection of pure carbon dioxide will cause high concentrations of CO 2  to be present in certain areas of a stunning chamber while other areas remain at low levels of CO 2 , particularly because CO 2  is heavier than air. Because this “puddling effect” can cause some birds to be exposed to varying concentrations of CO 2 , some birds may be killed while others remain relatively unaffected. Such a system results in varying quality of resultant meat. Thus, apparatus  60  for mixing air and the subduing gas  13  is utilized in certain preferred embodiments of the present application. 
     As shown in  FIG. 4-7 , apparatus  60  for mixing air and the subduing gas  13  comprises a plenum structure  62  for adding the gas to the ambient air, producing a flow of the mixture of air and the gas, and guiding the flow of the mixture through the cages and in on path  14  while located within chamber  64 . The plenum  62  may extend about a portion or section of the conveyor  20 , and in some embodiments the plenum  62  encircles the conveyor, to achieve the desired infusion of the gas and air mixture into the cages. Turning now to  FIGS. 5-7 , stunning station  56  has an interior  64  that defines a chamber, and includes an inlet  66  and an outlet  68  that extends into the chamber  64 . The inlet  66  may be positioned below the path  14 , for intaking air from below the path, and the outlet  68  may be positioned above the path for outputting air above the path. The path  14  is positioned between the inlet  66  and the outlet  68  to create a flow of the gas and air across the path and through the conveyor  20 . 
     The plenum structure  62  thus has an outlet portion  70  positioned above the path  14  for handling the flow of the gas and air mixture as it exits the plenum, and an inlet portion  72  positioned below the path for handling the flow of the gas and air mixture entering the plenum. Plenum  62  is preferably supported by the side and top walls of chamber  64 . The end walls of chamber  64  define an entry opening  78  and an exit opening  80  through which conveyor  20  may move cages  2  into and out of chamber  64  when the doors are in the open position. 
     Further according to  FIGS. 5 and 7 , at least one, and preferably three stunning gas ports  75  are optionally present within the chamber, and are situated to direct stunning gas  13  at each of the three levels of multi-tiered cages  2  while apparatus  60  continues to mix the air and subduing gas  13  while gas  13  is being injected into chamber  64 . If carbon dioxide is used as a stunning or subduing gas  13 , carbon dioxide may be supplied by a modular carbon dioxide pressure build vaporizer such as those supplied by Carbo Tech, Inc. of Monroe, Ga. 
     Oxygen or other gas sensors  108  (see  FIG. 7 ) are optionally utilized to monitor concentrations of the subduing gas  13  within each stunning apparatus  56 . Use of oxygen sensors allows an operator to monitor the volume of oxygen being displaced by the volume of added or infused subduing gas or gasses. One can extrapolate the volume/concentration of the subduing gas from this oxygen measurement. For example, according to an illustrative embodiment of the present application, a first chamber  110  may be infused with sufficient stunning gas to ensure that the oxygen sensor within stunning station  110  reads between about 18-20% oxygen during the stunning portion of the cycle; a second chamber  112  may be infused with sufficient stunning gas to ensure that the oxygen sensor within stunning station  112  reads between about 12-14% oxygen during the stunning portion of the cycle; and third station  114  may be infused with sufficient stunning gas such that the oxygen sensor with in third stunning station  114  reads between about 3-4% oxygen. 
     It will be appreciated that stunning poultry of differing sizes will generally require the same concentration, by percent volume, of stunning gas for similar total masses of poultry. However, it will be appreciated by those in the art that different amounts of stunning gas will need to be added to the chamber to effect and sustain those concentrations. 
     According to one embodiment of the present invention, a heating mechanism is optionally used to heat subduing gas  13  prior to injection into the stunning apparatus. It will be appreciated that use of a heating mechanism allows for better mixture of the subduing gas  13  to a desired temperature, typically the ambient air temperature within chamber  64  of the stunning apparatus  56 , thereby allowing for a more homogenous mixture. In addition, having the stunning gas  13  heated just prior to injection prevents uncontrolled expansion of the subduing gas  13  after injection into the stunning apparatus  56 , which can cause inadvertent overdosing of the poultry. In addition, less total volume of subduing gas  13  need be used when the subduing gas is pre-heated. It will be appreciated that several different heating apparatuses can be used to heat the subduing gas  13  prior to injection, including a steam heater capable of heating and expanding the carbon dioxide just prior to injection. 
     As will be appreciated, maintaining a particular concentration of subduing gas  13  within the stunning apparatus  56  can be more efficiently accomplished when openings to the stunning apparatus  56  maintain a method for precluding the gas from escaping. The entry  78  and exit  80  openings of the stunning apparatus may be obstructed in some manner to reduce or block the escape of the gas/air mixture. In one embodiment of the invention, an air curtain generating apparatus may be employed to create a curtain of air moving across each of the entry and the exit of the chamber to facilitate the retention of the gas and air mixture in the interior. It has been found that use of a movable door, such as an overhead door with a seal material on its lower descending edge portion, is generally more effective in maintaining the subduing gas concentration within the stunning apparatus. 
     As shown in  FIGS. 4 and 7 , the stunning apparatus  56 , including chamber  64  and plenum  62  may include various access doors, such as an upper access door  84  and a lower access door  86  in the intermediate portion  74 , for allowing access to various portions of the interior  64  of the stunning apparatus  56 . The access doors may also be provided with transparent windows  88  to permit visual observation of the interior of the plenum, and thereby allowing an operator to observe the poultry during the stunning so that subduing gas  13  concentrations can be adjusted if the desired effect is not occurring. The plenum  62  may also have air inlet openings that permit fresh, filtered air to be added to the flow of the gas/air mixture moving through the interior of the plenum during evacuation of the air/gas mixture. The stunning apparatus  56  may also include a drain  94  to permit fluids to exit the plenum when the chamber  64  is cleaned. 
     As shown in  FIGS. 6 and 7 , mixing apparatus  60  may also include an air flow apparatus  96  for causing or inducing the flow of the gas and air through the chamber  64  and the plenum  62 . The air flow apparatus  60  may be mounted on the plenum  62 , and may be located in the chamber  64  of the plenum. The air flow apparatus  96  may be located in an intermediate portion of the plenum  62 . The air flow apparatus  96  may comprise at least one fan that is positioned in the interior of the plenum for moving the gas and air mixture through the chamber  64 , out of the outlet  68  and into the inlet  66 . Optionally, additional fans may be included. The air flow apparatus may include a wall or other barrier positioned in the interior of the plenum that blocks any movement of the gas and air mixture except through the fans. 
     As shown in  FIGS. 5 and 7 , the stunning chamber also comprises a gas port  75  for injecting stunning gas into the chamber. The gas port  75  may be positioned in chamber  64 , and may be positioned between the inlet  66  of the plenum and the air flow apparatus  96 . It will be recognized that the gas injector of port  75  is not limited to a single injector, and may include a plurality of gas injectors. Optionally, a gas port  75  is mounted in the top of chamber  64  and positioned with three separate injector nozzles to direct the subduing gas at each of the three tiers of cages  2  as shown in  FIG. 7 . 
     The stunning apparatus  56  may also include a gas sensor  108  for detecting a concentration of the subduing gas  13  in the flow of air and gas. The gas sensor  108  is positioned in the interior of the plenum  62 , and the gas sensor may be positioned between the outlet  68  of the plenum and the air flow apparatus  96 . Optionally, other sensors may also be provided for measuring various other characteristics of the flow through the plenum or inside chamber  64 , such as the concentration of oxygen (as O 2 ) in the mixture flow, and may be located within chamber  64 . 
     Turning now to  FIG. 2 , in the illustrative system utilizing three stunning apparatuses  56  as three separate stations (labeled  110 ,  112 , and  114  for clarity), the first station  110  of the system  10  produces a concentration of the gas in the total atmosphere between approximately 8 percent and approximately 19 percent concentration of carbon dioxide or other subduing gas  13  by volume. This level of carbon dioxide concentration in the gas/air mixture is effective to make the birds feel slightly tired, while the birds are being initially exposed to the flow of the gas/air mixture through the cages and the interior of the chamber of the stations. 
     Optionally, it has been found that the first and/or second stunning stations may include means for increasing the humidity in the interior of the stunning station  56  that functions to counteract any tendency of the increased carbon dioxide concentration to dry out the throats of the birds and cause discomfort to the birds discomfort which could lead to panic and distress. The increase in humidity may be accomplished by positioning a water spray assembly in the interior of the plenum  62  of the first station to create a light mist in the air. In one embodiment shown in  FIG. 5 , the humidity level is increased by one or more misting nozzles  116  that spray water or other humidity raising liquid into the gas/air mixture circulating through the first station  110 . The misting nozzles  116  may be located in the chamber, or in the air path outside of the chamber. Optionally, the misting nozzles may be located in other stations of system  10 . For example, injection of a pint of water into an approximately 5 foot by 5 foot by 10 foot chamber has been shown to be effective in reducing the dry throat panic reaction, with it being understood that the relative amounts of water can be adjusted in view of the relative humidity of the air. 
     The second station  112  of the system produces a concentration between approximately 34 percent and approximately 43 percent concentration of subduing gas by volume. This level of carbon dioxide concentration in the gas/air mixture is effective to make the birds lie down or sit down, with their heads still up, but with the birds on the edge of unconsciousness: 
     The third and final station  114  of the system produces a concentration between approximately 81 percent and 89 percent of subduing gas by volume. This level of carbon dioxide concentration in the gas/air mixture cause the brain of the birds to be inactive, but still allows the heart to continue pumping blood. 
     The period of time that the cages, and the birds in the cages, are exposed to the particular concentration of the gas may vary, and may be up to ten minutes or more to achieve the full effect of the raised gas concentration on the birds. Preferably, the time of exposure subduing gas is of a much shorter duration (i.e., approximately 30-70 seconds). This time of exposure may be achieved by stopping the movement of the conveyor  20  for the appropriate time period to keep the cages  2  in the respective station of the system, keeping the cages  2  in the respective station of a system between the inlet  78  and outlet  80  of the chamber  64  of the station. In some preferred embodiments of the invention, the conveyor  20  operates on a series of equal time length cycles that includes the time that the conveyor is moving and time that the conveyor is stationary between the movements. In the illustrative three stage embodiment invention for turkeys of about 38-42 pounds each, each cycle lasts for approximately 73 to 82 seconds, with the conveyor moving for approximately 28-30 seconds, and remaining substantially stationary for approximately 45-52 seconds-during which time stunning gas is introduced and stunning occurs. It will be apparent that the cycle times could be longer or shorter, and may be unequal in length of time. For example, in an illustrative two stage stunner, a time of 54 to 66 seconds could be used during the stunning portion of the cycle, with concentrations of stunning gas remaining similar to the second and third stations used in the three stage system example. However, concentrations of the gas must be adjusted to allow for the accumulated effect of the gas for differing time periods. It has been observed that using the stunning method and apparatus as described herein results in significantly improved meat quality, including less blood spotting and reduced ruptured blood vessels and wing breakage. 
     It will be appreciated that the use of stunning apparatuses  56  that are elevated above the floor of the processing facility, and those that utilize an air mixing plenum  62  provide a means for precluding carbon dioxide from accumulating within the bottom of the stunning apparatus  56  to a level that is detrimental to the poultry. 
     In one embodiment of the invention, each of the stations  110 ,  112 ,  114  is configured to hold one set of 3 tiered cages  2  described above on the conveyor at a time, so that the birds are exposed to the environments in the plenums of each of the stations for approximately equal time periods. Optionally, but less preferably, one or more of the stations may accept more than one set of cages on the conveyor, and in one embodiment, the first and second stations hold one set of cages each and the third station holds two sets of cages. 
     The chambers of stations  110 ,  112 ,  114  may be positioned closely adjacent to each other, even close enough that there is no appreciable gap or space between the stations, but the stations may be spaced or separated from each other along that path. When the stations are positioned closely adjacent to each other, the entries and exits of the respective stations may be aligned with each other, and optionally, a sealing structure may be used to surround and connect opening  78  and  80  of adjacent stations to effect a substantial gas sealed passage between the stations. Optionally, the second station  112  may be equipped with an evacuation apparatus (not shown) that is capable of quickly evacuating or pulling the gas and air mixture from the plenums and/or the chambers of the stations. The evacuation apparatus pulls the gas and air mixture out of the interior of the second station  112 , which in turn pulls the gas and air mixture present in each of first  110  and third  114  stations into the interior of the second station. In turn, air is drawn into the entry opening  76  and exit  80  of the first station  110  and the exit opening of the third station  114 , thus flushing the gas and air mixture from the chambers and replacing it with environmental air. The removal of the residual gas by an evacuation apparatus from the plenums of the stations  110 ,  112 ,  114  permits personnel to access the interiors of the plenums without exposure to the increased concentrations of the gas. Also, the quick removal of the gas and air mixture from the plenums of the stations can increase the likelihood that the birds located in the stations when the movement of the conveyor is stopped can be removed from the influence of the gas, thus increasing the likelihood that the poultry will not be killed by overexposure to the gas and thus may be preserved alive. 
     C. The Control System 
     In order to automate and control the stunning system  10  as well as the gas concentrations, according to one embodiment of the present application, a control system  200  allows an operator to adjust the subduing gas  13  concentrations within each stunning apparatus  56 , as well as control the speed of conveyor system  20 , the opening and closing of the chamber doors, and monitoring the atmosphere within each chamber  64 . 
     According to one embodiment shown in  FIG. 11 , control system  200  provides a control screen  210  for displaying a graphic user interface between the subduing gas storage, conveyor system  20 , circulation fans within the chamber  64 , the temperature of the subduing gas, and gas injection ports  75 . Further, control system  200  includes manual adjustment knobs and mechanisms for each of the controls, in the event that the computerized processor within control system  200  malfunctions. A screen shot of the control system  200  provides for automated control of each of these controls, allowing stunning system  10  to run as programmed. In addition, a screen shot wherein the percentage of subduing gas  13  is set for each stunning station, as well as the amount of time that cages  2  are to be exposed to the percentage of subduing gas  13  may be shown. In addition, an oxygen sensor may be used to determine the amount of oxygen that has been displaced by subduing gas  13 , with the oxygen percentage being displayed on control screen  210 . Further, as can be seen, sensors may be used in the working floor of the production facility to monitor carbon dioxide levels within the facility to ensure that safe levels are maintained for any workers on the production floor. The levels sensed by these sensors can be displayed on control screen  210 . 
     It will be appreciated that control system  200  allows an operator to adjust the amount of subduing gas  13  to a percentage within the range described above such that the operator can allow for differences in the weight of the birds delivered, the health of the birds delivered, the temperature, and the humidity of the environment. Since each load of birds may have varying size and health, such adjustment is desirable according to one embodiment of the present application, as an appropriate amount of subduing gas for one load may kill another load of birds. In addition, an appropriate amount of subduing gas  13  for another load of birds may not adequately affect a third load of birds. As such, the optional viewing portals each stunning apparatus  56  and a camera  156  as illustrated in  FIG. 9  can be used to allow for adjustability of the system  10  as it is being used. 
     Additionally, it will be appreciated that control system  200  optionally utilizes a sensor within each stunning apparatus  56  to determine whether a cage is present. If a cage is not present, no subduing gas  13  is injected into the stunning apparatus. By utilizing such a sensor, subduing gas  13  is not unduly wasted, and there is less chance of increased levels of the subduing gas  13  within the working floor of the production facility. 
     IV. Post-Stunning Processes 
     According to one embodiment of the present application, after cages  2  have progressed through the three stunning stations  110 ,  112 , and  114 , the cages further progress to cage emptying station  115 , and are emptied so that the inactive, but live poultry can be euthanized or dispatched. As shown in  FIGS. 8 and 9 , to assist with the emptying of the cages  2 , system  10  may optionally include an cage empty apparatus  120  for emptying the stunned birds from the cages  2  that are moving along the path  14 . The cage empty apparatus  120  may comprise an unload table  122  that is positioned along the path  14  after stations  110 ,  112 ,  114 , and below the upper support plane  22  of the conveyor  20  so that the top 124 of the unload table  122  does not interfere with the regular movement of cages  2  along the path  14 . The unload table  122  may be movable in a vertical direction, with a first portion  126  of the table  122  moving in an upward direction to a greater degree or distance than a second portion  128  of the unload table  122 . The support plane may be inclined to an orientation of approximately 45 degrees with respect to the horizontal. The tipping of the cages  2  on the unload table  122  may thus cause the birds in the cages  2  to fall out of the cages  2  onto an unload area  130  that is positioned at or below the conveyor  20  that direct the birds to an area where the birds can be further processed, it being understood that cages  2  are supplied with gates or side portions that are unlocked from their closed position before or during the emptying process. After the birds have moved out of the cages  2 , or after a predetermined period of time, the unload table  122  may return to the substantially horizontal orientation. The apparatus for moving the unload table  122  upward is known to those skilled in the art, and may include at least one actuator that pivots the unload table above an axis located toward one end of the table  122 . 
     Finally, once the cages  2  are emptied, as shown in  FIG. 10 , system  10  may optionally include a cage washing station  142 . Cage washing station  142  optionally comprises a washing apparatus for washing the cages  2  moving along the path  14  after the birds have been unloaded from the cages. The conveyor  20  may extend through the washing apparatus, with cages  2  preferably retaining the spacing therebetween that exists in the earlier stages or sections of the system  10 . In the washing apparatus section of the path  14 , the conveyor  20  extends past a spraying assembly  144  that directs a fluid flow toward and through cages  2  moving along the path  14 . The spraying assembly  144  may comprise a plurality of sprayers  146 ,  148  that are positioned on at least one, and preferably both, sides of the path  14  and are oriented to direct cleaning fluid inwardly toward the path. The plurality of sprayers  146 ,  148  may be arranged in a plurality of stations, and illustratively the spraying assembly includes three stations  150 ,  152 ,  154 . In one embodiment of the invention, the conveyor  20  has vertical undulations that raise and lower portions or sides of cages  2  as the cages move along the path  14  between the plurality of sprayers and through the stations. Illustratively, the first lateral side of the conveyor  20  may undulate upwardly for the first location  150  of sprayers, while the second lateral side of the conveyor may remain at a lower level relative to the first lateral side, such as, for example, a level that is substantially the same level as the conveyor entering the washing apparatus  142 . By this structure, cages  2  are effectively tipped or rotated toward the second lateral side of the conveyor, and sprayers located on the second lateral side are able to more effectively spray into the interior of cages  2  through the tops of the cages. At the second location  152  of sprayers, the conveyor along the second lateral side may undulate upward, while the conveyor along the first lateral side is located at a relatively lower elevation, thus functioning to tip or rotate the cages  2  on the conveyor toward the first lateral side of the conveyor. Sprayers located on the first lateral side of the conveyor are then able to spray into the interior of the cages through the tops of the cages. At the third location  154 , the upper support plane  22  of the conveyor  20  is substantially level, and sprayers located at both lateral sides of the conveyor are able to spray into the cages at equal effectiveness. 
     After passing through the washing apparatus  142 , the cages  2  may move off of the ending  18  of the path  14 , and may drop onto a surface as the chain of the conveyor  20  turns downwardly and moves in an inverted orientation toward the beginning  16  of the conveyor. 
     Optionally, the system  10  may include a camera  156  that is positioned to take a picture of the cages and the birds therein at the final station, which is the third station in the illustrative embodiment, to verify that the birds are stunned after being moved through the final station  114  of the stunning apparatus. 
     As a further option, where variable times of exposure are desired in different stations, the distance between the entry  78  and exit  80  openings of the chamber  64  of the stunning stations may be different, so that the time that each of the cages are in the plenum chambers is varied between the stations if the conveyor moves at a constant speed. For example, the distance between the entry and exit openings of the third stations  114  is approximately three times the distance between the same elements of the first station  110 , and the distance between the entry and exit opening of the plenum of the second station  112  is approximately twice the distance between the same elements of the first station  110 . In such a configuration, the cages  2  moving along the path  14  will spend approximately three times as much time in the third station  114  as the first station  110 , and approximately two times as much time-in the second station  112  as the first station  110 . 
     With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art in light of the foregoing disclosure, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. 
     Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.