The importance of operations prior to poultry slaughter should not be underestimated if the ultimate goal is to produce a high-quality carcass.
Firstly, there is the matter of feed withdrawal. Under normal conditions, the time between feed withdrawal and slaughter is 8-12 hours, while the water supply should not be terminated.

There are two incorrect feed withdrawal situations — short feed withdrawal: less than 8 hours, and long feed withdrawal: more than 12 hours.

Signs of atypical feed withdrawal at processing  

A short feed withdrawal can be identified by the following characteristics, which can be seen after plucking the bird and during evisceration:

  • After chickens are plucked, the crop is visibly enlarged. This is due to an excessive feed content;
  • Intestines are full and they are located closer to the vent. This organ also exhibits a slight increase in size; and
  • During evisceration, the proventriculus and gizzard are found to be full of feed.

Long feed withdrawal is the otherside of the coin. It causes significant dehydration problems and the effects on the affected organs are visible during evisceration.

Intestines : If red particles (resembling little pieces of tomato skin) are observed in the feces on the floor of the plant’s storage area, then the intestine’s mucosal layer is being evacuated. In this case, during evisceration, the intestines tend to break, even if handled (either manually or automatically) with care. This results in fecal contamination.

Gallbladder : The gallbladder reaches its maximum size during prolonged withdrawal. The tissue becomes very fragile and it easily breaks, despite careful handling. Once the gallbladder is broken, bile spills inside and/or outside the abdominal cavity. If the carcass is not washed immediately, the bile may leave an indelible stain.

Liver : This organ is the chicken’s energy reserve: it contains glycogen and fat. When this reserve is depleted, the liver shrinks and turns dark red. In addition, the taste becomes a little bitter, due to the action of reverse peristalsis.

Gizzard : The gastric cuticle increases its adherence as a result of the dehydration process, consequently more pressure on the peeler rollers will be needed to remove it. This problem represents a loss of gizzard meat of around 20%, which affects the final yield of the process: carcass and giblets.

Crop : Dehydration causes the crop to attach firmly to the abdominal cavity, resulting in more effort from the personnel in order to remove it.

Effects on quality, safety and yield  

Certain problems become evident when the feed withdrawal period is too short.

Among these will be variability in the average live weight. This can be a major problem in fulfilling customer orders as there will be high variability in carcass weights.

Additionally, should a bird fail to convert its last meal into meat, there is a waste of resources. When the withdrawal period it too short, there is a high risk of feed and/or fecal contamination during evisceration.

A long feed withdrawal period also presents its own problems. It can directly impact on quality, for example, physical appearance and carcasses with green spots; safety, as there is a high risk of bacterial contamination; and yield, due to the weight loss in gizzards and livers.

Before stunning  

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Immediately prior to electric stunning, a number of factors need to be taken into consideration.

For example, the voltage and electric current need to be adjusted according to the average weight of the bird. Similar adjustments should also be made for transit time and bath height.

The hanging area should be lit using special blue lights, and the breast comforter should be adjusted to ensure contact with the chicken’s breast.

To prevent excessive build up of blood in the neck and wings, the time between hanging and entry into the water bath of the stunner should be between 20 and 30 seconds. The entry ramp to the water bath should be kept clean and dry to prevent pre-shock. Failure to do this will result in birds lifting their head and wings and avoiding the bath. Additionally, the metal shaft at the top of the shackles must be in permanent contact, to ensure a closed electric circuit.

A failure to properly address the above points can result in the following:

  • Poor bleeding and instant death due to an excessive electric current;
  • Insufficient bleeding time as some birds will enter the scalder still alive;
  • Fragile thorax bones that are easily broken;
  • Breast hemorrhages;
  • Birds that are not fully relaxed. The higher muscular contraction affects plucking operations, and
  • Thigh hemorrhages, femoral bone and artery breaks.

Scalding  

Scalding is carried out to prepare the skin of birds, through protein denaturation, prior to feather removal. To ensure that this is carried out effectively, a number of variables need to be constantly monitored:

  • Transit time and water temperature determine the color of the processed carcasses’ skin -- either white or yellow.
  • Water agitation and immersion of the bird during its transit through the scalder, both of which help open the follicles and loosen the feathers.

A variety of factors affect the performance of scalding operations, including whether a scalder is open or closed.

Some research has shown that a closed scalder can save between 20% and 30% of energy costs. Less fuel is needed to operate the boiler and water temperatures can be 1-2C lower than in open scalders. Using a closed scalder minimizes breast over-scalding problems.

  • When chickens float during the scalding process, the water temperature needs to be increased by a couple of degrees to ensure that plucking can be carried out effectively. This is particularly important for tail and wing feathers.
  • If water agitation is not uniform along the chicken’s transit through the scalder, the water will not be able to properly penetrate the dense feather cover and reach the skin.
  • If the water temperature is not reasonably even, (a maximum +/- 0.2 C), the plucking operation is affected. Particularly with yellow chickens: a loss of the epidermis may occurr in several areas.
  • Sanitary ante-mortem conditions. When birds enter the scalder with the feathers and skin contaminated with fecal matter, there can be rapid increases in the bacteria population if no proper control measures are taken.
Consequences for quality, safety and yield 
  • Lack of skin color uniformity across the carcass;
  • Incomplete plucking;
  • Over-scalded-breat;
  • Loss of subcutaneous fat - water agitation in the chiller turns the fat into foam, which represents a loss of yield as high as 2.0%; and
  • When subcutaneous fat is lost, the skin (especially on the breast and upper thigh) becomes fragile and prone to tearing during the plucking operation.

Plucking  

Successful plucking depends on the effectiveness of the stunning and the scalding processes, therefore, the following aspects should be monitored:

  • There should be a minimal distance between the exit of the scalder and the entrance to the plucking machine; and
  • The number of plucking machines should be determined by the speed of the line and the type of chicken to be plucked: yellow birds require more plucking capacity.

Effects of inadequate plucking  

When feathers are found on carcasses and need to removed, bottlenecks can occur in critical areas such as the packing area. Consequently, there can be production stoppages, loss of water uptake, and a resulting increase in carcass temperature can result in bacteria growth.

Skin can be torn due to higher pressure being exerted by the rubber fingers. In these cases, most of the carcasses will end up being grade B or C.

There is also the issue of cross-contamination. Higher pressure against the skin helps bacteria enter the follicles.

A good understanding of the various relationships across processing operations, and contiuous control and monitoring, will help to guarantee a processed carcass with high quality, safety and yield.