Various factors can affect the quality and yield of birds at the processing plant and, while some of these may be beyond the immediate control of the plant manager, it does not mean there are not solutions.

Accounting for geography

Take, for example, atmospheric pressure, which decreases as one moves away from sea level. The higher one goes, the greater the number of red blood cells needed to supply oxygen. The increase in the number of red blood cells brings with it changes in blood viscosity.

However, other changes also occur. When blood is pumped into arteries, their diameter remains unchanged as their four walls are rigid enough to cope with any additional volume of blood. This, however, is not the case with veins as, despite having the same number of walls, two of those walls are thinner. Consequently, any additional volume of blood passing through veins will result in their expansion.

It is worth keeping the above in mind when attempting to solve some the difficulties that can occur at processing, particularly with wings and breast meat, when birds are reared and processed in cold climates or at higher altitudes.

It is also worth remembering how blood is distributed within the chicken. Blood vessels carry 84 percent of the blood, while the organs account for 16 percent. The distribution of blood within the vessels can be further broken down to 64 percent being in the veins, 15 percent in the arteries and 5 percent being in the capillary vessels.

It is easy to see that the majority of blood is in the veins, and it is worth remembering also that wings contain little muscle mass and, because of this accumulated venal blood, is much more visible and can lead to chickens being condemned at the quality control stage.

However, there is another consequence that can occur when chickens are reared in cold weather, and this is that blood vessels become constricted to retain heat within the body of the bird. 

These difficulties, however, can be overcome by increasing bleed time, and usually extending the period to three minutes and 30 seconds is sufficient. Under certain conditions, it can even be extended to four minutes. This allows the drainage of excess blood and counteracts the effects of vasoconstriction.

Yet there remain procedural issues that can further affect condemnations as far as blood is concerned, and these include the time that elapses between hanging a bird on the shackles and its entry into the stunner; the degree to which birds flap their wings once in the shackles and the factors that contribute to flapping. For example, if birds are handled by the legs, they will flap in an attempt to free themselves. The same reaction occurs when they are held by the neck.

The accumulation of blood in the wings and breast that occurs at this stage of processing and reach critical levels, so is worth reviewing.

Ensuring smooth, swift passage

Leaving a bird on the shackle for longer than 30 seconds will result in blood accumulating in the wings due to the simple forces of gravity. Therefore, it is recommended that time to stunner entry be no more than 20-30 seconds.

Should the hanging area not be properly darkened, the breast massager not properly adjusted, and the handling of birds performed without care, wing flapping will increase. This intense movement results in the heart pumping a greater volume of blood to the breast and wings so supply oxygen to the muscles. This means that increased volumes of blood will be present in these areas and should be factored into bleed time.

It is also worth remembering that birds will have intensely flapped their wings during capture leading to additional blood being pumped to the wings.


If a minimum bleed time of between three minutes, 30 seconds and four minutes is adopted, depending on the temperature, atmosphere, altitude, degree of flapping, etc., a greater amount of blood will be drained from the breast and wings. This will improve the appearance of the bird almost to the point of appearing as if it had been reared and processed in a warm climate, where blood is less viscous and vessels not constricted. It is worth remembering that blood accounts for three percent of the weight of the live bird.

Spotting the signs

A simple way of monitoring whether bleed time is sufficient in a cold climate, monitor birds between their exit from the plucker and their entry into the first stage of the evisceration process.

If a lot of blood can be observed on the equipment, in troughs or on the floor, then bleed time needs to be increased.

When judging the appearance of wings, small red marks can be indicative of problems pre-stunning.

Red marks can be the result of chickens en route to the stun bath coming into contact with the ramp, which can be damp and so conducts electricity. In reaction to this, birds raise their necks and flap vigorously. They will continue to do this until they exit the stunning area, and they will exit still conscious, with significant implications for slaughter.

It also should be remembered that there is only a very short distance between each shackle, so the wings of one bird will frequently be in contact with those of another, and they may even become intertwined. Additionally, birds may flap within the stunning cabinet. All of these actions can lead to hematomas in the wings.

To ensure product quality, flapping needs to be minimized. Should birds flap forward, their wings may hit against the stunning cabinet. If they flap backward, they will flap against themselves, the breast comforter and eventually the stunning cabinet.

Given that wings have little muscle mass, the effects of these sudden impacts are accentuated.

If these problems are allowed to continue, they can result in the condemnation of large quantities of wings that have a significant market value, and to prevent their occurrence slopes similar to those seen at the scalder can be installed before and after the stunning bath.

But to ensure product quality, it is also worth reviewing plucking operations. The hardness of fingers, and angle at which carcasses come into contact with the fingers, and the pressure applied will all influence whether birds become bruised. It is also worth keeping in mind that the use of warm water at this stage also help to lessen problems.

Some feathers are more difficult to remove than others. Because of this, fingers of varying hardness should be used. For example, for the upper area, harder fingers need to be employed, for the central region, soft fingers, and for the wings, semi-hard fingers.

When setting the plucker, if viewed from above, it should resemble a cone – broad to begin with when the birds have full feather cover, and narrowing towards the exit when most feathers have been removed.