How to align stunning, slaughter to broiler physiology

A properly managed stunning and slaughter process aligned to broiler physiology helps to ensure highest yields in the poultry processing plant.

When birds are not properly bled, they will have a reddened appearance.
When birds are not properly bled, they will have a reddened appearance.

This article appears in the October issue of Poultry International. View all of the articles in the digital edition of this magazine.
 

In our previous processing feature, we looked at how adjusting various operations to a broiler’s physiology during the earlier stages of poultry processing can improve final yield, and now we look at how operations further down the processing line can be similarly adjusted to optimize broiler yields.

Properly implementing stunning

A great deal of care and attention needs to be paid during stunning, given the number of variables.

When, for example, there is insufficient current to guarantee a good stun, there will be increased muscle contraction.

This muscle contraction can make plucking more difficult, and is one of several factors that can result in feathers being present on carcasses at the packing area. It is also worth noting that, as carcasses cool, any remaining feathers will be more tightly retained, and their removal requires additional time and effort, affecting the cost per kilo of processed meat.

Time in the stunning bath

Studies have shown that the ideal time for the broiler to remain in the stunning bath is 10-12 seconds. The heart, which normally beats at 350 beats per minute, will slow to about 112 beats per minute, a decrease of 32 percent.

Once the bird exits a bath, a pause of 10-12 seconds is needed prior to slaughter. If the blood vessels are cut too quickly, the volume of blood expelled at the start of bleed-out will be lower, as the heart will not have had time to return to its normal rhythm.

Given that the bleed tunnel is of a fixed length, if bleed-out is delayed, then blood will fall onto the floor and onto evisceration equipment. Conversely, if there is more than a 12-second delay, total bleed time is reduced, meaning that some of the blood that should be drained remains in the carcass. In this case, birds may enter the scalder alive, adding to the number of rejected carcasses.

Achieving a good stun

For a stun to be considered good, birds should exit the stunner unconscious, and there should be no bruising in evidence when birds exit the plucker or at cut-up. Particular attention then should be paid as broilers exit the stunner and pass through the automatic head and neck guides prior to the neck veins being cut.

In many instances, birds can be seen to be shaking at this stage. This is known as the tonic phase. Subsequently, they will relax and stop shaking, entering the clonic phase.

When these reactions have not been properly understood, plant managers may increase the voltage and amperage in the stun bath to stop birds from exiting “awake.” This, however, can increase bruising around the thorax, wings and breast, adding to the volume of material rejected.

Broiler slaughter

Immediately post-stun, particular attention needs to be paid to broiler physiology at slaughter.

If the trachea is also cut when the neck veins are cut, the bird will stop breathing. Consequently, the brain will stop functioning, and no signals will be sent to the heart to continue pumping blood. Blood will then accumulate in the neck due to the force of gravity.

A similar situation arises if the spinal cord is cut, as the brain will not be able to communicate with the heart and blood will similarly accumulate in the neck. Carcasses will then tend to take on a reddened appearance in this area and can no longer be classed as Grade A.

Bleed out

Climatic temperature affects the quality of bleed-out.

It is worth remembering that one of the ways in which chickens regulate their body temperature is via conduction. In hot climates, blood will be pumped toward the skin and blood vessels will widen to dissipate heat. In cold climates, the opposite occurs.

Because of this, when calculating bleed-out time, local temperature conditions need to be taken into account. In general terms, bleed-out times in hot climates is shorter, as more blood is lost more quickly. Around two and a half minutes tends to be sufficient. In cold climates, however, bleed time can be as long as three and a half minutes, due to vasoconstriction.

Height above sea level also impacts bleed time, due to lower levels of oxygen and the broiler’s physiolocical response. Birds at higher altitudes may even have a slight reddish tinge to the wings and skin because of this. At high altitudes, bleed time may need to be extended to four minutes.

Entering the scalder alive

Any live birds entering the scalder will take in water and be contaminated, due to the scalder containing water with high levels of bacteria due to fecal contamination. Additionally, the high temperature of the water will bring any remaining blood to the surface and, once birds are plucked, they may have a reddish appearance, particularly around the tail.

Poor stunning and plucking

Too much current leads to greater muscular contraction. Given that the wing and tail feathers begin in muscles, if there is greater contraction, they will be harder to pluck, and the plucking machine will need to be adjusted.

Additionally, too much current results in dilation of the blood vessels, particularly of the more flexible veins. This can be particularly obvious around the wings and thighs. During cut-up and deboning, bruises may be found, particularly in the breast, given that the thorax contains many fragile bones that are easily broken and can cut the blood vessels supplying tissues. When this occurs, bruised tissue must be removed, so lowering yields.

Feathers Wings 1610 P Ipoultryprocessing2

Any feathers remaining on the birds after plucking could indicate that birds have been overly stunned.

 

How broiler physiology affects processing quality

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