How broiler physiology impacts poultry yields

Broiler physiology at poultry processing needs to be properly taken into account to ensure the smooth operation of the processing plant.

Issues with feed withdrawal need to be communicated to the evisceration team. | Bigstock, franz12
Issues with feed withdrawal need to be communicated to the evisceration team. | Bigstock, franz12

Understanding poultry physiology can help to make poultry processing plants run more smoothly, and prevent some of the issues that might otherwise lead to a decrease in yields.

This knowledge, and paying careful attention to detail at certain key points from pre-harvest to processing, can ensure processed chicken production remains within the parameters and rules set by each company or relevant authority.

Feed withdrawal

Broilers normally eat every four hours, but not all birds will eat at the same time and, with this in mind, it is easier to understand why feed withdrawal is never 100 percent effective.

The success of feed withdrawal can never be consistent across the flock, irrespective of whether the withdrawal period is long or short. It is worth remembering that, at the moment that the feeders are raised or closed, 8-12 hours prior to slaughter, some chickens will be eating, while others will be walking about or laying down, having already eaten.

Feed, once ingested, takes four to four-and-a-half hours to pass through the birds' system and, for this reason, it is recommended that broiler harvesting be carried out five hours after access to feed, although not water, has been stopped.

Prior to capture, birds should be kept active. This can be achieved by staff walking the poultry house, but this must be done slowly and calmly.  

If this last point is ignored, birds will panic and attempt to escape from this source of stress, making short flights and walking on top of each other. Intense wing flapping can put extreme pressure on blood vessels, which may break, leading to bleeds. Wings may be bruised as birds knock against each other or against the feeders and drinkers in their panic to escape. Skin may also become scratched. Should birds become particularly stressed, then the fragile bones of the thorax may break.

All of the above can lead to carcasses being rejected at the processing plant.


Birds must be captured with care. Broilers should be firmly held with their wings pressed to the body to prevent flapping, but not so firmly as to impede breathing. 

Care must also be taken as they are placed into crates, to minimize aggression from birds that have already been crated. 

If stacked trays are used, they should be filled from the top down to avoid harming animals as they are put into the metal framework. If filled from the bottom upwards, the risk of birds being knocked increases. 

During transport 

Once birds are caged or in containers, the temperature within the container will rise. This temperature will rise further still once the crates are loaded onto the trucks, and if the trailer is not properly ventilated or air-conditioned, the birds will suffocate. 

At the processing plant 

The receiving area should have adequate air conditioning to remove the build-up of heat and prevent birds from dying from heat stress. 

While at the birds are held in this area, it should ve possible to see whether there has been an adequate feed withdrawal. This can be judged simply by looking for residues mucosa or sub intestinal mucosa that will have a red appearance. Should this be evident, the receiving area supervisor can inform the dead of evisceration, who will then know the risk of fecal or feed contamination will be higher. 


The head should be first part of the broiler to come into contact with electricity shock. The broiler will struggle and lift its head and this may lead to it not entering the water and the bird not being stunned. This will have an impact on slaughter and bleed out, or the bird may enter the scalded still alive. 

Bleed tunnel 

It is common that two different sizes and weights of broilers are processed within a single shift. To accommodate this, the height of the water bath can be adjusted, along with the voltage and amperage. 

However, despite such adjustments, at times even if a new batch of birds has the same average weight as the preceding batch, birds may enter the bleed tunnel with their wings flapping. 

When this occurs, the exit from the last plucker should be checked to see whether the birds in the batch had full crops. Chickens do not have diaphragms and, for this reason, when hung bu the legs, should the feed withdrawal period have been too short, feed will pass back through the esophagus, placing pressure on the trachea and making breathing difficult. It is this sensation of drowning that cause the birds to move their body and wings. 

Eduardo Cervantes LĂłpez is an international consultant based in Colombia. He can be contacted at [email protected] or via

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