To manage a poultry processing plant well, any good plant manager needs to understand the administrative and operational processes, and the physical characteristics of the birds being processed.

While veterinarians have a good understanding of broiler physiology, this is not always the case with poultry plant managers.

Yet understanding this physiology can help managers to adjust plant management to ensure that the sanitary and physical qualities of the processed bird are kept as high as possible, along with yield.

There are several key aspects and activities along the processing chain where adjustments to reflect how broilers function can result in improved outcomes for the plant manager.

Working to minimize heat stress

Birds do not have sweat glands, meaning that they cannot sweat when temperatures are high, making them more vulnerable when temperatures rise.

Today’s modern broiler may also be more sensitive to temperature as it is harvested a younger age – on average 42 days – and so has not had the time to develop defense mechanisms to new unfavorable conditions, including high temperatures, overcrowding, capture, transport and storage.

Yet even young birds will seek to eliminate heat when temperatures rise.

For example, heat will be lost from the broiler via radiation when its surface temperature is higher than that of the environment. A simple way of reducing environmental temperature is to place blocks of ice in the poultry house.

Broilers can also regulate body temperature through conduction via the blood flow. In hot climates, blood will be pumped to the bird’s extremities. Conversely, in colder climates, blooded is pumped away from the extremities.

Birds can also be kept cool through the transfer of heat by air currents, for example, those produced by fans. Evaporation of heat occurs from the membranes that cover the bird’s airways.

When broilers have been harvested and caged, the only heat loss mechanism that will effectively lower their body temperatures is evaporation, and this is why they pant.

Placing fans directed toward the caged birds while they are still on the farm will help to dissipate heat and, once broilers have been loaded onto trucks, there must be adequate ventilation to allow air flow during transported.

It is worth remembering that if birds have come from open houses, they will have been able to behave in various ways to help regulate their temperature. They move less, or lie down, they raise their wings and feathers to allow air to circulate closer to the skin, they eat less to slow their metabolic rate. Additionally, they may consume more water or dampen the comb, wattles and feathers.

These behaviors will not be possible once harvested, and must be compensated for.

Risks of poor feed withdrawal

Feed withdrawal normally lasts 8-12 hours. If withdrawal is too long or too short, there can be consequences at processing.

When the withdrawal period is too short, the crop can still contain feed and the intestines will be full with a rounded appearance.

This remaining ingesta pushes the intestines towards the cloaca and, because of this, it is common that, on cutting and removing the cloaca, the intestines are also accidentally cut, resulting in serious fecal contamination.

A sign that the feed withdrawal period has been too long is when mucus can be seen in fecal matter on the floor where birds are kept immediately prior to slaughter.

When the feed withdrawal period is too long, various problems can occur during evisceration.

Intestinal weakness, for example, can result in the intestines rupturing, leading to fecal contamination. The liver can darken and shrink due fat and glucose loss, while the gallbladder can increase in size and its tissues weaken. It then breaks more easily during removal, allowing bile to contaminate the abdominal cavity. Without bile removal in 15-20 seconds, indelible staining can reduce carcass quality.

Where the gizzard is concerned, dehydration can result in it adhering more firmly and becoming stained by bile. Similarly, the crop becomes more firmly attached to the abdominal cavity, making removal more difficult. Poor feed withdrawal is the reason why crop residues are sometimes found in the necks of processed chickens.


A full crop indicates the feed withdrawal period has been too short and can lead to carcass contamination.

Consequences of noise

The quiet environment enjoyed by broilers on farm is abruptly ended when the harvesting team arrives.

Some companies use diesel-powered forklift trucks to move pallets of cages during harvesting. The noise coming from this activity stresses the birds, which exhibit a flight response and pump more blood into their wings.

Once loaded onto the trucks, blood distribution returns to normal. The same response can occur, particularly where noisy forklifts are used, however, at this stage there is not time for birds to return to a completely relaxed state before slaughter.

Broilers’ wings and muscles will retain an additional amount of blood that may not be bled out. On exiting the final plucker, the skin on these parts of the carcass may have a slight red coloration, and in some processing plants this is considered a quality issue.

Overhead conveyor stress

If the breast comforter has not been properly adjusted and the area not sufficiently darkened, birds will flap their wings intensely and continue to do so until they are stunned.

Again, blood is pumped to the wings that may not bleed out and, post plucking veins will be seen still containing blood, which is a quality issue. Similarly, blood will flow to the wings if birds are kept on the overhead conveyor, affecting quality in a similar way.