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  The high stocking density within the sheds also frustrates chickens’ natural social behaviors.

Chickens are the most intensively confined of all farmed animals.(27) Broilers are warehoused in long sheds, called “grower houses,” which typically confine up to 20,000 chickens at a density of approximately 130 square inches of space per bird.(28) Such densities make it impossible for most birds to carry out normal behaviors. A chicken requires 138 square inches just to stretch a wing, 178 inches to preen, 197 to turn around, and 291 to flap her wings.(29) As one researcher put it, “[I]t looks as though there is white carpet in the sheds—when the birds are fully grown you couldn’t put your hand between the birds, if a bird fell down it would be lucky to stand up again because of the crush of the others.”(30)

The high stocking density within the sheds also frustrates chickens’ natural social behaviors. Space is used by animals in a social context to position themselves appropriately in relation to each other.(31) Chickens have a carefully regulated social life and a cohesive social group structure. When crowded, their social system breaks down, and they have been found to be in a chronic state of stress.(32)

In addition to overcrowding, the number of birds in grower sheds disrupts the social structure of chickens. In groups of several dozen birds, such as those found naturally in the wild, chickens can establish a social hierarchy. But when housed with thousands of other birds, establishing a social hierarchy becomes impossible, resulting in a higher frequency of aggression towards one another.(33) The social chaos increases competition for resources, which may result in starvation or dehydration for weaker birds.(34)

Grower houses are commonly windowless and force-ventilated to control temperature. They are barren except for litter material on the floor and rows of feeders and drinkers. Such an environment prevents chickens from practicing many of their natural behaviors, including nesting and foraging.(35) This deprivation is believed to frustrate broilers and decrease their welfare.(36)

Overcrowded confinement also results in the rapid deterioration of air quality within the grower sheds. As the weeks pass, chicken excrement accumulates on the floors. As bacteria break down the litter and droppings, the air becomes polluted with ammonia, dust, bacteria, and fungal spores. High ammonia levels cause painful skin and respiratory problems in the broilers, as well as pulmonary congestion, swelling, hemorrhage, and even blindness.(37) Ammonia destroys the cilia that would otherwise prevent harmful bacteria from being inhaled. As a result, chickens “are inhaling harmful bacteria constantly” and develop respiratory infections, such as airsacculitis.(38) To minimize these problems, ammonia levels should not exceed 20 parts per million.(39) However, actual ammonia levels regularly exceed this amount.(40) During the winter, when ventilators are closed to conserve heat, ammonia levels may be as high as 200 parts per million.(41)

Chickens have an acute sense of smell they use to perceive their environment. Ammonia fumes inhibit this sense. As one animal scientist put it, “For a bird with an acute sense of olfaction the polluted atmosphere of a poultry house may be the olfactory equivalent of looking through dark glasses.”(42)

In such overcrowded conditions, factory farmers accept that many chickens will die from disease and stress.(43) But there remains an economic rationale for farms to overcrowd the birds. “[L]imiting the floor space gives poorer results on a bird basis, yet the question has always been and continues to be: What is the least amount of floor space necessary per bird to produce the greatest return on investment.”(44)

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