January 26, 2012
AVMA policy: Laying Hens Housing Systems
A Comparison of Systems for Housing Laying Hens
Definition: A wire enclosure housing 3 to 6 birds and having a sloped floor. In commercial production however, birds are commonly housed at the density of 7 to 8 birds per cage.
Advantages:Reduced exposure to environmental and social hazards: Cages reduce the negative consequences of contact with manure, including infestation with roundworms and coccidia.1 Cages also provide protection from predators and other wildlife.Reduced proliferation of injurious pecking and subsequent mortalities: If hens begin to cause serious pecking injury2 then the small social group size in each cage limits the proliferation of pecking and subsequent mortalities that may be associated with it.Monitoring: Conventional caging improves the opportunity to monitor individual birds' health and well-being.Biosecurity: Hens housed in cage housing systems are at a lower risk of infectious disease than hens housed in litter-based systems irregardless of outdoor access.3Air Quality: Conventional caging does not incorporate the use of litter. Litter-based systems have been shown to have increased levels of ammonia, dust, and bacteria.4
Disadvantages:Restriction of natural behaviors: Hens in cages are less able to perform behaviors such as dust bathing,5 walking6 and foraging.5 Spatial restriction has also been shown to decrease the hen's performance of comfort behaviors (e.g., wing flapping, stretching, body shakes, tail wagging).6 Nesting and roosting are not options in the conventional caging systems.Variable risk—Cage-related injury: Hens may become trapped between wires, or experience foot damage secondary to overgrown claws. However improved cage designs7 and the use of abrasive strips8 largely eliminate these occurrences.Variable risk—Feather pecking: Injurious feather pecking does occur in cages, often necessitating beak trimming. Providing devices such as plastic objects in a conventional cage,9,10 or balls in the feeder11,12 has produced equivocal results; however, string tassels13,14,15,16 may have some potential to attract pecking and reduce associated injuries. Selection methods in which the genetic effect of an animal on the survival of its group members is taken into account (group selection) have been shown to be effective in reducing mortality due to feather pecking and cannibalism in laying hens.17
Summary: Cages can provide a highly controllable environment that protects hens from a range of health and injury problems; however, they afford limited space and behavioral enrichments (e.g., opportunities for perching and dust bathing) and many natural behaviors cannot be performed in conventionally-sized and equipped cages. Cages tend to have an economic advantage. Egg production,2,18,19 quality2,20,21 and efficiency22 are often greatest in cage systems.
Disadvantages:Variable risk—Feature malfunction: Each of the additional features in an enriched colony has the potential to malfunction causing injury, harboring disease vectors or parasites or provoking aggression. For example, poorly designed perches can cause increased levels of keel deformation2 and or bumblefoot.43
Summary: There are multiple models of enriched/furnished housing in use and more under development. They provide a wider range of behavioral opportunities, while conserving many of the advantages of a conventional cage. Egg shell quality35 and shell cleanliness44 are similar between conventional cages and enriched colonies with the exception of enriched colonies that are designed with scratch pad areas covered in sand or wood shavings. These designs can lead to dirtier eggs than what is seen in conventional caging.41 In addition the excretion of Calcium and Phosphorus, two minerals important to shell quality, are reduced in enriched housing situations as compared to conventional cages.45
Disadvantages:Vector exposure: Birds raised on the floor are more likely to encounter disease vectors in feces or dampened litter, potentially leading to reduced health48 and conditions such as bumblefoot.19 This may require handling of the birds to administer treatments or preventatives such as vaccination against coccidiosis.1Health: Hens in extensive systems that utilize perches tend to suffer more injuries due to landing failures when jumping from one perch to another. In addition, high usage of perches by hens can lead to keel bone deformation.44 Overall performance is more variable, depending on outbreaks of coccidiosis or pecking mortalities.49 In some cases, floor housing results in high mortality due to pecking50 but some reviews do not support this as a general finding.19Variable risk—Increased group size: Extensive housing systems typically house larger flocks with an increased risk of injurious pecking and pecking mortalities.51Air Quality: Litter based systems have been shown to have increased levels of ammonia, dust, and bacteria.4 Increased ammonia levels can cause keratoconjunctivitis and have deleterious effects on the respiratory tracts of birds.4 Dust in housing systems can be biologically active and may have microorganisms attached to the particles.4
Summary: More extensive housing allows great freedom of movement, but is often associated with more hazardous conditions such as large social groups and litter which can lead to outbreaks of disease or injurious pecking if not managed carefully.
Disadvantages: Outdoor conditions potentially expose hens to toxins, wild birds and their diseases, predators53 and climatic extremes. Hens are often reluctant to use the range area or venture far from the hen house resulting in wear of the pasture in the area near the house. Farms where the hens make less use of the pasture have higher incidence of feather pecking.54,55 More optimal pasture use can be encouraged by limiting flock size,56,57 including cockerels in the flock57 and providing cover.57,58,59,60
Summary: When access to the outdoors is provided hens are able to perform the broadest range of naturalistic behaviors, but they may also be exposed to climatic extremes, toxins and disease.
Feather pecking, peck injury and peck mortality (cannibalism) in poultry occurs at variable rates and may unpredictably become severe and cause high rates of distress, injury and death in a flock. Individual genetic selection may reduce feather-pecking, however, group selection of traits is a more beneficial way to reduce severe pecking while preserving rate of lay and longevity.58
Some housing decisions depend on weighing welfare versus non-welfare (e.g. economic and public acceptability) factors. For example, as the number of hens kept in a conventional cage is increased, the laying productivity of each hen is reduced.67 However, there may be an economic advantage to this practice because of overall increased output from the cage. Hens that produce the most eggs also suffer more from conditions such as osteoporosis.61
One key decision to be made by producers, consumers and regulators is how to balance the hen's freedom to exercise and perform natural behaviors against exposure to potential hazards such as disease vectors and large social groups. To make this judgment in a transparent manner the advantages, disadvantages and risks associated with each system should be acknowledged. The priorities of all of the stakeholders including regulatory bodies, consumers and producers should also be transparent. As the causes of health conditions like osteoporosis and behaviors such as injurious pecking are better understood the relative advantages and disadvantages of these systems will change and new systems may emerge.
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