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Authors: Robyn Gwen Alders, BVSc, Ph.D., Richard Jakowski, DVM, PhD, DACVP
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OCW Zoological Medicine 2008
Conservation Strategies and Disease (2009)
R. Alders, DVM / R. Jakowski, DVM
Cummings School of Veterinary Medicine at Tufts University

Poultry have been domesticated for thousands of years. Archaeological evidence suggests that domesticated chickens existed in China 8,000 years ago and that they later spread to Western Europe, possibly by way of Russia. Domestication may have occurred separately in India or domesticated birds may have been introduced from Southeast Asia.

The term poultry is used to designate a group of domesticated birds used for the production of eggs or meat. Species commonly defined as poultry include chickens, turkeys, ducks, Muscovy ducks, geese, swans, pigeons, peafowl pheasants and Guinea fowl. In some instances the ostrich also qualifies for inclusion in this category.

1. The US Poultry Industry

Common areas of poultry specialization in the US are:

1.1. Commercial broilers

Since 1938 the commercial broiler industry has fostered the genetic development of chickens for rapid growth and better quality meat production. Their achievements have been outstanding when one considers some important facts. In the late 1930's it took 12 - 15 weeks to produce a 3 - 4 pound broiler. These birds were either sold live to the consumer or butchered and dressed while the consumer waited. The cost was around $1.00 per pound (live weight). The modern broiler reaches the same market weight in 4 - 5 weeks with an average cost to the consumer of around $0.75 per pound of packaged meat.

1.2. Commercial egg laying birds

Genetic improvement of the commercial egg laying hen has also been spectacular. The modern egg producing chicken will produce 240 - 270 eggs per year.

Commercial broiler and egg production are intense agribusiness operations. Chickens are housed in large numbers (10,000 - 100,000 birds per room) where the air is filtered to prevent entry of common poultry pathogens. Temperature, humidity, air quality and lighting are carefully controlled to maximize production and minimize the likelihood of disease. As might be expected these operations are highly vulnerable to virulent disease outbreaks. Billions of dollars have been lost when highly pathogenic avian influenza and velogenic Newcastle disease occurred in the US. These operations often employ one or more company veterinarians or rely on the services of a state poultry diagnostic laboratory. The private veterinary practitioner rarely if ever gets involved with commercial poultry operations.

1.3. Turkeys

Within the last 15 years commercial turkey production has dramatically increased. Turkey meat is no longer a specialty for the November - December holiday market. High intensity rearing of large numbers of turkeys naturally increases the risk for disease. Currently most commercial turkey production takes place in Minnesota. A large number of turkey farms are also found in Vermont, but these producers are primarily geared to the Thanksgiving and Christmas markets.

1.4. Commercial poultry breeding

This industry provides breeding female and male birds for continually improving genetic stock for increased meat or egg production. It require about five years to implement the efforts of a single genetic manipulation from the time of initial research until the practical use of this trait in the form of increased production in eggs or meat. Although the goal of the commercial poultry breeder has been directed toward increased production yields in the past, recent advances in genetic research have led to interests in producing genetic strains that are naturally resistant to many of the common poultry pathogens.

1.5. Waterfowl

The commercial duck and goose industry focuses on production of roast duckling and liver pate. Compared with commercial chicken and turkey operations this market is relative small because of the limited demand for these foods. Goose down used in the manufacture of the sleeping bags and ski apparel is a by-product of the commercial waterfowl industry.

1.6. Fancy chickens

This hobby is pursued by small but active groups of poultry enthusiasts. Chickens in this category are kept primarily as pets. There are more than 20 different exotic breeds of chickens in this category. The raising of fancy chickens is often a highly competitive activity with emphasis on the winning of ribbons at county, state and national competitions. Flocks are small, usually less that 50 birds. Fancy chicken raisers need veterinary advice on vaccination and disease control because of the co-mingling of birds from many locations which occurs during judging competitions.

1.7. Pigeons

Pigeons are kept as show birds similar to fancy chickens. They are also flown in racing events where these birds will fly race courses of many hundreds of miles sometimes as long as 600 miles. These races often result in severely stressed birds which are then more susceptible to disease when they are housed with birds from many other flocks.

1.8. Specialty birds

Pheasants, quail and other game birds are often raised by a few growers who produce meat for a limited, gourmet market. Open range production is usually employed in these operations and skill required in the management of such birds in order to prevent diseases which would result in economic disaster to a small operation.

Game birds also include fighting cocks. Owning fighting cocks is not illegal but even though the practice of holding fight cock contests is illegal, it remains a major source of income and social activity for a number of societies across the US.

1.9. Small (backyard) flocks

Small, backyard chicken flocks represent the most frequent involvement with chickens for the private veterinary practitioner. These flocks usually contain birds of several age groups. The owner usually knows very little about basic poultry husbandry, nutrition or disease control. The practicing veterinarian who is interested in pet bird diseases can be very helpful in these situations, consequently, disease problems emphasized in this course will be the ones often encountered in the small, backyard flocks.

A small collection of chickens, typical of a "backyard" flock. Fencing is strongly encouraged to decrease the opportunity for predation.
A small collection of chickens, typical of a "backyard" flock. Fencing is strongly encouraged to decrease the opportunity for predation.

2. GLOSSARY – a few poultry terms worth knowing

breeder : An adult hen used for the production of fertile eggs subsequently incubated to produce chicks.

broiler : A chicken raised for meat production.

brooder : A stove for keeping baby chicks warm. This is usually used when chicks are raised in cold climates and is required until they reach 4 weeks of age.

broodiness : Maternal instinct in a hen which results in her setting on eggs with resultant incubation and the hatching of chicks. Broodiness is an inherited characteristic; hard to find in this day and age when chicks are artificially incubated and never getting to see mom.

capon : A castrated male chicken. cockerel: Male chicken under 20 weeks of age.

drake : A male duck.

feed conversion : In a broiler the number of pounds of feed required to produce one pound of live bird weight. In a laying hen the number of pounds of feed required to produce a dozen eggs.

gander : A male goose. hatchability: Percent live chicks obtained from the total number of eggs set.

hatcher : Machine for hatching eggs incubated from 18 -21 days.

incubator : Machine for incubating eggs from 1 - 18 days.

Incubation Times for some Common Poultry Species


Incubation time (days)





duck (non-Muscovy)


Muscovy duck


goose (small variety)


goose (large variety)


Japanese quail


bobwhite quail






Guinea fowl


layer : Female chicken over 20 weeks of age.

molt : The normal physiologic loss of feathers that occurs in a cyclic pattern in all birds. Stress and disease can precipitate molting before it should normally take place.

poult : A young turkey or pheasant.

pullet : Female chicken, usually under 1 year of age.

roaster : Chicken raised for meat production, usually to a weight of 6 - 8 pounds.

rooster : Male chicken over 20 weeks of age.

snood : The fleshy protuberance at the base of a turkeys' bill.

spent fowl/hen : An aged commercial laying hen, usually 60 - 90 weeks of age

3. Chicken Husbandry and Nutrition

3.1. Feed

From hatching until 5 weeks of age young, rapidly growing chicks require a high protein diet composed of at least 20% protein and fortified with adequate vitamins and minerals. This is usually supplied in the form of a commercial diet referred to as grower or growing mash. At 20 weeks of age a less costly, lower protein ration is fed to laying hens. It is called laying ration and should contain a least 16% protein.

3.2. Lighting

From one day of age until 20 weeks birds should receive at least 8 - 10 hours of light per day. For peak egg production 16 hours of light per day is necessary.

3.3. Water

The need for water is so obvious that it almost seems silly to mention its importance. Yet, the water supply of many flocks is often inadequate because of high consumption rate in hot weather or freezing during winter months. Chickens need water for survival, growth, activity and egg production. Every 4–5 chickens will drink about 1 liter of water every day and they will need more than this when it is very hot. Water should be available at all times. Although chicks can survive for several days without feed, they will quickly die without access to water. Complete water deprivation may result in death in less than a day during hot weather. The quality of water is just as important as the amount supplied. Dirty water that is not replaced daily is as bad as no water. Inadequate water can quickly result in stress that will often precipitate feather molting and the cessation of egg production.

3.4. Temperature

Newly hatched chicks require an ambient temperature of 95°F. The temperature is then lowered 5°F per week until the chicks are fully feathered at 5 weeks of age.

3.5. Space

Chickens raised in an indoor environment should have at least 1 square foot of space per bird to prevent overcrowding.

3.6. Ventilation

An adequate supply of fresh air is sometimes a problem when chickens are raised indoors. Dust, ammonia and high humidity are potential problems if birds are raised on litter, especially during the hot summer months. In some instances the ammonia levels can be so high at ground level that severe lacrimation and corneal ulcers may result.

3.7. Molting

Molting is the term used to denote shedding of old plumage ( ecdysis ) with subsequent replacement by new feathers ( endysis ). The process is initiated by new feather growth which pushes the old feather shaft out of the feather follicle. Therefore, feather molting is a passive process. Feather loss in adult chickens is a indication that molting has begun. Knowing the approximate date when molting begins is helpful to the egg producer because it helps to predict when molting is complete and the hen will commence egg laying. It takes approximately 6 weeks for a new feather to completely grow out.

Molting birds utilize a substantial amount of dietary protein for feather growth. Since this protein is not available for formation and growth of eggs, a drop in egg production is almost always associated with the molting period. Poor producers frequently stop laying altogether.

Adult chickens undergo one molting cycle per year. The process is controlled by the photoperiod, under natural light it occurs in the late summer and fall. Commercially reared chickens are housed under artificial light and the normal molting is suppressed but even in these flocks it still occurs about once a year. Some molts are complete, involving all feather tracts; others molts are partial and only involve specific tracts. Typical molts usually affect the feather tracts in the following locations: neck, breast, body, wings and tail. Pullets often undergo a partial neck molt after laying for 2 -3 months. This can turn into a generalized molt if the light is not increased. High protein feeds may hasten the onset of molting but these feeds also hasten the molting process and return birds to peak production sooner than if a lower protein feed is used.

4. The Poultry Industry Internationally

Poultry production is the fasted growing livestock subsector. Chickens are the most important species but duck production is significant in parts of the world such as Southeast Asia.

Backyard or scavenging poultry are commonly raised in many countries and constitute an important part of household livelihood strategies. These birds are frequently managed by women and children and can contribute to household food security, poverty alleviation, HIV/AIDS mitigation and wildlife conservation.

5. Support resources and continuing education

5.1. Professional organizations

Association of Avian Veterinarians

American Association of Avian Pathologists

American College of Poultry Veterinarians

Poultry Science Association

5.2. Continuing education resources

Annual conferences of professional organizations above

5.3. Formalized Training/Board Certification

5.3.1. Training Programs and Residencies

See ACPV site

5.3.2. Board Certification

American College of Poultry Veterinarians

6. References and Resources

6.1. Books and Journals

Diseases of Poultry . 12th ed. / edited by Y. M. Saif, Iowa State University Press, 2008.

Jordan, Frank T.W. Poultry Diseases , 5th ed. Bailliere Tindall, 2002.

6.2. Websites

APHIS - The National Poultry Improvement Plan

American College of Poultry Veterinarians

FARAD - Producers Guide to Residue Avoidance Management

International Network for Family Poultry Production

International Rural Poultry Center

Poultry Breeds

Poultry NetVet

World Poultry Science Association