Glossary of commonly used poultry layer terms

Never heard of that layer/egg term? This glossary of terms can help
calendar icon 28 October 2022
clock icon 6 minute read

We want to give credit to the original authors of this listing. It comes from USDA's Poultry Industry Manual: The Foreign Animal Disease Preparedness and Response Plan (FAD PReP)/National Animal Health Emergency Management System (NAHEMS) Guidelines

Please note: these terms will lean toward those used in the North American layer/egg market.


Completely filling a room, building or site with chickens and then completely emptying it to allow for cleaning and disinfection before the next group of chickens arrives.

Ambient temperature

The air temperature maintained in an egg storage facility or a transport vehicle.


The assignment of a value for a specific animal, arrived at by looking at the animal and considering all of its attributes and the current value of similar animals.

At-Risk Premises

Premises that have susceptible animals but none of those susceptible animals have clinical signs compatible with the FAD. Premises objectively demonstrate that they are not Infected Premises, Contact Premises, or Suspect Premises.

Battery Cages

“Battery” refers to a collection of cages.


Biosecurity encompasses procedures that reduce the probability of disease outbreaks and includes two components: bioexclusion prior to an outbreak (keeping pathogens out) and biocontainment after an outbreak (keeping pathogens from leaving an infected premises to prevent disease transmission.

Cage Free

Chickens in cage-free systems are kept indoors but do not reside in cages and have access to communal nest boxes with automated egg collection, perches, and litter.

Cleaning and Disinfection (C&D)

Practices involving a combination of physical and chemical processes that kill or remove pathogenic microorganisms – a combination that is vital for the eradication of disease.

Contact Premises

Premises with susceptible animals that have been exposed directly or indirectly to animals, contaminated animal products, fomites, or people from an Infected Premises.


Chemical products used to disperse and remove soil and organic materials from surfaces by reducing surface tension and increasing the penetrating ability of water. This can improve a disinfectant’s ability to reach and destroy microbes

within or beneath the dirt. Some disinfectants (i.e., quaternary ammonium compounds) have detergent properties.


A substance used on inanimate surfaces that destroys or eliminates a specific species of infectious or other public health microorganism, but not necessarily bacterial spores, in the inanimate environment. Disinfectants are regulated by the U.S. Environmental Protection Agency (EPA). Disinfection can also be achieved by physical means (e.g., heat, light).

Egg Breaking

Egg breaking consists of breaking the shell and separating the liquid egg contents (albumen and yolk) from the shells.


Contact with birds, equipment, personnel, supplies, or any article infected with, or contaminated by, communicable poultry disease organisms.

Exposed Premises

Premises that have been determined to be related by sound epidemiological evidence to a known infected premises, also referred to as contact premises.


All laying hens within one chicken house.

Franchise Hatchery

A hatchery which has been authorized by a franchise breeder to produce and sell products under the breeders strain or trade name.

Free Range

Chickens in free-range systems have at least some time each day when they are given access to an outdoor area


Hatchery equipment on one premises operated or controlled by any person for the production of baby poultry.

Highly Contagious Foreign Animal Disease (FAD)

A disease that spreads rapidly from animal-to-animal as well as flock-to-flock through direct contact, aerosol, oral, fomites, or vector-borne transmission. Highly contagious FADs may be recognized by above normal morbidity or mortality per unit time, where morbidity could be characterized solely by a decrease in production.


In-line egg operations are characterized by an automated egg collection system that carries eggs directly from chicken houses to the egg processing plant (building).

Infected Premises

Premises where presumptive positive case or confirmed positive case exists based on laboratory results, compatible clinical signs, case definition, and international standards.


Death of an animal; dead animals can be referred to as mortalities.

Multiplier Breeding Flock

A flock that is intended for the production of hatching eggs used for the purpose of producing progeny for commercial egg or meat production or for other non-breeding purposes.

Nest Run Eggs

“Nest run” or “off-line” eggs have been packed as they come from the production facilities without having been washed, sized, and/or candled for quality, with the exception that some checks, dirties, or other obvious under grades may have been removed.

Off-Line Egg Farms

“Nest run” or “off-line” egg farms do not have a processing facility and typically consist of one or two chicken houses which lack processing equipment. Eggs must be shipped to a processing plant at another location.

Personal Protective Equipment (PPE)

Equipment used as a barrier between an individual and a hazard that could result in an injury or occupational illness.


Domesticated fowl, including chickens, turkeys, ostriches, emus, ducks, geese, swans, pheasants, grouse, partridges, quail, guinea fowl, and pea fowl, which are bred for the primary purpose of producing eggs or meat.


Includes a tract of land, and all of its buildings, as well as a separate farm or facility that is maintained by a single set of services and personnel.

Primary Breeding Flock

A flock composed of one or more generations that is maintained fo r the purpose of establishing, continuing, or improving parent lines.

Processing of Whole Shell Eggs

Shell egg processing includes 1) washing; 2) sanitizing external egg surfaces; 3) candling/inspection of shell eggs; 4) weighing, grading and packaging shell eggs; and 5) storage and transport to market.


Immature female chickens prior to the onset of egg production.


To place animals in strict isolation to prevent the spread of disease.

Quarantined Area

During an animal health emergency, areas around infected premises may be placed under quarantine. The geographical region around the infected premises is referred to as the Infected Zone and movement restrictions for susceptible species may be implemented.

Relative Humidity

Is a ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be of both moisture content and temperature.


To treat with a product which is registered by the Environmental Protection Agency as germicidal, fungicidal, pseudomonicidal, or tuberculocidal, in accordance with the specifications for use as shown on the label of each product.


A substance that reduces the bacterial population in the inanimate environment by significant numbers, but does not destroy or eliminate all bacteria or other microorganisms.


Standard Operating Procedures that provide specific details related to various topic areas.


Poultry breeding stock bearing a given name produced by a breeder through at least 5 generations of closed flock breeding.

Suspect Premises

Premises with susceptible animals under investigation for a report of compatible clinical signs for the FAD agent.


Insects or arachnids capable of transmitting pathogens from an infected birds to another bird, usually through a bite.

Zoonotic Disease/Zoonoses

Diseases transmissible from animals to humans under natural conditions.

Reference: "USDA APHIS | FAD Prep Industry Manuals". Aphis.Usda.Gov. 2013.

The manual was produced by the Center for Food Security and Public Health, Iowa State University of Science and Technology, College of Veterinary Medicine, in collaboration with the USDA Animal and Plant Health Inspection Service through a cooperative agreement.

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