Chicken, scientifically known as Gallus gallus domesticus, is a domesticated red junglefowl species hailing from Southeast Asia. Through hybridization with other wild species of junglefowls (including the grey junglefowl, Ceylon junglefowl, and green junglefowl), the chicken has evolved into a distinct and diverse bird containing many different breeds and subtypes. Known as a "rooster" or "cock" once it reaches maturity, and a "cockerel" while still young, castrated males are instead called "capons". Females, on the other hand, are referred to as "hens" once they reach adulthood and "pullets" while still immature.
Humans have interacted with chickens for thousands of years primarily as a source of sustenance or for their companionship. From ancient India, the chicken spread to the Middle East and Europe before becoming globalized as a result of colonialism and international trade. Today, chickens are one of the most numerous domestic animals in the world, with a population of 23.7 billion in 2018. Broilers are a type of chicken raised specifically for meat consumption, while layers are used for egg production.
Chicken-related references can be found in multiple cultural artifacts spanning myth, folklore, religion, and literature, emphasizing the animal's significance throughout history. Genetic studies have revealed different maternal origins of chickens within South Asia, Southeast Asia, and East Asia; however, the clade found in the Americas, Europe, the Middle East, and Africa originated from the Indian subcontinent. The chicken is known to have appeared in ancient Egypt and Greece, with mentions dating as far back as the mid-15th century BC.
Terminology
The adult male of domestic chickens is called a rooster or cock, while the adult female is referred to as a hen. biddy, capon, chick, chook, cockerel, Dunghill fowl, pullet, yardbird. Commonly, chicken may also refer to a young bird. In scientific and trade circles, common fowl or domestic fowl are terms used for this species. In Australian vernacular English, the term "chook" is commonly used to refer to the chicken species. The word "chick" is rarely used to mean chicken but mainly on Merriam-Webster's "Sense 1b" which refers to the young of any bird.
Other terms include:
Biddy: a recently-hatched chicken.
Capon: a male chicken that has been castrated or neutered.
Chick: a juvenile chicken, typically one that is still fluffy and unable to fly.
Cockerel: a juvenile male chicken that has yet to reach one year of age, often referred to as a rooster in North America.
Dunghill fowl: a hybrid chicken that is derived from a combination of various domestic chicken breeds. Pullet: a juvenile female chicken that has not yet reached sexual maturity and is less than 22 weeks old in the poultry industry.
Yardbird: a chicken (southern United States, dialectal)
Chook: a chicken (Australia/New Zealand, informal)
Chicken was initially used to describe immature or young birds. In current trade and scientific contexts, the species is known as common fowl or domestic fowl. In Australian vernacular English, "chook" is a common term employed for hens, with "chick" predominantly referring to any bird's young.
Etymology
As per Merriam-Webster's dictionary, the term "rooster" emerged in the mid- to late-18th century, serving as a delicate substitute to sidestep the amorous undertones associated with the original English word, "cock". This linguistic evolution sought to provide a more socially acceptable alternative, and it has gained widespread usage across North America. Notably, a rooster pertains to a male bird that engages in the act of roosting, which involves finding a high perch to rest upon during the nocturnal hours.
Definition | Physical Description and Size of Chickens
Biology and habitat
Chickens are omnivorous bird species that frequently root through soil in search of seeds, insects, and the occasional small lizard, snake, or mouse. Depending on their breed, they can live for 5-10 years on average, with the oldest recorded chicken in the world living up to 16 years in accordance with Guinness World Records.
Typically identified by their vibrant plumage of lengthy, flowing tails and shiny, pointed feathers on their neck and backs (known as hackles and saddles), roosters can be distinguished from hens. As a notable exception, breeds such as the Sebright chicken have slightly pointed neck feathers that match a hen's coloration. Identification can be made by examining the comb or the eventual development of spurs on the male's legs. Certain hybrids and breeds have variations in chick coloration between male and female.
Both adult male and female chickens bear clusters of fleshy protuberances on the head and throat, known as caruncles. Prominence of these and wattles is generally greater among males. They can also have a muff or beard, an extra feathering mutation found in several chicken breeds that creates a facial downy appearance.
Although lighter breeds are capable of short-distance flights, domesticated chickens generally cannot perform long-distance flight, with occasional, brief flights made to evade perceived danger.
A cock, with its comb shown.
Comb of a hen.
A chick.
Behavior
Social behavior
Chickens are social birds that thrive in group settings, demonstrating communal behaviors when it comes to caring for young and incubating eggs. Flock members naturally establish a pecking order to determine food access and nesting locations, with dominant individuals taking priority. The removal of hens or roosters from a flock will temporarily disrupt the social order until a new pecking order is established. When adding hens to an existing flock, particularly younger ones, fighting and injury may occur. Additionally, when feeling threatened or unwell, a chicken may puff up its feathers.
A hen with chicks.
Vocalizations
The rooster is known to exhibit specific behaviors, such as clucking in a high pitch and picking up and dropping food to get other chickens to eat. This behavior can also be observed in mother hens who encourage their chicks to eat. Roosters use their loud crow as a territorial signal to other roosters. However, they may also crow in response to sudden disturbances in their surroundings. Loud clucking is typical for hens after laying eggs and when calling their chicks. Moreover, chickens vocalize different warning calls when they sense predators approaching by air or on the ground.
Crowing
A crowing rooster.
Roosters are known to start crowing prior to being four months old. While hens are also known to crow, the development of hackles and crowing are clear indicators of a rooster. Rooster crowing contests are traditional sports held in countries including the United States, Belgium, Japan, Indonesia, Germany, and the Netherlands. When it comes to longcrowers, which are often used in these contests, the duration or frequency of crowing is measured based on the breed.
Courtship
In order to initiate courting, male chickens (roosters) may perform a circle dance around or near a hen, regularly extending the wing that is closest to the hen. This dance elicits a response in the hen, and when she responds to his call, the rooster may mount the hen and proceed with mating. Specifically, mating typically includes the following sequence of behaviors: male approach, male pre-copulatory waltzing, male waltzing, female crouching in receptive posture or stepping aside or running away if unwilling to copulate, male mounting, male treading with both feet on the hen's back and, finally, male tail bending following successful copulation.
Nesting and laying behaviour
In the world of hens, it is not uncommon for them to lay eggs in nests already containing eggs and even relocate eggs from neighboring nests to their own. These actions lead flocks to utilize only a few preferred locations, as opposed to one nest for every bird, and hens often display a preference to lay in the same spot. In some circumstances, two or more hens will attempt to share a single nest, possibly resulting in chickens laying on top of one another if the nest proves too small or if one of the hens is particularly tenacious. On the topic of nesting habits, research has demonstrated that individual hens tend to favor either solitary or communal nesting behaviors.
Broodiness
Under typical circumstances, most bird species cease laying eggs when a clutch is complete. At this stage, the incubation of eggs commences, and hens, in particular, become broody. Broody hens will sit on the nest, often fluffing up their feathers or pecking to protect their eggs. They usually do not leave the nest to eat, drink, or dust-bathe, instead concentrating on egg incubation. Maintaining a constant temperature, humidity and regular egg turning during incubation are vital, and to induce broodiness, several artificial eggs may be placed in the nest. Conversely, the hen can be placed in a raised cage with an open wire floor to discourage broodiness.
Hens specifically bred for production of eggs tend to rarely go broody. Those that do might stop midway through incubation. On the other hand, other breeds like the Cochin, Cornish, and Silkie regularly become broody and are exceptional mothers not just to chicken eggs but also to those of other species, including quail, pheasants, ducks, turkeys, or geese, regardless of the eggs' size or incubation period.
Hatching and early life
Chicken eggs that are fertile will hatch approximately 21 days after the start of incubation. Even if laid over a period of two weeks, the chicks will hatch within a day or two of each other, due to development starting only when incubation begins. Prior to hatching, hens are able to hear chicks peeping inside their eggs and will cluck gently to coax them out of their shells. Once hatched, chicks absorb the remaining egg yolk and withdraw blood supply from the shell membrane. They then break free by severing the blunt end of the shell and drying in the warmth of their nests. For several days after hatching, newborn chicks feed from an internal yolk sac and are fiercely protected by their mothers. As they grow, hens will lead chicks to food and water and care for them until they are several weeks old. Some chicken breeds have been known to develop a habit of eating cracked eggs.
Reproduction
The transfer of sperm occurs through cloacal contact between the male and female, which is often referred to as the 'cloacal kiss'. Similar to other birds, reproduction is regulated by a neuroendocrine system, particularly by the Gonadotropin-Releasing Hormone-I neurons located in the hypothalamus. Reproductive hormones, such as estrogen, progesterone, gonadotropins (luteinizing hormone and follicle-stimulating hormone) function locally to the reproductive system, instigating and sustaining sexual maturation changes. The reproductive system experiences diminished activity with time, which is thought to be associated with GnRH-I-N decline. Notably, owing to significant inter-individual variability in egg-producing duration, it is believed possible to breed for a further prolonged useful lifetime in egg-layers.
Embryology
Chicken embryos have been extensively used as model organisms for studying the development process. Commercial chicken farmers who sell fertilized eggs can provide a large number of embryos that can be easily observed. Embryologists can perform experiments on these embryos, reseal the egg, and study the effect later, thus making it a crucial tool for discovering how limbs develop, including the discovery of the apical ectodermal ridge and the zone of polarizing activity by John W. Saunders. In 2006, scientists studying the ancestry of birds, by activating a chicken recessive gene known as talpid2, found that the embryo jaws initiated the formation of teeth, resembling those found in fossils of ancient birds.
Genetics and genomics
The chicken is a central figure in agriculture and meat production, as well as scientific research. It was the first bird genome to be sequenced, with a genome size of 1.21 Gb, which is significantly smaller than larger vertebrate genomes, such as the human genome (3 Gb). The final gene set included 26,640 genes, some of which were noncoding genes and pseudogenes, and annotation release 103 (2017) identified a total of 19,119 protein-coding genes, similar to that of the human genome.
Physiology
Chickens originating from lofty terrains, such as Tibet, exhibit remarkable physiological adaptations that confer upon them a heightened capacity for hatching in oxygen-deprived environments. In the presence of low oxygen conditions, embryos from these particular chicken populations showcase a substantial upregulation of hemoglobin expression compared to their counterparts from different populations. Intriguingly, the hemoglobin produced in these embryos displays an enhanced affinity for oxygen, facilitating a more efficient binding of oxygen molecules.
Initially detected within the pineal gland of chickens, pinopsins represent a noteworthy discovery.
While it is noteworthy that all avian species seem to lack TLR9, Taghavi et al. in 2008 successfully elicited artificial immunity against bacterial pathogens in neonatal chicks by employing customized oligodeoxynucleotides. This achievement offers intriguing possibilities for immunization strategies in the avian realm.
Origin and dispersal
Origin
Galliformes, the avian order to which chickens belong, played a pivotal role in the survival of birds amidst the mass extinction event that eradicated their arboreal counterparts and the dinosaurs. These resilient creatures, encompassing waterfowl and ground-dwelling species akin to present-day partridges, managed to endure the Cretaceous-Paleogene extinction, securing their place in the evolutionary timeline.
From this resilient lineage emerged the modern galliformes, of which domesticated chickens serve as a prominent example. Primarily descended from the red junglefowl (Gallus gallus), they are scientifically classified as belonging to the same species. As a result, domestic chickens have the innate capability to interbreed freely with populations of their wild ancestors, the red junglefowl.
Over time, hybridization occurred between domestic chickens and other junglefowl species, including the grey junglefowl, Sri Lankan junglefowl, and green junglefowl.[54] Through this interbreeding, certain traits were introduced into the domestic chicken genome. For instance, the gene responsible for yellow skin pigmentation was incorporated into domestic birds through hybridization with the grey junglefowl (G. sonneratii).
A comprehensive study conducted in 2020 shed light on the genetic connections between chickens and their wild counterparts. It was discovered that chickens share approximately 71% to 79% of their genome with the red junglefowl. Moreover, the process of domestication can be traced back approximately 8,000 years, marking a significant milestone in the human-chicken relationship.
Domestication
In an early study, it was proposed that the modern chicken, with its diverse breeds, can be traced back to a singular domestication event involving the red junglefowl in what is now Thailand. Minor transitions occurred along the way, leading to the variations we see today. The red junglefowl possesses advantageous adaptations that allow it to capitalize on the abundant seed resources available during the cyclical bamboo seeding phase, thereby promoting its own reproductive success. Humans, in their endeavor to domesticate chickens, capitalized on this innate inclination of the red junglefowl to reproduce prolifically when provided with ample food resources.
The precise time and location of chicken domestication continue to be subjects of debate. Genomic investigations indicate that approximately 8,000 years ago, the process of domestication commenced in Southeast Asia, subsequently spreading to China and India 2,000 to 3,000 years later. Archeological evidence supports the presence of domestic chickens in Southeast Asia prior to 6000 BC, in China by 6000 BC, and in India by 2000 BC. A groundbreaking study published in Nature in 2020, which involved the complete sequencing of 863 chickens worldwide, proposes that all domestic chickens originated from a singular domestication event involving the red junglefowl. The modern distribution of this wild ancestor is primarily found in southwestern China, northern Thailand, and Myanmar. As domesticated chickens spread across Southeast and South Asia, they interbred with local wild species of junglefowl, resulting in distinct genetic and geographical groupings. Notably, an analysis of the widely popular White Leghorn breed revealed a complex mixture of ancestral contributions inherited from different subspecies of the red junglefowl.
Dispersal
The existence of a term for the domestic chicken (*manuk) within the reconstructed Proto-Austronesian language indicates that these birds have been domesticated by the Austronesian peoples since ancient times. Accompanied by dogs and pigs, chickens accompanied the prehistoric Austronesian maritime migrations, spanning from Taiwan and extending to Island Southeast Asia, Micronesia, Island Melanesia, Polynesia, and Madagascar, commencing around 3000 BC. While there is a possibility that these chickens were introduced to South America by Polynesian seafarers during pre-Columbian times, conclusive evidence for such claims remains speculative.
In the Middle East, chicken remains have been traced back to slightly before 2000 BC in Syria. They were introduced to Egypt around 1400 BC for the purposes of cockfighting and gained widespread breeding popularity in the region by 300 BC. Phoenician traders carried chickens along the Mediterranean coasts, extending their reach as far as Iberia. During the Hellenistic period (4th-2nd centuries BC), in the southern Levant, chickens began to be extensively domesticated for food, preceding the spread of chicken domestication to Europe by at least a century.
The earliest depictions of chickens in Europe can be found on Corinthian pottery dating back to the 7th century BC. Chickens reached Europe around 100 BC, experiencing increased breeding practices under the Roman Empire but diminishing in importance during the Middle Ages. Genetic analysis of chicken bones from archaeological sites in Europe revealed that during the High Middle Ages, chickens exhibited reduced aggression and began laying eggs earlier in the breeding season.
The introduction of chickens into Africa during the early first millennium AD is believed to have occurred through multiple possible routes, including the Egyptian Nile Valley, the Roman-Greek or Indian trade with East Africa, or via Carthage and the Berbers crossing the Sahara. The earliest known chicken remains in Africa have been discovered in Mali, Nubia, the East Coast, and South Africa, dating back to the middle of the first millennium AD.
The history of domestic chickens in the Americas prior to Western contact remains a topic of ongoing discussion. However, the presence of blue-egged chickens, found exclusively in the Americas and Asia, suggests an Asian origin for early American chickens. Limited data from Thailand, Russia, the Indian subcontinent, Southeast Asia, and Sub-Saharan Africa poses challenges in mapping the precise spread of chickens in these regions. Further research incorporating comprehensive descriptions and genetic analysis of local chicken breeds at risk of extinction may provide valuable insights in this regard.
South America
The Araucana, an intriguing chicken variety originating from South America, holds a distinct place in poultry history. Bred in southern Chile by the Mapuche people, Araucanas possess the remarkable ability to lay eggs in shades of blue and green. Adding to their uniqueness, certain individuals within the Araucana breed lack tails, while others exhibit striking tufts of feathers around their ears. These distinct characteristics have fueled speculation regarding the Araucanas' ancestry, suggesting that they existed prior to the arrival of European chickens brought by the Spanish. Some researchers propose that the presence of Araucanas is evidence of pre-Columbian trans-Pacific connections between Asian or Pacific Oceanic peoples, particularly the Polynesians, and South America.
In 2007, an international team of researchers conducted a comprehensive analysis of chicken bones discovered on the Arauco Peninsula in south-central Chile. The results shed new light on the origins of these unique chickens. Radiocarbon dating of the bones indicated their pre-Columbian age, further bolstering the hypothesis of their antiquity. Moreover, DNA analysis revealed a genetic relationship between these chickens and ancient populations of chickens in Polynesia, providing substantial support for the notion that the Araucanas originated from Polynesia and substantiating the existence of transpacific interactions between Polynesia and South America prior to the arrival of Christopher Columbus in the Americas.
Human utilization of chickens
Farming
Annual Rearing of Chickens for Human Consumption
The global scale of chicken production is staggering, with over 50 billion chickens raised each year to meet the demand for meat and eggs. In the United States alone, the numbers are astounding, as more than 8 billion chickens are slaughtered annually for their meat, while over 300 million chickens are specifically reared for egg production. However, it is important to note that the majority of poultry is raised in factory farms, a practice that has become prevalent worldwide. According to the Worldwatch Institute, a significant 74% of the world's poultry meat and 68% of eggs are derived from these industrialized systems. Nevertheless, an alternative approach gaining momentum is free-range farming, which offers a different paradigm for poultry production.
The clash between these two primary methods, namely intensive farming and free-range farming, has sparked ongoing debates and raised concerns about ethical consumerism. Detractors of intensive farming emphasize its detrimental impact on the environment, the associated human health risks, and the perceived inhumane treatment of animals. On the other side of the spectrum, proponents of intensive farming argue that their highly efficient systems actually contribute to saving land and food resources due to increased productivity. Additionally, they claim that animals are cared for within state-of-the-art environmentally controlled facilities.
The complex dynamics and inherent trade-offs between these contrasting approaches highlight the need for ongoing discussions and considerations surrounding the ethical, environmental, and health aspects of poultry farming.
Raised for Meat: Broilers and Their Growth
Within the realm of poultry farming, chickens specifically raised for meat production are commonly referred to as broilers. While chickens naturally have a lifespan of six years or more, broiler breeds have been selectively bred to reach their slaughter size in less than six weeks. This accelerated growth rate allows for efficient production in commercial settings.
It is worth noting that broilers reared under free-range or organic conditions follow a different timeline. These birds are typically given more time to mature and develop, with slaughter typically taking place around 14 weeks of age. This extended period allows for a more natural growth pattern, aligning with principles of ethical and sustainable farming practices.
Egg Production
Chickens specifically bred for egg production are commonly known as layer hens. Their role in providing the world with a steady supply of eggs is significant, with the United Kingdom alone consuming over 34 million eggs on a daily basis. Certain breeds of hens have the remarkable ability to produce over 300 eggs per year, with the highest authenticated rate recorded at 371 eggs in 364 days.
However, after approximately 12 months of continuous laying, the commercial viability of the flock begins to decline. The egg-laying capacity of hens diminishes, rendering them economically unfeasible for continued egg production. In battery cage systems, these hens may experience various health issues and suffer feather loss, resulting in a reduced life expectancy of less than two years, as opposed to their potential lifespan of around seven years.
In the United Kingdom and Europe, laying hens that have reached this stage are typically slaughtered and utilized in processed food products or sold as "soup hens". In certain countries, an alternative approach called force molting is employed to reinvigorate egg-laying capabilities instead of immediate slaughter. Force molting entails the complete withdrawal of food, and sometimes water, for a period ranging from 7 to 14 days, causing the hen to experience a body weight loss of 25% to 35% or even up to 28 days under experimental conditions. This process prompts the hen to shed her feathers while stimulating renewed egg production. Some flocks may undergo force molting multiple times, and in the United States, over 75% of all flocks were subjected to this practice in 2003.
The intricate journey of layer hens highlights the complexities and considerations involved in egg production, with factors such as lifespan, welfare, and industry practices influencing the course of their lives.
A commercial poultry farm.
Chickens as Pets
A young girl with her pet chickens.
In recent years, keeping chickens as pets has witnessed a significant surge in popularity, particularly among urban and suburban residents. What was once predominantly a practice for rural environments has now become a trend embraced by individuals seeking the joys of pet ownership. While chickens are primarily valued for their egg-laying abilities, they are increasingly being treated as cherished companions, much like cats or dogs.
One of the remarkable aspects of having chickens as pets is the bond that forms between humans and these feathered friends. Owners often assign names to their chickens and develop a personal connection with them. Although cuddling may not be their preferred form of affection, chickens readily eat from their owner's hand and can even perch on their lap. They demonstrate responsiveness and follow their handlers, showcasing their unique personalities and offering a sense of companionship.
Chickens possess intriguing social dynamics and exhibit inquisitiveness and intelligence. Observing their behavior can be genuinely captivating, providing entertainment and amusement for their owners. Certain breeds, such as silkies and various bantam varieties, are known for their docility, making them particularly suitable as pets, especially for children with disabilities who can benefit from their gentle nature.
In addition to their endearing qualities, chickens often become recipients of kitchen food scraps, further solidifying their position as valued members of the family. This practice not only helps reduce food waste but also establishes a sustainable and eco-friendly approach to their care.
A group of chickens eating corn and food scraps.
The growing popularity of chickens as pets reflects the increasing recognition of their unique attributes and their potential to enrich the lives of their human companions. As more individuals embrace the joys of keeping chickens as household pets, the bond between humans and these remarkable birds continues to deepen.
Diseases and ailments
The realm of poultry farming is not exempt from the threats posed by various diseases, parasites, and ailments that afflict chickens. These resilient creatures encounter adversaries in the form of lice, mites, ticks, fleas, and intestinal worms. Additionally, they face the risk of contracting several diseases. However, it is important to note that chickens, despite their name, are not susceptible to chickenpox, as this particular ailment is generally confined to humans.
One notable concern is the potential for chickens to carry and transmit salmonella through their dander and feces. In the United States, the Centers for Disease Control and Prevention (CDC) strongly advise against allowing chickens indoors or permitting small children to handle them. The risk of salmonella infection underscores the importance of responsible handling and hygiene practices to minimize the potential for disease transmission within both human and poultry populations.
By acknowledging and addressing these disease risks, poultry farmers and enthusiasts can take proactive measures to safeguard the health and well-being of their flocks while promoting the overall safety and welfare of the community.
Below is a compilation of several diseases that affect chickens.
Name
Common name
Cause
Aspergillosis
Aspergillus fungi
Avian influenza
bird flu
virus
Histomoniasis
blackhead disease
Histomonas meleagridis
Botulism
paralysis
Clostridium botulinum toxin
Cage layer fatigue
mineral deficiency, lack of physical exercise
Campylobacteriosis
tissue injury in the gut
Coccidiosis
Coccidia
Colds
virus
Crop bound
improper feeding
Dermanyssus gallinae
red mite
parasite
Egg binding
oversized egg
Erysipelas
Streptococcus bacteria
Fatty liver hemorrhagic syndrome
high-energy food
Fowl cholera
Pasteurella multocida
Fowlpox
Fowlpox virus
Fowl typhoid
bacteria
Avian infectious laryngotracheitis
LT
Gallid alphaherpesvirus 1
Gapeworm
Syngamus trachea
worms
Infectious bronchitis
Infectious bronchitis virus
Infectious bursal disease
Gumboro
infectious bursal disease virus
Infectious coryza in chickens
Avibacterium paragallinarum
Lymphoid leukosis
Avian sarcoma leukosis virus
Marek's disease
Gallid alphaherpesvirus 2
Moniliasis
yeast infection or thrush
Candida fungi
Mycoplasma
bacteria
Newcastle disease
Avian avulavirus 1
Necrotic enteritis
bacteria
Omphalitis
Mushy chick disease
bacteria
Peritonitis
infection in abdomen from egg yolk
Psittacosis
Chlamydia psittaci
Pullorum
Salmonella
bacteria
Scaly leg
Knemidokoptes mutans
Squamous cell carcinoma
cancer
Tibial dyschondroplasia
speed growing
Toxoplasmosis
Toxoplasma gondii
Ulcerative enteritis
bacteria
Ulcerative pododermatitis
bumblefoot
bacteria
The Science and Precision of Artificial Incubation of Chickens
Artificial incubation offers a controlled and optimized environment for the development of chicks, utilizing advanced machinery for this purpose. The average incubation period for chickens spans 21 days, although the specific duration relies on the precise temperature and humidity settings within the incubator. Temperature regulation stands as the paramount factor for a successful hatch, with variations of more than 1 °C (1.8 °F) from the optimal temperature of 37.5 °C (99.5 °F) having detrimental effects on hatch rates. Humidity also plays a pivotal role, as the rate of water evaporation from the eggs is influenced by the ambient relative humidity. The evaluation of evaporation can be achieved through candling, a process that allows for the assessment of the air sac's size, or by monitoring weight loss. During the last three days of incubation, relative humidity should be increased to approximately 70% to prevent the delicate membrane surrounding the hatching chick from drying out once the shell is cracked. Lower humidity levels are maintained during the initial 18 days to facilitate proper evaporation.
The positioning of eggs within the incubator significantly impacts hatch rates. To maximize success, eggs should be positioned with their pointed ends facing downward and should be regularly rotated (at least three times per day) until approximately one to three days prior to hatching. Neglecting to turn the eggs may result in the developing embryo adhering to the shell, leading to potential physical deformities upon hatching. Adequate ventilation is crucial to ensure a continuous supply of oxygen to the developing embryo. As eggs age, increased ventilation becomes imperative.
In the realm of commercial poultry production, industrial-scale incubators take center stage, boasting shelves capable of accommodating tens of thousands of eggs simultaneously, with the entire process of egg rotation being fully automated. Conversely, home incubators, designed for smaller-scale operations, offer compartments that can house anywhere from 6 to 75 eggs, providing enthusiasts with the means to engage in the fascinating process of incubation within the comfort of their own settings.
