The life of a laying hen

Natural life and the intelligence of the chicken

The modern domesticated chicken has evolved over thousands of years of selective breeding. Its wild ancestor is the Junglefowl (Gallus gallus), from which the chicken originated around 8,000 years ago. The Junglefowl, also known as the Red Junglefowl, is a tropical member of the pheasant family and is roughly the size of a bantam chicken. Found in the dense forests of India and Southeast Asia, the Junglefowl's vibrant feathers offer excellent camouflage among the red and brown leaves on the forest floor. While they can fly short distances, they mainly move on foot and prefer areas with dense vegetation for shelter and safety. Junglefowl are most active in the early morning, rest during the day, and become lively again in the late afternoon until dusk. Roosters crow at dawn to define their territory and establish their social ranking. In India, Junglefowl typically live in groups averaging 5 individuals, and their habitat spans about 50 hectares^[1].

The modern chicken

Despite notable physiological differences, laying hens display behaviors akin to those of the Junglefowl, particularly when domesticated chickens are permitted to act naturally. When domesticated chickens are released into the wild, they tend to show behaviors very similar to those of Red Junglefowl^[2]. Chickens possess a complex social structure. A flock typically comprises 4 to 30 individuals, usually featuring one dominant rooster alongside subordinate hens and roosters. The flock often roosts together in the same tree. The dominant rooster defends his territory but allows subordinate roosters to remain. He chases these roosters to the edges of his territory once they reach maturity. Hens also establish a pecking order, which is generally more stable than that of roosters. To ascertain the hierarchical position of a flock member, hens recognize each other's heads. Chickens can individually identify up to approximately 100 of their own species. Roosters communicate their status by crowing. Additionally, chickens observe the actions of other flock members to gauge the status of unfamiliar (stranger) chickens. Beyond hierarchical relationships, hens, in particular, form friendships with one another. This helps reduce stress and strengthens social bonds.

In natural conditions, a mother hen leaves the flock as soon as she is ready to lay her eggs. She remains on the nest for three weeks, leaving only briefly once a day to eat and drink. Although the embryos are still developing, they can already communicate with their mother using "clicking" sounds and beak clapping, which encourages her to return to the nest. If an embryo becomes too cold, it also makes a sound, prompting the hen to move the egg closer to her body. The embryo then produces a different sound to indicate that it is now warm. Because a chick communicates with its mother while still in the egg, it recognizes her call as soon as it hatches. The newly hatched chick begins to explore its surroundings and pecks at spherical objects. A hen teaches her chicks what is edible by calling and pecking at the ground. If the chicks peck at inedible items, their mother corrects them by intensively demonstrating the right behavior. For the first four days, the chicks stay close to their mother, which keeps them warm and safe. When it rains, the chicks take shelter under the hen's wings. The chicks learn from their mother how to take dust baths and roost. The hen also instructs the chicks on how to respond to danger. She has over 30 different sounds, which she uses to signal danger and whether it originates from the air or the ground. The chicks also learn from one another through play, which likely helps them understand how to react to aggression. As they grow older, the chicks venture further away from their mother. After six weeks, they can walk up to 20 meters away. At this age, the chicks also begin to establish a hierarchy. Dominance is determined through hopping (jumping towards something), threatening (standing upright with their head above another), jumping, kicking, and aggressive pecking. After eight to ten weeks, the chicks start foraging for food independently, but they still remain close to their mother and siblings. By eighteen weeks, the chicks integrate with the rest of the flock. Under natural conditions, chickens follow a consistent pattern of behavior that closely resembles that of their wild relative, the Junglefowl. In the morning, they search for food, around noon they take dust baths, and in the afternoon they groom their feathers. They may also take short naps in between. At the end of the afternoon, around dusk, they embark on a second foraging expedition. When night falls, they roost together. In the wild, chickens spend most of their active hours foraging for food and exploring their environment. Even when food is abundant, they continue to search for potentially better options. Interestingly, chickens can sleep and remain awake simultaneously. Because one eye is connected to one hemisphere of their brain and the other to the opposite hemisphere, they can sleep with one eye open, allowing them to stay vigilant against predators and other threats. In this phenomenon known as "unihemispheric slow-wave sleep" (USWS), only one hemisphere of the brain is asleep.^[3]

As intelligent as dogs and primates?

Research indicates that chickens are far more intelligent than commonly believed. For instance, newborn chicks possess a numerical sense that allows them to recognize quantities up to 10. They can differentiate between a hole containing food and 10 other holes.^[4]. In addition to their numerical skills, they also grasp geometric concepts. Chicks can complete the shape of an incomplete triangle and choose the correct 3D representation from various 2D images of a cube.^[5]. Beyond their impressive spatial awareness, chickens have a sense of time and can anticipate future events. For example, researchers trained chickens to peck at a touchscreen for several minutes, which resulted in them receiving more food than if they had pecked at the food immediately^[6].

Chickens' ability to comprehend object permanence is remarkable. This means they understand that an object still exists even when it is no longer visible, such as when it has been removed. Human infants typically develop this understanding after 6 to 7 months. Young chicks have been observed remembering an object they saw through a small window and can locate it by navigating around obstacles^[7]. Another impressive trait of chickens is their vision. Chickens possess 5 types of cones, while humans have only 3. This enables them to perceive UV light, which is invisible to humans. Consequently, they can see the sunrise an hour earlier than we do. Chickens' brains are structured similarly to human brains^[8]. Areas responsible for cognitive functions, such as long-term memory and problem-solving abilities, exhibit significant similarities. In many ways, chickens' cognitive skills surpass those of dogs, cats, and even some primates. Emotionally, chickens also share similarities with humans. Chickens, like humans, can experience empathy towards their peers. For instance, hens respond strongly when their chicks or other chickens are stressed.^[9]. Chickens also express emotions such as sadness, fear, anxiety, enthusiasm, frustration, friendship, and boredom^[10]. Moreover, chickens can deceive others for their own benefit. For example, subordinate roosters, who typically cannot mate with hens in the flock, attract hens by pretending to have food, allowing them to breed regardless.^[11]. We can conclude that chickens are social and intelligent beings, not as different from us as we might think.

Organization of the modern egg industry

For centuries, chickens roamed freely in yards and were raised for both eggs and meat. After the Second World War, a clear distinction developed between laying hens, which are kept for eggs, and broiler chickens, which are raised for meat production. Laying breeds are specifically bred to maximize egg production, while broiler breeds are bred for rapid growth (the well-known "broiler chicken"). In 2016, there were over 46 million laying hens in the Netherlands^[14]. Since 2004, the average number of laying hens per farm has been increasing, reaching 40,698 laying hens per farm in 2016^[15]. In total, there were 920 laying hen farms (36.5 million laying hens) and 150 so-called rearing farms (9.5 million laying hens) in 2016^[14]. Approximately two-thirds of these farms are located in the provinces of Gelderland, North Brabant, and Limburg. The 36.5 million laying hens produce around 11 billion eggs for consumption each year.

Hybrids

In modern poultry farming, farmers use hybrids, which are crossbreeds of different chicken breeds. These hybrids are created to boost egg production through the "heterosis effect." This effect means that the hybrid chicken performs better than the average of its parent breeds. The greatest benefits come from crossing very different breeds.

However, the genetic advantages of heterosis do not pass on effectively to the next generation. As a result, the benefits diminish with each generation. To maintain the maximum heterosis effect and achieve the highest egg production, breeders continually cross pure breeds (lines) to create new hybrids.

This intense focus on high egg production has consequences. Hybrids tend to wear out more quickly because the demands of laying so many eggs take a toll on their health. They produce more fragile eggs and often have poorer plumage.

Great-grandparent, grandparents and parents

As mentioned earlier, laying hens are hybrids derived from pure breeds. These pure breed lines serve as the great-grandparents and grandparents of the hybrids. When two different pure lines, A and B, are crossed, they create hybrids. In this case, the great-grandparents, grandparents, and parents are the pure lines A and B (Figure 1). The crossing of the parent stock results in a hybrid known as AB. This hybrid, made from purebred lines A and B, represents the ultimate laying hen.

Three major players control these purebred lines and cross them to produce hybrids. The two largest are the Dutch Hendrix Genetics, which includes the Isa, Babcock, Shaver, Hisex, Bovans, and DeKalb lines, and the German EW group, which features the Lohmann, Hy-line, and H&N lines. The third player is the French Grimaud group, known for the Novogen line. These companies also typically control the breeding operations that supply the ultimate parent stock. The hybrids are marketed under names like DeKalb white for white laying hens and Isa brown for brown laying hens.

Propagation

In the Netherlands, there are around 40 breeding farms where parent stock is grouped together to lay fertilized eggs. Typically, there is one rooster for every eight hens. The breeding supply chain is dominated by a few large companies. For instance, ISACOM, which is part of Hendrix, operates 10 breeding farms and sources its parent stock from ISA, the laying hen division of Hendrix Genetics.

Dubbing

The combs of white breed chickens are clipped without anesthesia when they are still chicks. This procedure is known as comb dubbing. Research shows a positive correlation between comb size and egg production as well as egg weight. This indicates that birds with smaller combs tend to lay fewer and smaller eggs.^[16]. In other words, the large combs are a result of selective breeding aimed at maximizing egg production. In brown breeds, the combs are much smaller, and this is not a concern. Consequently, dubbing the combs of brown breed roosters has been legally prohibited since 2015. However, in white breed roosters, the comb can grow so large that it obstructs their vision, making it difficult for them to mate and even to feed. Dubbing the comb is also used to identify sex errors. While research from WUR in 2011 indicates that there is no serious discomfort during comb clipping, "mild" discomfort cannot be completely ruled out since only externally observable parameters were studied.^[17].

Hatchery

The fertilized eggs, referred to as hatching eggs, are transported to a hatchery, where they are artificially incubated in an incubator. Chicks typically hatch between 19 and 22 days old, but for economic efficiency, the incubator is opened and emptied only once. This usually occurs on day 21, when most of the eggs have hatched. The chicks are then immediately sexed; this process involves separating the male and female chicks. The male chicks are promptly gassed or ground up alive, as they are economically worthless. Male chicks do not lay eggs and are also unsuitable for meat production due to their slower growth rate. This results in approximately 45 million "useless" male chicks being culled annually.^[18] In hens, the tip of the beak is often immediately burned off using infrared radiation to prevent feather pecking. This is a very sensitive and painful procedure, as many nerves are concentrated in this area.^[16] The newborn chicks also receive their first vaccinations. Afterward, the day-old chicks are transported to the rearing farm. The term "day-old chick" is actually misleading, as some chicks may already be two days old when the incubator is emptied. Hatched chicks still have enough nutrients in their egg yolk for about 72 hours, but they do not receive their first feed until after being transported to the rearing farm. This process takes 32 to 48 hours after the incubator is emptied. Consequently, chicks that hatch first may sometimes go without food for up to 96 hours, effectively "going hungry" for a day.^[19]

Ready to lay

For the first 16 to 18 weeks, chickens live on a rearing farm. During this time, they get most of their vaccinations against common diseases. In total, they receive over 20 vaccinations for about 14 different diseases. Only the Newcastle Disease (NCD) vaccination is legally required. Organic laying hens also get these vaccinations. As laying hens produce more eggs, the vaccination costs per egg decrease, leading to a trend of increasing vaccinations. After this rearing period, the laying hens move to enriched cages or a free-range barn and start laying eggs at 19 weeks.

Egg production

A barn typically houses a single laying flock, which is a group of hens of the same age that are purchased together from a rearing farm. This setup allows for the quick filling of an empty barn and facilitates the process of emptying the barn when the laying hens are no longer producing enough eggs and are sent to the slaughterhouse. This practice enables thorough cleaning and disinfection of the barn, which is crucial due to the presence of numerous pathogens. After cleaning, a new laying flock can move into the barn. During their peak laying period, from 25 to 39 weeks of age, hens produce 6 to 7 eggs per week. Through selective breeding and the use of artificial light to extend the day length, laying hens can lay eggs throughout the year. The light duration is maintained at 14 to 16 hours, while the dark period ("night") lasts 8 to 10 hours. A continuous dark period of at least 8 hours is legally mandated.^[20] After about 50 weeks of laying, mortality rates increase (laying hens may become ill or die) due to wear and tear, decreased resistance, and/or exhaustion, potentially reaching 8%.^[21] After 60 to 70 weeks, egg production also declines, and in most instances, the hens are sent to the slaughterhouse because they are no longer economically viable. Occasionally, hens are kept for a second laying cycle. Typically, chickens molt (the process of replacing worn feathers) naturally each year, which can take several months. However, due to selective breeding and the artificial conditions in barns, the time before molting is extended from one year to over a year and a half. For a second laying cycle, hens must first molt before they can begin laying eggs again. To ensure this process happens uniformly and quickly, hen keepers induce molting by providing low light and less and/or leaner food for three to seven weeks. Notably, the second laying cycle is shorter than the first, and hens lay 10 to 30% fewer eggs than during the first cycle.^[23] Therefore, in practice, laying hens are seldom kept for a second laying cycle. For instance, forced molting is not allowed for the Beter Leven quality mark. Laying hens typically live for about 19 to 21 months, or at most 31 months for a second laying cycle. By that time, they will have laid over 300 eggs, and this number continues to rise. Hendrix Genetics, for example, anticipates that 500 eggs per laying hen should be achievable by 2020.^[24] In comparison, wild chickens lay about 10 to 20 eggs per year (Fig. 2). Through selective breeding and the use of artificial light to extend daylight hours, this figure has increased significantly. For instance, at the end of the 19th century, chickens laid 80 to 85 eggs per year, and by 1930, that number had already risen to 116. This figure has now tripled. ISA has bred a hen that laid 577 eggs in 588 days.^[24]

The productive lifespan is also expected to be extended further. It is projected that within 10 years, laying hens will be able to be kept for a hundred weeks, or nearly two years, before they are considered "deprecated." Interestingly, there is no significant difference in the "lifespan" of hens across various housing systems. Even organic, Kipster, or Rondeel hens do not live longer than a year and a half. The average lifespan of chickens varies greatly by breed. Hybrids often do not exceed three years, while some breeds can live up to 20 years. Most purebred chickens live around 10 years (Fig. 3).

Since laying hens are completely "used up" by the time they are captured and sent to the slaughterhouse, they are only suitable for low-value applications. In other words, they are processed into soup, chicken nuggets, or animal feed.

Catching chickens

Catching laying hens presents significant welfare challenges.^[25] Laying hens are quick and active animals during the day, making them difficult to capture in free-range housing systems like barns. This process can induce a lot of stress, leading to injuries as the hens may collide with each other and objects, which disqualifies them from being transported. To minimize stress, laying hens are typically caught in the dark while they are roosting and sleeping. Blue light is often used to keep the hens from waking up. However, some hens will inevitably wake and start moving, making them harder to catch and creating considerable unrest.^[26] Laying hens are caught by hand. Usually, specialized companies (poultry service companies) provide catching teams. Although these companies are often certified, they typically do not include animal welfare training. Consequently, the injury rate during catching is higher with these teams compared to "in-house" staff (poultry farmers, neighbors, etc.). Other contributing factors to this increased rate include time pressure, routine work, and a lack of awareness that live animals are being handled (desensitization).^[26] The low economic value of laying hens (currently less than 50 cents each) also means that they are not treated with the highest level of care.^[25] Chickens are often grabbed by their legs and held upside down, dangling from the catcher's hand. A catcher may continue until they have three or four chickens in one hand. When they grab the next chicken, the ones already being held often hit the floor or coop. By the time they are removed, the laying hens are completely exhausted, with few feathers and muscles, and brittle bones (osteoporosis) due to the high calcium demand during laying. As a result, they are prone to injuries during catching, especially to their legs and wings.^[25] The chickens are then literally crammed into plastic crates; often several at once, and this is done quickly and roughly to prevent those already inside from jumping out. Each crate holds 10-15 hens, each with less space than half an A4 sheet of paper. Hens weigh an average of 1.7-1.9 kg and are legally entitled to only 160 cm² per kg of chicken.^[27] The entire catching process takes an average of 2.8 hours.^[26]

Transport

The hens are packed tightly into crates and transported to the slaughterhouse. Due to having few feathers and minimal muscle tissue after laying, they are highly vulnerable to cold stress during transport. For instance, research by Wageningen University & Research (WUR) has demonstrated that in winter, laying hens were transported outside their comfort zone of 10-25°C for about a third of the time.^[26] The hens also faced significant temperature fluctuations; within just a few hours, the temperature could rise from around freezing (during transport) to 30°C (while waiting at the slaughterhouse). In the same investigation, the average transport time was an astonishing 10 hours (within the Netherlands). Of this duration, only a small fraction was spent driving (an average of 2 hours), while the trucks remained stationary for extended periods in the receiving area of the slaughterhouse (an average of 8 hours). Transport times can easily exceed 12 hours if slaughter occurs later in the day. Additionally, the hens have been fasting (without food) in the barn for a considerable time, leaving them without food and water for an extended period. On average, the hens studied went without food for a full 18 hours. There are only two slaughterhouses in the Netherlands that process laying hens. Consequently, a large number of these hens are shipped abroad, primarily to Poland, where they can be slaughtered at a lower cost. According to the Netherlands Food and Consumer Product Safety Authority (NVWA), 5.5 million laying hens were transported to Poland in 2015, accounting for approximately a quarter of the total number of hens slaughtered annually. Around 2.5 million laying hens were sent to countries such as Belgium, Germany, and France. In total, 14% of the chickens shipped went to slaughterhouses with a transport time exceeding four hours.^[28] Males from the laying hen chain (such as parent stock) are always sent abroad, as there is no slaughterhouse in the Netherlands that processes these males due to their size. Transport times for these males are often much longer than the previously mentioned times for transport within the Netherlands. There is no legal maximum transport time. However, hens transported for over 12 hours must be provided with food and water. In practice, this is nearly impossible because the crates are stacked on top of and beside each other, making the inner crates inaccessible. Furthermore, there is minimal monitoring of this, as it occurs abroad. Legally, a 2% injury rate and a 0.5% mortality rate are allowed for the capture and transport of spent hens. This theoretically results in 0.5 million injured hens and 130,000 dead hens arriving at the slaughterhouse each year. The Netherlands Food and Consumer Product Safety Authority (NVWA) conducts (limited) inspections for injuries sustained during capture and transport and has already issued 112 fines in the first half of 2017 for exceeding the legally established tolerance limits.^[29] However, inspections cease at the border.

Feather pecking

Chickens in modern livestock farming often show abnormal behavior due to stress, which likely comes from growing up without a mother.

For example, "gentle feather pecking" is a natural social behavior in chickens. However, this gentle pecking can escalate to more aggressive pecking, which may damage and pull out feathers. This results in bald patches, and the pecking can extend to the chicken's skin (known as cannibalistic pecking), leading to wounds. The sight of blood triggers even more intense pecking and can eventually lead to cannibalism. This represents the final stage of feather pecking and often results in death. Feather pecking often also includes pecking at combs, wattles, legs, and the cloaca (the gut, urine, and egg duct). Incidentally, this intensive feather pecking has nothing to do with the "pecking order," as pecking specifically targets the head or neck and rarely leads to feather loss.^[30]. This feather pecking does not occur in the wild, but wild chickens also show feather pecking when kept in captivity, indicating that the primary cause is stress.

Feather pecking is a tough and ongoing issue that leads to serious welfare concerns. This problem is especially challenging for farmers when chickens are free-range and their beaks are not trimmed. In free-range settings, farmers find it harder to keep an eye on feather pecking. Additionally, untrimmed beaks can inflict more damage than trimmed ones.

Feather pecking is influenced by several factors. The key factors include the mother's care of her chicks and the stress she experiences, the feeding and foraging behaviors of both young and adult animals, and the impact of stress and anxiety overall^[31]. Genetic factors also contribute. Unfortunately, much of the research aimed at preventing feather pecking primarily addresses the economic losses it causes, often neglecting the welfare of the hens.

As we have observed, chicks develop without their mothers. They hatch in an incubator and then grow alongside other chicks. Although chickens become independent shortly after hatching, their mothers guide them on what to peck, when to rest, and how to act. The lack of a mother in contemporary laying hen farming likely has a significant and often overlooked impact on how chicks and hens interact with each other and their capacity to exhibit normal or natural behaviors.^[32].

Litter and other distractions can help reduce feather pecking, but they aren't enough on their own. For instance, chickens from organic farms that have litter and free-range access to the outdoors still show signs of feather pecking.

Chickens tend to peck more aggressively at unfamiliar chickens compared to familiar ones. However, in larger flocks, pecking often decreases. This likely happens because there are so many unfamiliar chickens that it's impossible to chase away all the "competitors."

Each year, around 54 million chickens have their beaks shortened (burned) to prevent injuries from pecking^[33]. Since 2015, beak shortening has only been allowed using infrared radiation, which produces intense heat that causes beak tissue to die within a few weeks, resulting in the tip of the beak falling off. Starting in 2018, beak shortening will be banned by law.^[34]

Research has been ongoing regarding selective breeding to reduce aggression and provide more spacious environments to prevent beak pecking, especially in light of the ban on beak trimming.^[35] However, beak pecking continues to be the primary welfare issue for laying hens. A investigation conducted in 2006 across 29 different organic farms revealed that the situation was still concerning.^[36] Research from 2017 indicates that there is still much to learn about feather pecking, particularly regarding effective prevention methods.^[37] The question remains whether the ban on beak trimming is merely shifting one welfare issue while worsening another.

Failure and diseases

When farmers began raising laying hens on a large scale, the rate of premature deaths (failure) increased from 5-6% to as high as 20%.^[38] This rise was primarily due to the spread of diseases caused by overcrowding. Only through various artificial interventions, such as vaccination, could the mortality rate be lowered. The use of battery cages was also a response to this issue; it significantly reduced contact between hens and kept them separated from their droppings. However, with the abolition of battery cages, some of these problems are resurfacing. Research has shown that in housing systems where laying hens are no longer confined to cages, there is a higher incidence of (old) diseases, likely because chickens have more contact with each other and their droppings, which harbor many pathogens.^[39]

Generally, the mortality rate during the laying season shows a clear pattern. The initial period when a flock of laying hens is introduced to a barn is very stressful. For instance, chickens may crush one another, begin pecking at feathers, or suffer slow deaths due to an inability to find water and/or food in the new coop. Once the chickens adjust to their new environment, mortality between 30 to 50 weeks remains relatively stable and low (up to about 2%). However, after 50 weeks, the mortality rate rises again to around 8%, primarily because the hens are already "worn out," leading to decreased resistance.^[21]

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A distinction can be made between "natural" death and death caused by disease. Natural death is often associated with egg laying. A recent American study found that 26.6% of laying hens that died "naturally" succumbed to Egg Yolk Peritonitis (EYP).^[40] The oviduct is a funnel-shaped structure that collects the egg as it is released from the ovary. In laying hens, this process can frequently fail or even stop permanently, causing the egg to enter the abdominal cavity instead of the oviduct. Undeveloped eggs can accumulate there and become infected, ultimately leading to death.

Chickens can catch various diseases and parasites. This is partly because selective breeding for maximum egg production has weakened their immune systems, making them less resistant.^[41] Additionally, the chickens often experience stress, which further decreases their resistance.^[42] Furthermore, laying hen houses provide perfect conditions for disease spread due to the high density of birds, the consistently warm temperatures throughout the year, damp and dark areas, and contact with their own feces (manure).

Red mites or bird mites

The red mite has become well-known and infamous due to the fipronil scandal, which led to the culling of over 2.5 million healthy chickens. The term "red mite" is actually a misnomer; it refers to the poultry mite, which is a type of mite, not a louse. This is the most common parasite found in laying hens across Europe. In the Netherlands, 94% of poultry farms are infested with these mites, and a single chicken can harbor between 50,000 and 500,000 mites. The poultry mite is also capable of transmitting viruses and bacteria. The hens experience stress from the itching caused by the mites, leading them to peck at the mites and injure their own feathers. This itching and stress can also trigger increased aggressive behavior, which exacerbates feather pecking. Ultimately, the hens may die from blood loss and/or severe feather pecking.^[43] As a result, fewer eggs are produced, and the quality of the eggs decreases.

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The poultry mite flourishes in the highly unnatural conditions that laying hens endure.

E. coli

An infection with the bacterium Escherichia coli (E. coli) is a leading cause of mortality.^[21] This infection typically involves a specific type of E. coli known as APEC (Avian Pathogenic E. coli), and the disease it causes is called colibacillosis.

E. coli thrives at temperatures between 18-44°C, making the barn climate perfect for its growth, as it maintains a steady temperature of around 20°C.

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Bird flu

Avian influenza is likely the most recognized disease affecting chickens, mainly because it frequently makes headlines due to the numerous cullings. Bird influenza has two types: the mild variant, known as low pathogenic, and the dangerous variant, called highly pathogenic or avian flu. Animals infected with the mild variant usually show few symptoms. However, laying hens are still culled since this mild variant can evolve into the dangerous form. In rare instances, some types of bird influenza can also infect humans.

In 2003, avian influenza devastated the poultry industry, destroying one-third of all poultry farms. Thirty million birds were killed using electric shock or gassing. The H7N7 strain infected 89 people, and one of them did not survive.

In 2016, the industry culled over 1 million laying hens due to the H5N8 strain to stop its spread to other farms. That year also saw the longest indoor confinement of chickens in the Netherlands, lasting five months. Fortunately, this strain did not spread to humans.

In December 2017, avian influenza was detected on a meat farm, leading to the culling of 16,000 ducks. Since the virus was suspected to be a highly pathogenic H5 strain, authorities issued a nationwide order to confine birds indoors.

Free-range poultry are at a higher risk of contracting bird flu^[49]. Wild (migratory) birds, like ducks and geese, are often blamed for spreading the disease to laying hens. However, research from 2014 indicates the opposite; migratory birds do not introduce the virus into the country, but instead contract it here^[50].

Vaccination against bird flu is feasible; however, it is not primarily pursued for economic reasons. The process is challenging and costly, and our key export partner, Germany, does not accept products from vaccinated animals.^[52].

This disease thrives in chickens due to the unnatural conditions they are kept in. Low resistance, high chicken densities, and a barn climate that is damp, dark, and warm create the perfect environment for the virus.

Sternum abnormalities

A 2015 Flemish study found that after 60 weeks, 60% of laying hens in aviary houses exhibited a breastbone abnormality^[54]. Research conducted by the Institute for Agricultural and Fisheries Research (ILVO) in 47 Belgian aviary hen houses revealed that an alarming 82.5% of hens had experienced one or more fractures by the end of the production cycle. In comparison, this percentage was 58% for floor-fed hens and 62% for those in enriched cages.^[55]. The ILVO study also indicated that 59.8% of the hens examined had a curvature (deviation) of the breastbone^[56]. Deviations are primarily caused by the shape and material of perches; hard, inflexible materials lead to greater deformations of the sternum compared to softer, flexible materials^[53]. When a hen perches, two-thirds of her weight is supported by her breastbone.

Fractures and their repairs greatly affect the well-being of hens. Research indicates that hens with repaired fractures experience chronic pain.^[57]. Moreover, repaired fractures limit the hen's mobility and negatively influence egg production.^[58].

Osteoporosis

Bone loss, or osteoporosis, is a major cause of weak bones and fractures, often exacerbated by insufficient exercise. Laying a large number of eggs places significant demands on a hen's body. For instance, the calcium required for the eggs a hen lays during a laying period is 20-30 times more than what she can store.^[59]. As calcium is drawn from the bones to form the eggshell, the bones become more fragile. This increases the likelihood of fractures, particularly towards the end of the laying cycle, which can be very painful. In cages, where laying hens experience greater bone decalcification due to restricted movement, it is estimated that 80 to 89% of them suffer from osteoporosis^[60]. It has also been estimated that 13 to 35% of deaths in cages are attributed to osteoporosis. In free-range barns, although the overall mortality rate is higher, the proportion of deaths due to osteoporosis is lower.^[35].

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A recent American study revealed that among the laying hens that died 'naturally', up to 16.8% had succumbed to hypocalcemia^[40]. Hypocalcemia is a condition characterized by insufficient calcium in the blood, as most of the calcium is redirected to egg production. This deficiency can lead to muscle cramps, and the chickens may die from suffocation.

Foot problems

Foot and sole problems are common in poultry, including hyperkeratosis, footpad dermatitis, and bumblefoot. Key factors contributing to these issues include the type of barn, wet litter, perch and flooring materials, perching behavior, and poor leg hygiene.

Hyperkeratosis is a severe thickening of the skin on the feet due to excessive keratin production. Footpad dermatitis is an inflammation beneath the skin of the foot's sole, which can result in dead tissue and ulcers. In severe cases, this condition may progress to spherical lesions and swelling, known as "bumblefoot," which is extremely painful. Bumblefoot is especially prevalent in environments with hard perches. Poor hygiene, such as wet litter or manure, heightens the risk of developing bumblefoot syndrome.^[61]. This condition is more common in free-range barns with hard flooring and limited vegetation access.

A study conducted on 47 farms in Belgium found that an alarming 71% of laying hens suffered from foot problems over a 60-week period. The most prevalent issue was hyperkeratosis, affecting 42% of the hens.^[53].

Cloaca prolapse

When laying eggs, the final section of the oviduct turns inside out and temporarily extends outside the body, enabling a clean egg to be laid. However, sometimes the oviduct fails to retract properly and stays outside the cloaca. This issue is particularly prevalent in older animals, as the muscles responsible for retraction may have weakened due to frequent egg-laying sessions.^[62].

A noticeable chicken attracts the attention of other chickens, leading to a worsening situation.

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Different stable systems and animal welfare

There are several ways to keep chickens. The eggs laid by the hens are provided with codes, and the cartons often also carry a quality mark to indicate how the chickens were kept and which welfare criteria were met. The eggs themselves must always be stamped with numbers and letters. The first digit is the so-called egg code. This code consists of a number from 0 to 3 and provides information about the housing of the laying hens.

Cage systems

Although battery cages are banned, "enriched cages" are still allowed. In these cages, hens cannot spread their wings. Each hen has a minimum space of 750 cm², which is about 1.2 times the size of an A4 sheet of paper. This is slightly more space than in traditional battery cages, where hens had only 0.9 times an A4 sheet. Cages are considered "small" if they hold up to 15 hens and "large" if they hold between 15 and 60 hens. The space per hen remains the same in both small and large cages. These cages feature a mesh floor that lets manure fall through and be collected underneath.

Compared to traditional battery cages, enriched cages have some added features, or enrichments, such as a perch, a nesting box, and a litter area. Although enriched cages will eventually be banned, the deadline has already been pushed back from 2017 to 2021.

Another type of cage system is colony housing, where 30 to 60 chickens live in a large cage with at least 2.5 m² of space. In this setup, each chicken has a minimum area of 900 cm², which is about 1.4 times the size of an A4 sheet. This type is also known as a "small aviary" and includes the same enrichments as enriched cages.

Free-range systems

In a free-range coop, hens can move around freely, with feeding and drinking stations placed in various locations throughout the coop. The floor typically consists of a combination of slatted and solid surfaces (at least one-third of the total area), along with littered areas for scratching. Nests for laying eggs and perches are also available. All facilities in the barn can be arranged on a single level (floor housing) or spread across multiple accessible levels (aviary housing). Having multiple levels allows for housing more laying hens within the same barn space. Laying hens in free-range barns have at least 1111 cm² of open floor space, which is roughly equivalent to less than two A4 sheets of paper. Free-range hens do not have unrestricted access to the outdoors and typically spend their entire lives indoors without exposure to natural daylight.

Greater freedom for a hen generally has a positive impact on the welfare of the chicken. This freedom enables them to forage and explore more, which helps reduce stress. Increased exercise also contributes to stronger bones and muscles, leading to better overall health compared to caged laying hens, which have limited exercise. However, the downside is an elevated risk of fractures and other injuries due to collisions, falls, and similar incidents. For example, modern laying hens are significantly heavier than their ancestors, but their wing strength has not increased. Additionally, chickens are primarily ground birds and not adept flyers. This can result in uncontrolled landings, falls, and/or collisions when jumping or fluttering between floors. Consequently, these injuries are more prevalent in multi-story housing like aviaries than in single-story housing.^[55]

Free-range barn system

There are also barn systems that provide free-range access to the outdoors. Free-range systems are similar to barn systems but offer hens the option to go outside. Typically, the run is covered with a paved surface (see also "egg quality marks"). In the run, laying hens have 4 m² per hen and must have outdoor access for at least 8 hours each day, with some exceptions for extreme weather and mandatory confinement. Free-range barns can be categorized into conventional systems (known as "Freiland chickens") and organically raised laying hens. Free-range hens are seldom fully utilized, and not all chickens take advantage of the free-range area. Utilization is greatly influenced by the layout, shelter, and flock size. For instance, in large flocks (10,000 hens or more), only 3-15% of the hens use the free-range area.^[63] Tests with tall elephant grass demonstrated that chickens made much better use of the free-range space because they had more shelter, which encouraged them to venture further from the barn.^[64] For practical reasons (maintenance and clarity), free-range areas are minimally equipped.

Reverse side free range

Free-range chickens are more vulnerable to predators such as foxes, martens, hawks, and buzzards, with predation mortality estimated at around 4%.^[65] Chickens are natural forest dwellers that seek refuge in dense bushes and are primarily alerted to danger by the dominant rooster. In a run, dense shrubs are either sparse or completely absent, which is inadequate for the large number of hens that roam there. An investigation of organically raised chickens revealed that in 80% of the runs examined, the amount of shelter constituted less than 25% of the total area.^[66] Trees in free-range areas are also used by birds of prey as vantage points for attacking chickens. Most laying hen farms lack roosters. Even if roosters were present, their presence alone was insufficient to prevent chickens from being captured. While roosters did attempt to fend off birds of prey, they were often not positioned correctly, and there was typically only one rooster for every 30 hens. The welfare of the predators themselves is also compromised. Permits to shoot foxes near poultry farms are being issued more rapidly.^[67] Although it is relatively easy to make free-range chickens “fox-proof,” birds of prey are protected and much harder to deter, as they approach from above. Experiments have been conducted using electric shock decoys and bait sprayed with a narcotic substance (lithium chloride) to create negative associations between birds of prey and chickens. Only the latter method appeared to be somewhat effective, but it is challenging to implement in practice.^[68] The figure below illustrates the distribution of laying hens across various housing systems in the Netherlands for 2016.^[69]

Rondeel and Kipster

This section discusses two free-range systems in detail, both of which claim to provide the highest level of animal welfare and have garnered significant media attention.^[70] These systems are the stables of Rondeel and Kipster.^[71] The Rondeelstal is a circular barn designed based on research from the WUR, aiming to combine convenience for farmers, sustainability, and chicken welfare into a flexible barn layout.^[72] The barn is divided into 6 separate sections, housing either 3,000 (small units) or 6,000 (large units) chickens, with a maximum capacity of 30,000 laying hens. The units are shaped like pie wedges, alternating between night quarters and day quarters. The night and day quarters are connected by retractable walls. The night quarters and nesting area feature a multi-level aviary system. The day quarters (free-range area) have a transparent roof for natural light and artificial grass flooring, along with boxes for dust baths and other amenities. The outer edge of the barn serves as the free-range area, also referred to as the forest edge.^[73] This run is covered and fenced to keep birds of prey out.

This system has received 3 stars from the Beter Leven quality mark awarded by the Dutch Society for the Protection of Animals (Dierenbescherming), similar to organically raised hens. However, the hens have significantly less space to roam compared to free-range or organically raised hens. While exact figures are not available, it is estimated that each hen has approximately 0.05 m² of space, compared to 4 m² for free-range or organic hens. According to the 3-star criteria set by the Dutch Society for the Protection of Animals (Dierenbescherming), a minimum of 216 m² of free-range space is required for a flock of up to 6,000 hens, which translates to a minimum of 0.035 m² per hen.^[74] This is over 100 times smaller than the space provided in a free-range chicken run. Currently, there are three Rondeel barns in the Netherlands, along with two smaller versions (mini- and micro-barns located in Amsterdam and The Hague, respectively). Kipster, co-founded by the former director of Rondeel, closely resembles the Rondeel barn in design. Although not circular, it features night quarters with an aviary system and a central, light-filled courtyard (free-range area) covered with sand/litter and equipped with various amenities. The outdoor free-range area, also known as the forest edge, is relatively small and surrounded by windbreak mesh on all sides. The barn is designed for 24,000 laying hens, and there is currently only one barn in the Netherlands, which opened in 2017. Kipster stands out from other systems in one key aspect: male chicks are not killed immediately after hatching; instead, they are raised for 15-17 weeks before being processed into rooster burgers. However, these male chicks are currently moved to a rearing house with the lowest permitted living standards for chickens, meaning they do not receive "Beter Leven stars." According to Rondeel and Kipster, the use of free-range in conventional systems is very limited, suggesting that the free-range area could be much smaller. The Kipster website states: "By law, we need 10 hectares of land to label our eggs as free-range. According to scientific research and the Dutch Society for the Protection of Animals (Dierenbescherming), our chickens don’t require that much space at all." However, as previously mentioned, the minimal use of the outdoor range is due to the barn's layout, shelter, and the size of the hens, not because chickens need less space. After all, their natural habitat spans several tens of hectares. Furthermore, this overlooks the fundamental principles of the Rondeel stable design as outlined by the WUR:^[72] Free-range access is essential due to market demand. However, according to the Wageningen University & Research (WUR), free-range access presents several (economic) challenges, including: - A diminishing price gap between eggs from free-range chickens and "standard" eggs. - Health risks for both humans and animals. Chickens are more susceptible to diseases outdoors due to their own manure and potential exposure to wild birds overhead (avian flu). They can also ingest harmful substances like dioxin. - Current systems lack transparency for farmers, particularly with outdoor ranges, making it challenging to monitor individual chickens effectively and increasing the risk of failing to identify victims of feather pecking or sick animals in a timely manner. Lastly, the WUR notes that while "what the chicken wants" is considered, it has not been proven that chickens necessarily need to forage outside and explore their environment; this could also be achieved indoors. These factors influenced the design of a small, covered run, similar to those used in the Rondeel and Kipster barns. While chicken welfare was an important consideration, compromises were made regarding economic and health factors, meaning animal welfare was not the top priority. During the assessment of the first laying cycle in a Rondeel barn, mortality rates were found to be lower than in other systems (including organic), but breastbone abnormalities were just as prevalent as in other systems, averaging 1.73 on a scale from 0 (good) to 2 (poor). Other findings, such as feather pecking, were less definitive due to the presence of both hens with intact and trimmed beaks in the barn.^[75]

Organic better?

Organic laying hen farming appears more favorable in theory (more space, free range, no beak trimming), but the mortality rate is 10-15% higher than the previously mentioned 8%.^[76] This is partly due to a rise in infectious diseases. Laying hens are kept in less controlled environments (variations in climate indoors and outdoors, increased exposure to potential pathogens and parasites in the soil, manure, and air, etc.), and feather pecking often worsens because their beaks are not trimmed. Consequently, organic chicken farming does not inherently guarantee better animal welfare.^[77] Other studies also indicate that no housing system is perfect for the hen's well-being.^[78] Organic eggs may display the following quality marks on the carton: Beter Leven 3 stars, EKO quality mark, or the European organic quality mark. To be classified as organic, chickens must also be fed organic feed in addition to fulfilling the welfare requirements.

Beter Leven

In addition to the systems mentioned, there is a wide variety of quality marks in circulation, which are explained in more detail below and summarized in Table 1. Several eggs from different housing systems receive 3 Beter Leven stars from the Dutch Society for the Protection of Animals (Dierenbescherming). This includes all organic eggs, as well as the Rondeel egg, the Kipster egg, the Gijs egg, the Vrolijke-Kip egg, and the Natural Beter Leven egg. The last five are non-organic, free-range eggs that meet the modified welfare requirements for 3 stars. However, Rondeel and Kipster eggs are assigned code 2 because the free-range area per chicken does not meet the requirements for code 1 according to European regulations. For products containing eggs, 95% of the animal ingredients must comply with the Beter Leven quality mark to qualify for that designation. Additionally, there are eggs labeled as whole-wheat, corn, sunflower, omega-3/Columbus, and four-grain, which indicate the type of feed the chickens receive. However, these labels do not provide any information about the living conditions of the chickens. It is also worth noting that the color of eggs does not reflect the chicken's lifestyle, but rather the chicken itself (specifically, which hybrid it is). Generally, brown chickens (with red earlobes) lay brown eggs, while white chickens (with white earlobes) lay white eggs, although this rule is not always consistent. Brown eggs tend to be slightly more expensive than white eggs because brown laying hens are typically larger and require more food.

Figure 5 shows a schematic representation of how many eggs are “produced” per housing system.