Eggs are produced by laying hens. Laying hens are specialised breeds of chicken that have been selected for their high rates of egg production and are different to the breeds reared for meat (broilers) (Figure 1).
Figure 1. Layer and non-layer hen. In a layer hen, the hip bones are widely spaced, and the breastbone is tilted downward, providing more room for the development of eggs inside the abdomen. On the other hand, in a non-layer the breast will be bigger, while the hips will be more narrowly spaced © University of Reading
The top global egg producer is China, followed by the combined EU-member countries. In 2018 the EU countries held 397 million laying hens. In Europe, the top egg producing countries are Germany, Poland, UK, France and Spain each contributing with approximately 11% of the total laying hens .
Production cycle of laying hens
The basic production cycle of laying hens is shown in Table 1 and the egg production cycle occurs as a natural process during the maturity stage. As the laying hens reach later stages of maturity, their egg laying rate gradually declines.
|Hatchery||Growing (18 weeks):||Maturity (19 to 60-70 weeks of age)|
|Chicks hatch in a specialised hatchery facility.||Pullets (young hens) are reared at a growing facility for 18 weeks.||Once they reach target body weight, hens are moved to a lay house and exposed to an increasing day length with artificial light to stimulate egg laying.|
|An egg takes 23-27 hours to form and be laid. The shorter the time, the more days in a row an egg will be laid.|
|Peak laying period 25-39 weeks of age. Egg laying then declines until the end of the lay. At approximately 72 weeks old, the birds leave the laying system.|
Figure 2: Life cycle of an egg laying hen, hatchery to maturity
Light is an important factor in stimulating hens to lay eggs. It is the main environmental cue that the hen receives, which in turn regulates hormone levels that affect egg laying . Both the duration of the light period and the intensity of the light are important, and farmers provide artificial lighting in specially developed cycles to optimise both frequency of production and the quality of eggs .
How eggs are produced
There are three different production systems in common use: cages, barns and free-range. The distribution by production system in the EU as of 2018 is shown in the pie chart below (Figure 3).
Figure 3: Methods of production communicated according to Commission Implementing Regulation (EU) 2017/1185 Source
The conventional, unenriched cage (‘battery cage’) was developed in the 1950s for high intensity egg production by maximising egg production per unit area .
Figure 4: Hens in battery cages in Bastos, São Paulo, Brazil. © Secretaria de Agricultura e Abastecimento do Estado de São Paulo Agriculturasp Source CC BY 2.0
Figure 5: Hardy Meyers chicken operation near Petal, Mississippi Source
The reduced welfare state of hens kept in conventional battery cages led to the EU banning their use in 2012, and the introduction of new minimum welfare standards for caged hens   . A new ‘enriched cage’ is now used in many EU countries, along with the other two common egg production systems. All the egg production systems in the EU are tightly regulated with respect to welfare standards .
In enriched cage systems, hens spend their productive life indoors in large cages with other hens, where they have access to all the facilities required to meet their essential needs . In barn-based systems hens are kept in large flocks in specialised barns, also designed to meet essential needs. In free-range systems, hens live in barns and are provided with access to an outdoor area during the day. Organic systems are similar to free-range but additional organic husbandry standards are met, including providing organically produced feed .
A comparison of the main features of the enriched cage and free-range systems is shown below:
|Enriched cage system||Free-range system|
|Setting||Indoors||Indoors with access to outdoors during the day|
|Egg mass||Average 57g||Average 60g|
|Stocking density (hens per unit area)||750cm2 cage area per hen.||At least 4m2 of range per hen.|
|Furnishing||Nests, perching space, bedding litter to peck and scratch, unrestricted access to feed and water troughs.||Nests, perching space, bedding litter to peck and scratch, unrestricted access to feed and water troughs. Outdoor ‘range’ area.|
|Feed||Specially formulated pelleted feed provided continuously.||Specially formulated pelleted feed provided continuously.|
|Feed conversion efficiency (g feed consumed/ g egg produced)||2.11||2.17|
|Production efficiency||Shorter production cycle in a controlled environment for mass production.||Longer production cycle with higher risks and operating costs.|
The biggest challenge the egg industry has faced is the transition from battery cages to enriched cages or free-range systems in order to improve animal welfare  . Consumer demand for non-cage produced eggs continues to rise across Europe . There are significant costs associated with transitioning from cage-based to free-range systems and at the same time, the farmer has to accept reduced feed efficiency and increases in rejected eggs. Meeting the hens’ nutritional requirements is a critical factor in production efficiency. Hens are monogastric and, like pigs, require a high energy and protein feed to maintain health and support egg production. Feed is typically given ‘ad libitum’, meaning hens can feed at any time and consume as much as they need .
References can be found under the ‘Downloads’ heading at the bottom of this Step. The figure for the stocking density of free range hens was updated (8.11.19) with reference to The Welfare of Laying Hens, RSPCA, August 2018.
What do you look for when buying eggs? Is the welfare of the chickens important to your decision making when purchasing? Does the packaging give enough information about how the chickens producing the eggs are kept?
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