1. Why Are Egg-Laying Chickens (Layers) and Meat Chickens (Broilers) Raised Separately?
Chickens raised for eggs are called layers, while those raised for meat are called broilers [1]. The distinction is not just about breed names, but about what humans have sought from the birds. The National Agriculture and Food Research Organization (NARO) explains that layers are breeds developed over many years to produce large numbers of eggs, while broilers are breeds selected to gain weight quickly and become larger [1]. Because the direction of selection differs, body shapes vary: layers tend to be slim, whereas broilers are large. Let us look at these results through numbers, starting with egg-laying chickens.
2. How Many Eggs Does a Laying Hen Produce in a Year?
A children’s page from the Ministry of Agriculture, Forestry and Fisheries states that one chicken produces an average of about 300 eggs per year and begins laying about 150 days after hatching [3]. NARO estimates around 280 eggs per year depending on the breed [1]. Since sources vary, it is safe to remember the range as roughly 280 to 300 eggs. A special feature from the Ministry notes that laying hens start producing about 5 months after hatching and reach peak production at about 7 months [2]. They lay about one egg per day, though there are days they do not, resulting in about 300 eggs a year [2]. Calculated over 365 days, 300 eggs equals about 0.8 per day. This means they lay almost every day. It suggests their energy is directed toward egg production rather than growing their bodies.
3. How Long Does a Meat Chicken Take to Grow to Shipping Size?
Broilers typically grow large and are shipped out in about 50 days [4]. Most of these are foreign breeds that grow quickly and have excellent feed efficiency [4]. Materials from Chiba Prefecture state they are shipped out in about 55 to 60 days after hatching, with variations by year and brand [5]. Here we read this as roughly 50 to 60 days. Compared to the roughly 150 days it takes for an egg-laying chicken to start laying, broilers are shipped out in about 50 to 60 days. By the time a layer produces its first egg, broilers could have been raised more than twice. In the Polish comparison study, at 6 weeks of age, the weight of male egg-type chickens was less than one-quarter that of broilers [6]. This rapid growth is the specialty of chickens selected for meat. Another study compared lineages from 1957 and commercial lines from 2005 raised on modern feed until 56 days, reporting that growth had increased by more than four times [7]. This shows the traces of selection work that has continued for decades.
4. What Does Selective Breeding of Chickens Involve?
"Selecting" means crossing chickens with desired traits and keeping only those offspring with the desired traits among the hatched chicks, repeating this over many generations [1]. The phrase "over many years" in NARO’s explanation refers to this long duration. According to the Japanese Wikipedia entry for broilers, they are derived from improved White Cornish breeds and others, and unlike laying hens, male chicks are also raised [8]. In the past in Japan, chickens that stopped laying eggs or males were used for meat, but specialized broilers were later introduced [8]. There is also a difference in rearing: unlike laying hens, male broiler chicks are raised as well [8]. These purpose-specialized chickens support current egg and meat production.
5. Where Do the Chickens Raised in Japan for Eggs and Meat Come From?
A special feature from the Ministry of Agriculture, Forestry and Fisheries states that most laying hens currently raised in Japan are born from parent chickens bred overseas [2]. White eggs are associated with breeds like White Leghorn, while brown-shelled eggs involve Rhode Island Red; Boris Brown is the most commonly kept breed for brown eggs in Japan [2]. Domestic Japanese breeds include Momiji and Sakura [2]. Most meat broilers are also described as foreign breeds [4]. There are different rearing methods for chicken meat. Chiba Prefecture materials state that "Jidori" (local chickens) have at least 50% blood from native breeds and are raised for more than 80 days after hatching [5]. Compared to the 50 to 60 days for broilers, this is a much longer rearing period. This is not about which is better; it depends on what was sought and how long the birds are raised. Let us look for these differences in our own egg packs and meat labels.
6. What Can Egg Packs and Meat Labels at Home Tell Us About Chicken Breeds?
Look at the egg pack at home. If it says "Aka-tama" (brown shell) or "Shiro-tama" (white shell), you can recall the connection to breeds like White Leghorn or Rhode Island Red [2]. Count how many eggs your family eats in a week. If one chicken lays 300 eggs a year, that is about 5.8 eggs per week (300 divided by 52) [3]. Converted to chickens laying 300 eggs a year, 12 eggs equal about two chickens' worth for one week (rough estimate). If the meat pack says "Jidori," it means the bird has at least 50% blood from native breeds and was raised for over 80 days [5]. If it does not say so, look for other labels. If you want to read the original sources, start with NARO’s Okazaki Farm "Q&A about Chickens," where differences between layers and broilers are explained in Q&A format [1].