Chicken is the world's largest meat production and consumption product, and about 70% of the world's chicken comes from white-feathered broilers. Chicken is my country's second largest meat product, and my country's chicken mainly comes from white-feathered broilers and yellow-feathered broilers. White-feathered broilers contribute about 45% to my country's chicken production, and yellow-feathered broilers contribute about 38%.

Figure 1 World Meat Structure (%, FAO)

Figure 2 China Meat Structure (%, FAO)

White-feathered broilers are the breed with the lowest feed-to-meat ratio, the highest degree of scale breeding, and the highest degree of external dependence among all livestock and poultry breeds in my country. All yellow-feathered broiler breeds used in my country's production are self-bred breeds, with the largest number of bred breeds among all livestock and poultry breeds, and are a successful example of transforming local breed resource advantages into product advantages.

1. Historical context of chicken breed development

The domestic chicken was domesticated from Asian jungle pheasants 7,000-10,000 years ago, and its domestication history can be traced back to more than 1,000 years BC. Domestic chickens are similar to jungle fowl in terms of body shape, feather color, and call. Cytogenetics and morphological studies have proved that jungle fowl is the direct ancestor of modern domestic chickens. The genus Gallus is divided into four species, namely red jungle fowl (Gallus gallus, Figure 3), green-collared jungle fowl (Gallus various), black-tailed jungle fowl (Gallus lafayetii) and gray-striped jungle fowl (Gallus sonnerati). There are two different views on the origin of domestic chickens from jungle fowl: the single origin theory believes that red jungle fowl may have been domesticated once or more times; the multiple origin theory believes that in addition to red jungle fowl, other jungle fowl are also the ancestors of domestic chickens. At present, most studies support the single origin theory, that is, domestic chickens mainly originated from red jungle fowl.

Figure 3 Red Junglefowl (Dorian Anderson, 05 Jan 2020, Phetchaburi, Thailand. eBird Checklist S63030704. Macaulay Library ML212770971)

　　(I) The breeding history of broiler chickens abroad

Before the 1930s, group selection and pure line breeding without pedigree records were carried out. The main selection trait was egg-laying performance, and chicken was a by-product. At that time, chicken breeding belonged to the small-scale courtyard economic model. With the invention of the closed egg-laying box in the 1930s, egg-laying performance began to be selected according to individual egg-laying records; from the 1930s to the 1950s, hybrid advantages were introduced into chicken breeding by drawing on the corn double hybrid technology, which quickly replaced pure line breeding and became the mainstream of commercial chicken production. The hybrid matching method has gradually developed from the earliest binary hybrid to the three-way and four-way hybrid matching. After the use of pedigree records in the 1940s, the selection efficiency of limited traits and low heritability traits was improved, and inbreeding depression caused by close relatives could be effectively avoided. After 1945, some third-party institutions or test stations in Europe and the United States carried out random sample tests of chicken production performance, with the aim of objectively evaluating the participating varieties under the same environmental conditions, which played a positive role in increasing the market share of varieties with excellent test performance. This type of performance measurement work was terminated after the 1970s. From the 1960s to the 1980s, the main traits that were easy to measure were selected, such as egg production, hatchability, growth rate and feed conversion rate, and the products were mainly bone-in chicken and household consumption. The single-cage measurement of feed conversion rate, which began in the 1980s, played a direct role in reducing broiler feed consumption and improving feed utilization. Since the 1990s, processing traits have received attention, such as eviscerated weight and boneless breast weight. The application of genetic evaluation methods such as the best linear unbiased prediction method (BLUP) and the advancement of computer technology have played an important role in breeding development. After entering the 21st century, broiler breeding began to consider product quality and animal welfare. At present, broiler molecular breeding technology represented by genomic selection (GS) at home and abroad is shifting from research and development to application.

　　(II) The history of broiler breeding in my country

In the mid-19th century, local chickens in my country were at the world's leading level in terms of egg-laying and meat-producing performance. For example, the United Kingdom introduced Langshan chickens and Jiujin yellow chickens from Jiangsu and Shanghai in my country, and then introduced them from the United Kingdom to the United States. After breeding, they were recognized as standard breeds in both countries. Langshan chickens are recognized as dual-purpose breeds, and Jiujin yellow chickens are recognized as meat breeds. These breeds have had an important impact on the formation of some world-famous livestock and poultry breeds. For example, the British Orpington and the Australian Black in Australia have introduced the bloodline of Langshan chickens in my country, and the Rock Chicken, Rock Island Red and other breeds also use Jiujin yellow chickens in my country as breeding materials. From the late 19th century to the 1930s, eggs and chicken in my country were important export products. However, for a long time thereafter, my country's poultry industry remained at the extensive breeding level, and the production level of chickens widened the gap with the world's advanced level. In the mid-1960s, Hong Kong selected Huiyang chicken, Qingyuan Ma chicken and Shiqi chicken from three local breeds in Guangdong as the main improvement objects, and successively introduced the new Hanxia, White Rock, White Cornish and Hubbard breeds for hybridization, and bred the Shiqi hybrid chicken, which played an important role in the production and consumption of broilers in Hong Kong. In the 1970s and 1980s, the Shiqi hybrid chicken was introduced to Guangdong, Guangxi and other places, and hybridized with recessive white chickens to form the improved Shiqi hybrid chicken and promote it in large quantities in production. From the 1960s to the 1980s, my country used hybrid breeding and family selection methods to breed broiler breeds such as the New Langshan Chicken, the New Pudong Chicken and the New Yangzhou Chicken. From 1983 to 2015, the yellow-feathered broiler chicken adopted the northern breeding and southern breeding model, making full use of the differences in climate, ecological environment, feed, manpower and breeding technology between the north and the south. The parent-generation breeder chickens were raised in northern regions such as Henan, Shanxi and Shaanxi, and the commercial-generation breeder eggs were transported back to the south for hatching and breeding, which improved the production efficiency of yellow-feathered broilers. The systematic breeding of yellow-feathered broilers began in the late 1980s. The introduction of recessive favorable genes such as the grain-saving dwarf gene (dw gene) and the recessive white feather gene played an important role in the breeding of yellow-feathered broilers in my country. About one-third of the yellow-feathered broiler breeds in the country have applied these technologies. In 1986, Guangzhou Baiyun Poultry Development Company introduced recessive white and other varieties and hybridized them with Shiqi hybrid chickens to breed 882 yellow-feathered broilers. In 1999, Shenzhen Kangdal (Group) Co., Ltd. bred Kangdal Yellow Chicken 128, the first yellow-feathered broiler matching system approved by the state (Figure 4). After that, the breeding of new yellow-feathered broiler varieties in my country entered a rapid development period. In order to cooperate with the variety approval work, the Poultry Quality Supervision, Inspection and Testing Center (Yangzhou) of the Ministry of Agriculture and Rural Affairs and the Poultry Quality Supervision, Inspection and Testing Center (Beijing) of the Ministry of Agriculture and Rural Affairs were established in 1998 and 2003 respectively, responsible for the national poultry production performance measurement work.

　　Figure 4 Kangdal Yellow Chicken 128 Supporting System (Nong09 New Variety Certificate No. 1, 1999)

In the mid-1980s, Beijing Poultry Breeding Company, a joint venture between China, the United States and Thailand, introduced the pure Avian line from the United States, which started the local breeding of white-feathered broilers in my country. By 2001, domestic Avian broilers accounted for more than 54% of the domestic market. Later, due to problems such as disease prevention and control, local breeding fell into a trough in 2004. In 1988, approved by the State Planning Commission, the National Poultry Breeding Center of the Ministry of Agriculture was established in Wuqing, Tianjin, planning to independently cultivate white-feathered broiler varieties by introducing foreign pure lines or synthetic lines. The center covers an area of 2,000 acres and has 44 chicken houses, including resource farms, breeding farms and great-grandparent farms. The design scale is to raise 88,600 breeders and provide 4.28 million grandparent eggs annually. However, the center has not been operating normally and was transformed after July 2008. In 2009, the National Broiler Industry Technology System established a white-feathered broiler breeding collaboration group to conduct strategic research on white-feathered broiler breeding in my country and organize and promote capable enterprises in my country to carry out white-feathered broiler breeding. In 2014, the National Broiler Genetic Improvement Plan (2014-2025) was issued and implemented, which clearly included white-feathered broiler breeding in the development goals, which has promoted the breeding of white-feathered broilers in my country. In 2019, the Ministry of Agriculture and Rural Affairs implemented a joint research project on white-feathered broiler breeding and began to promote white-feathered broiler breeding.

　　II. Development of modern broiler breeding at home and abroad

(I) Development abroad

Genetic breeding progress since the late 1950s has laid the foundation for modern chicken production, promoted the development of egg and chicken production towards specialization, and broiler production has become an independent poultry industry. Over the past 80 years, North American and Western European countries have carried out systematic genetic breeding on the growth rate, feed conversion and carcass composition of chickens, forming today's white-feathered broiler breeds and quickly occupying the global market. The father line of modern white-feathered broilers comes from White Cornish and the mother line comes from White Plymouth Rock, which produces hybrid advantages through system matching. At present, including my country, the varieties used in the production of commercial white-feathered broilers in the world mainly include a few varieties such as AA+, ROSS, COBB, HUBBARD, etc., which come from Aviagen and Cobb-Vantress respectively. White-feathered broilers have a mature and complete breeding system, forming a pyramid structure consisting of breeding core groups, great-grandparents, grandparents, parents and commercial chickens. The genetic progress of the core group needs 4-5 years to be transmitted to commercial chickens (Figure 5). After expansion, one core group hen can produce more than 3 million commercial broilers and more than 5,000 tons of chicken meat. At present, the world produces about 11.6 million sets of white-feathered broiler grandparent breeders, about 600 million sets of parent breeders, and about 80 billion commercial chicks each year.

Figure 5 Broiler breeding system

In order to meet the market demand for chicken quality and animal welfare, some European countries have also launched a small number of slow-growing and colored-feather broiler products similar to my country's yellow-feathered broilers. Hubbard JA, Rowan Ranger, Sasso Label Rouge, etc., which are now owned by Aviagen, are all slow-growing chicken varieties. In addition, European countries also produce different types of slow-growing broilers through simple hybridization of fast-growing chickens and slow-growing chickens. Label Rouge chickens are bred for meat quality, and their production accounts for about 15% of the total chicken production in France. Together with other types of slow-breeding chickens, slow-breeding chickens account for 24% of the total chicken production in France. The Dutch slow-breeding chickens are developing rapidly, mainly considering meat quality and animal welfare, and their production has reached more than 40% of the total chicken production.

　　(II) Domestic Development

1. Yellow-feathered broiler

Yellow-feathered broiler, also known as three-yellow chicken and high-quality chicken, originally refers to chickens with yellow feathers, yellow skin, yellow legs, slow growth rate, and excellent meat flavor. Now it generally refers to the local breed chickens listed in the "Chinese Livestock and Poultry Genetic Resources·Poultry" and the "Livestock and Poultry Varieties" of various provinces, cities, and autonomous regions, as well as broiler breeding lines and varieties (matching lines) containing the blood of these local breed chickens, including broiler chickens with yellow feathers, hemp feathers, black feathers, etc. At present, all the yellow-feathered broiler varieties used in my country's production are self-bred varieties, and the number of broiler varieties is the largest among all livestock and poultry varieties. It is a successful example of transforming the advantages of local variety resources into product advantages. By 2020, 59 yellow-feathered broiler varieties will be approved by the state, which can be further divided into three categories according to growth rate and market age: fast-growing, medium-speed and slow-growing, to meet diversified market needs. In recent years, with the increasingly stringent requirements for epidemic prevention, various places have formulated "live ban" policies. In addition, the new business model of "Internet + express delivery" has promoted the consumption of slaughter products. In the future, the slaughter and listing of yellow-feathered broiler chickens will become a general trend, and the corresponding variety breeding will also develop towards slaughter-type varieties. After selection and verification by the Ministry of Agriculture and Rural Affairs, there will be 17 national broiler core breeding farms and 16 bases for the expansion and promotion of improved varieties in the country in 2020.

2. White-feathered broiler chickens

Before the outbreak of avian influenza in the United States in 2014, more than 95% of my country's imports of white-feathered broiler grandparent breeders came from the United States. Since then, with the development of avian influenza epidemics around the world and the adjustment of my country's customs import policies, my country has successively introduced white-feathered broiler grandparent breeders from the United Kingdom, France, Spain, Poland, New Zealand and other countries. my country imports 800,000 to 1.2 million sets of grandparent breeders annually, with an annual introduction amount of about US$40 million. In 2019, there were 1.39 million sets of grandparent white-feathered broilers in stock nationwide, 51.43 million sets of parent stock, 4.7 billion commercial chicks were produced, and the output value of white-feathered broilers was about 150 billion yuan per year. my country's large white-feathered broiler breeding companies include Shandong Yisheng Breeding Livestock and Poultry Co., Ltd., Fujian Shengnong Development Co., Ltd., Shandong Minhe Animal Husbandry Co., Ltd., etc.

3. Small white-feathered broilers

There is another type of breed in my country's broiler production - small white-feathered broilers. Typical small white-feathered broilers are broilers produced by hybridization with white-feathered broiler paternal roosters as the father and high-yielding brown-shelled laying hens as the mother. The commercial generation has white feathers all over the body, occasionally with black or red spots, yellow beaks, shanks, toes, and white skin. The cost of small white-feathered broiler commercial chicks is low, and the growth rate and meat quality are between fast-growing large yellow-feathered broilers and white-feathered broilers, which are suitable for processing traditional chicken products such as braised chicken. A prominent problem in the production of small white-feathered broiler chickens is the non-standard seed production. In 2018, the broiler WOD168 complementary system was approved by the National Committee of Animal Genetic Resources, marking the first step towards standardization of small white-feathered broiler seed production.

　　3. Problems and gaps

(I) Breeding of white-feathered broiler chickens

Compared with the advanced level of international white-feathered broiler breeding, my country's independent white-feathered broiler breeding time is short, the accumulation of high-performance genetic materials is weak, the application of new technologies such as molecular breeding is insufficient, and there is a large gap in the research and development of seed-borne disease purification technology and detection products. The details are as follows:

1. Breeding materials. Multinational companies have a series of excellent strains with fast growth and high meat production rate, and through the merger and reorganization of broiler and laying hen breeding companies, the materials and genes are further enriched, providing a guarantee for the breeding of new varieties; my country's white-feathered broiler breeding resources have a weak foundation for cultivation, and the number of excellent breeding materials is small.

2. Breeding technology. Compared with international multinational companies with hundreds of years of breeding experience, my country's white-feathered broiler breeding started late, and the research and application of balanced breeding technology between growth and reproduction traits is far behind the international advanced level. The application of new technologies such as genomic breeding is not high; there is a lack of high-throughput phenotypic intelligent precision measurement technology, and the application of automatic data collection and transmission is low.

3. Seed disease purification technology. International large-scale poultry breeding companies have taken effective purification measures for vertical transmission of seed diseases such as avian leukosis and pullorum, which has significantly improved the competitiveness of products. The purification of avian leukosis and pullorum is a shortcoming that hinders the development of my country's breeding poultry industry, and the detection kits are heavily dependent on imports.

(II) Yellow-feathered broiler breeding

my country's yellow-feathered broiler breeding and production are at the world's leading level. However, there are many breeding companies with uneven scales, weak overall technical strength, insufficient application of advanced breeding technology, and relatively backward breeding facilities and equipment; there is a certain degree of repeated breeding phenomenon, and there are few core varieties with obvious characteristics, excellent performance and large market share; for a long time, the breeding goal has been to adapt to the sale of live poultry, such as feather color, body shape and appearance, which are related to breeding. It is impossible to meet the market demand for centralized slaughter and fresh-market products under the new situation.

my country is rich in local chicken breed resources, and many excellent genetic characteristics have been formed under long-term and complex ecological and socio-economic conditions. However, for a long time, there has been a lack of in-depth research on the characteristics of germplasm resources, insufficient investigation of variety resources and evaluation of variety characteristics, and insufficient information support for analysis and evaluation. In addition, the construction of a dynamic monitoring system for variety resources is insufficient, and the evaluation of the characteristics of genetic resources with strong adaptability, high yield and high quality is not comprehensive and systematic, resulting in a serious lack of exploration and utilization of the excellent characteristics of local varieties, hindering the protection and development and utilization of local genetic resources, and affecting the production level of China's poultry industry, the market competitiveness of poultry products and the sustainable development of the poultry industry.

　　IV. Development direction of the 14th Five-Year Plan

(i) Accelerate the cultivation of domestic white-feathered broiler seed sources

We should adhere to the principle of combining introduction and breeding with self-reliance. Maintaining appropriate imports and combining introduction and breeding will be conducive to the healthy development of my country's white-feathered broiler seed industry. However, in terms of variety access, domestic and foreign varieties should be treated equally.

(ii) Improve the carcass quality and standardized scale breeding level of yellow-feathered broiler chickens

With the in-depth promotion of the "live ban" policy across the country, the slaughter and listing of yellow-feathered broilers has become an irreversible development trend. Yellow-feathered broiler breeding should pay more attention to the appearance and quality of the carcass. Compared with white-feathered broilers, yellow-feathered broilers overemphasize regional demand characteristics, and have prominent problems such as multiple varieties and types, low market share and small enterprise scale. We should continue to promote standardized scale breeding, increase the market share of core varieties, and make seed companies bigger and stronger.

(III) Strengthen the research and development and application of precision breeding technologies such as intelligent and phenotypic groups

At present, the determination of broiler traits in my country is still mainly based on manual observation and manual measurement. In view of the precise requirements of phenotypic data volume and accuracy for broiler breeding, it is necessary to vigorously promote the development and application of intelligent non-destructive determination technology and equipment in broiler core breeding farms under the condition of significant improvement of 5G transmission and big data analysis capabilities, and improve the ability to accurately obtain phenotypic big data such as meat production, lipid reduction, feed conversion, and egg production performance; based on multi-omics methods such as genome, transcriptome, and metabolome, combined with gene editing technology, systematically analyze the genetic mechanisms of muscle growth and development, fat deposition, sex differentiation and development, body nutrition metabolism, and appearance trait formation, and dig out functional genes or molecular elements that affect important economic traits of broilers, providing a strong basic guarantee for the application of molecular technology to accelerate broiler breed improvement. Accelerate the application of whole genome selection technology in broiler breeding.

(IV) Strengthen the exploration and innovative use of chicken germplasm resources

It is of great significance to comprehensively and systematically evaluate the genetic characteristics of local chicken breeds in my country, explore excellent genetic resources such as reproduction, feed conversion efficiency, meat quality, and resistance, and use modern biotechnology methods to cultivate new excellent chicken strains and genetic materials that meet the needs of market and industrial development with local chicken breeds with excellent meat quality, flavor characteristics, and resistance as materials, turning resource advantages into market advantages, promoting the protection, development, and utilization of my country's chicken genetic resources, and promoting the independent development of my country's chicken breed industry.