Abstract:

Objective To comply with the trend of independent innovation in China's layer breeding industry and the upgrading of pink-shell egg consumption, address the specific breeding needs of Jiangsu Province, and solve the problems of insufficient laying performance, high feed-to-egg ratio, poor uniformity, and low profitability of culled hens in existing specialty layer breeds, a three-line crossbreeding system of small-sized, green-footed, black-feathered pink-shell layers was developed. By utilizing a three-line mating pattern combining local chicken resources with high-yielding layers, this work aims to integrate high laying performance with specialty traits, enhance the competitiveness of Chinese layer breeds, meet the market demand for high-quality specialty eggs and high-value culled hens, and promote industrial efficiency and farmers' income. Method During the development of the "Nongda No.6" layer crossbreeding system, the terminal sire (line H) was bred based on the black-feathered green-footed local chicken of Dongtai, Jiangsu Province (derived from crossing the black-feathered Yuanbao chicken with the Guifei chicken). The slow-feathering line A (a maternal line of the "Nongda No.5" small-sized layer crossbreeding system) and the fast-feathering line K (a paternal line of the "Nongjin No.1" layer crossbreeding system), both of the Rhode Island Red standard breed, were introduced as the first sire and the maternal line, respectively. The breeding methods comprehensively integrated individual phenotypic selection, testcross selection (e.g., for black feather/green foot traits in line H and homozygosity for slow-feathering in line A), molecular marker-assisted selection (using the MC1R gene to screen for the black feather trait in line H), index selection (for egg number), and sib selection (for sex-limited traits in males). Through a multi-stage selection procedure from day-old chicks to 66 weeks of age (including avian leukosis and pullorum disease purification, semen quality testing, and egg quality measurement), key indicators such as feather color, shank color, body weight uniformity, age at first egg, egg number at 43 and 66 weeks, egg weight, eggshell strength, eggshell glossiness and color, Haugh unit, yolk ratio, fertilization and hatchability rates, as well as avian leukosis/pullorum positive rates were systematically measured for each line. The superior performance of the commercial generation, including pink-shell egg production, strong disease resistance, persistent laying peak, as well as the product advantages of high eggshell strength, moderate egg weight, shiny pink eggs, and high-quality black-feathered, green-footed, small-sized culled hens, was validated through pilot tests. Result The breeding results showed that the parental roosters of the "Nongda No.6" crossbreeding system are black-feathered, green-footed and fast-feathering, while the parental hens are dark red-feathered, yellow-footed and slow-feathering. After five generations of selection, the rates of black feather, green foot and fast-feathering in the terminal sire line H all reached 100%. The commercial generation chickens are black-feathered, green-footed and fast-feathering, and lay shiny pink-shell eggs. The egg number at 43 weeks was increased by 12.8 eggs in line H. The slow-feathering rate in the first sire line A reached 100%, and the egg number at 43 weeks was increased by 7.5 eggs. In the maternal line K, the egg weight at 43 weeks was reduced by 2.1 g, and the uniformity of eggshell color was improved. Through continuous disease purification, the positive rate of avian leukosis in line H decreased from 0.36% to 0.01%, while lines A and K, as well as all three lines for pullorum disease, became completely negative. In terms of production performance, the survival rate of commercial generation chickens from 0 to 18 weeks was over 98%, the number of eggs per hen housed at 72 weeks reached 282.7–284.7, the average egg weight was 50.3 g, the feed-to-egg ratio during the laying period was as low as 2.28∶1, and the eggshell strength at 43 weeks reached 4.08–4.51 kg/cm², demonstrating comprehensive advantages including high egg production, low feed consumption, excellent egg quality and high residual value of culled hens. Conclusion The "Nongda No.6" layer crossbreeding system has successfully developed a specialty layer crossbreeding system characterized by high yield, superior quality and low input by integrating the black-feathered green-footed local chicken with the Rhode Island Red standard breed through systematic combining ability tests, pure line selection, molecular marker-assisted selection and disease purification. The Nongda No.6" not only aligns with the trends of the specialty consumer market but also meets the "two highs and one low" requirements of specialty layer farmers, i.e., low rearing cost for small to medium-sized hens, high egg price and high culled hen price. Therefore, it has broad prospects for promotion and application

Key words: "Nongda No.6" layer, Crossbreeding system, Breeding technology