Animal Molecular Breeding, 2025, Vol.15, No.2, 60-71 http://animalscipublisher.com/index.php/amb 61 Based on the above background, this study will review important research progress in the field of epigenetic regulation in recent years based on the two themes of duck growth and feather development. We will explore the role of epigenetic mechanisms in the growth process of ducks (including muscle and skeletal development, metabolic regulation, etc.) in the embryonic and growth fattening stages; focus on explaining the epigenetic regulation of duck feather development (hair follicle generation, feather differentiation and replacement); aim to systematically summarize the current research status of epigenetic regulation of duck growth and feather development, and provide a scientific basis for the future application of epigenetic principles in poultry production. 2 Overview of Duck Growth and Feather Development 2.1 Characteristics of growth and development stages Ducks grow and develop through multiple stages in the embryonic and postnatal periods. Duck embryos can hatch out of the shell after developing in fertilized eggs for about 28 days. The embryo development speed and tissue differentiation of the fertilized eggs are affected together with the nutrition of the fertilized eggs and the external hatching environment. After being released from the shell, the meat duck can reach the market weight at about 58 weeks of age. This rapid growth is due to breeding improvement and efficient feeding, but is also closely related to endocrine regulation and epigenetic mechanisms. During the growth of ducks, the number of skeletal muscle fibers is mainly determined during the embryonic stage, while the growth and hypertrophy of muscle fibers are achieved after birth through satellite cell proliferation and fusion. The study found that the critical period of skeletal muscle development in the embryonic stage of duck (such as embryonic age of 13 to 19 days) corresponds to specific microRNA and gene expression peaks, indicating a developmental stage-specific gene regulation network. After the shelling, the muscle and adipose tissue of the duck chicks will change significantly with the increase of day age: the growth rate is the fastest before 4 weeks of age, and then the weight gain gradually slows down and matures (Chen and Li, 2024). In this process, endocrine factors such as the growth hormone (GH)-IGF axis play a role, and the epigenetic state of the gene (such as the methylation level of the growth-related gene promoter) is also changing dynamically (Cong et al., 2023). 2.2 Feather formation and periodic changes The feather development of ducks has its own unique rules. Ducklings are covered with down feathers when they come out of their shells, which are mainly used for insulation. In subsequent growth, ducks will undergo a replacement process from down feather to child feather and then to adult feather, which is equivalent to the hair replacement cycle of mammals. Studies have shown that ducklings gradually grow primary flying feathers and body covering feathers within a few weeks after birth, and the primary down feathers are replaced with more functional juvenile feathers for simple flight and stronger insulation (Lu et al., 2024). As sexually mature, ducks also develop reproductive plumes, showing seasonal or gender-different feather morphology and color. Periodic growth and defecation of feathers (feathering) usually occurs 1 to 2 times a year in waterfowls such as ducks and others, and is mostly performed after the breeding season. Feather formation is driven by stem cell proliferation and differentiation within feather follicles (Figure 1). Feather development includes processes such as feather bud formation, feather axis and feather sheet differentiation, keratin deposition, etc., which are precisely controlled by a series of gene regulatory pathways, such as Wnt/β-catenin signal promoting feather primordial formation, BMP signal limiting feather spacing, and Shh signal mediating feather branch branches, etc. Feather development processes are also affected by epigenetic regulation. For example, the chromatin open state of the promoter of specific genes of feather stem cells is closely related to its differentiation potential. The color pattern of feathers also depends on the distribution of melanocytes in the embryonic stage and the expression of related genes, which may be affected by epigenetic factors (such as pigment gene promoter methylation, non-coding RNA regulation, etc.) (Twumasi et al., 2024). Therefore, feather development is a dynamic and complex process with clear stages and periodicity, and behind it involves the exquisite regulation of developmental biology and epigenetics.
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