International Journal of Molecular Zoology, 2025, Vol.15, No.1, 10-19 http://animalscipublisher.com/index.php/ijmz 15 Individuals with low FE in laying hens and local hens often showed upregulation of immune and inflammatory pathways (Aggrey et al., 2014; Yang et al., 2020). 6.2 Line-specific biomarkers and selection potential Sinpru et al. (2021) found that in slow-growing Korat chickens, differentially expressed genes in the jejunum are enriched in immune response, glutathione metabolism and fat metabolism pathways, and these genes may become breeding targets for improving FE. The research results of Ye et al. (2024) demonstrated that genome-wide association studies (GWAS) identified some important SNPS and candidate genes related to FE, such as EXOC4, FBRSL1, MAT2B, and CMPK1, in Qingyuan free-form chickens. These genes support genetic improvement using molecular markers. In the multi-tissue transcriptome analysis of hybrid chickens, specific circular RNAs (circRNA) in the hypothalamus and liver were also identified. These non-additive circRNA may be used to predict the hybrid dominance of RFI and FE (Yuan et al., 2024). 6.3 Implications for precision nutrition and breeding Understanding the differences in metabolism and regulatory pathways among different chicken breeds is helpful for formulating more targeted nutritional intervention and genetic improvement plans. In broilers, it can enhance mitochondrial function and reduce the production of reactive oxygen species (ROS). In native chickens and slow-growing breeds, it can regulate immune and metabolic pathways, thereby increasing FE and reducing costs (Yang et al., 2020; Sinpru et al., 2021; Wang et al., 2022). Integrating the biomarkers discovered in the transcriptome and metabolome into the breeding system is beneficial for identifying chickens with better FE. It can not only promote the sustainable development of poultry farming but also enhance the economic benefits of multi-breed farming (Karimi et al., 2021; Ye et al., 2024; Yuan et al., 2024). 7 Environmental and Nutritional Modulation of Feed Efficiency (FE) 7.1 Effects of diet composition and feed additives Adjusting the ratios of amino acids, energy and crude protein, especially increasing the ratio of arginine and lysine above the recommended value, is helpful for regulating energy and protein metabolism and thereby improving FE. The research conducted by Zampiga et al. (2021) demonstrated that some feed additives such as crystalline amino acids, proteases, and phytase can help chickens make better use of nutrients, reduce environmental pollution, and support more efficient intensive farming. Plant-based additives such as essential oils and plant extracts (PFAs) can also improve FE. They can regulate metabolic pathways, increase muscle protein synthesis, and inhibit liver fat formation (Pirgozliev et al., 2019; Flees et al., 2020), these additives can also regulate the immune system and improve nutrient retention, promoting the growth performance of chickens (Pirgozliev et al., 2019). Choi et al. (2023) and Bernard et al. (2024) found that adjusting the gut microbiota with prebiotics, probiotics and exogenous enzymes can also enhance nutrient absorption, improve body composition regulation and increase FE. 7.2 Thermal stress and housing conditions High temperature is a common environmental stress in poultry farming. It can lead to slower growth of chickens, weakened immunity, and even death, reducing feed efficiency (FE). To cope with heat stress, it is necessary to adopt some nutritional strategies, such as providing feed with high digestibility and high nutritional density, increasing the fat content in the feed, balancing the proportion of amino acids, and supplementing vitamins, minerals and antioxidants. Early research by Mujahid (2011) indicated that these practices were helpful in reducing heat production, alleviating oxidative stress, avoiding energy waste, and enabling chickens to maintain good FE even at high temperatures. Improving ventilation and controlling the stocking density, these feeding conditions can be combined with nutritional measures to enhance the chicken flock's adaptability to high temperatures and help increase feed utilization. 7.3 Epigenetic modifications and long-term adaptation Long-term environmental and nutritional regulation can affect gene expression through epigenetic mechanisms, influencing the metabolism, immunity and growth of chickens. The research by Wen et al. (2021) and Bernard et al. (2024) found that the gene expression profiles of chickens with different genotypes were also different under
RkJQdWJsaXNoZXIy MjQ4ODYzNA==