Abstract: 【Objective】 This experiment was aimed to investigate the effects of adding different doses of epidermal growth factor (EGF) to the diet on the morphology,hormone levels,and the expression of apoptotic factors of ovaries in laying hens,so as to provide a theoretical basis for elucidating the role of EGF in promoting the growth and development of ovaries in laying hens.【Method】 Two hundred and forty healthy,high-producing White Leghorn laying hens aged 260 days with similar body weights were selected and randomly divided into four treatment groups,with five replicates per group and twelve hens per replicate.The laying hens in control group (Con) were fed a basal diet without EGF supplementation,while laying hens in three experimental groups (LG,MG and HG) were fed basal diets supplemented with 200,400 and 800 mg/kg EGF,respectively.The advanced experiment period lasted for 7 days,and the formal experimental period lasted for 42 days.From each replicate,two laying hens were selected for blood collection and sample harvesting.The weights of ovaries,oviducts and follicles were measured,as well as the number of follicle grading was counted.The concentrations of luteinizing hormone (LH),follicle-stimulating hormone (FSH),estradiol (E₂) and progesterone (P₄) in serum were assayed.The expression of apoptotic factors Bcl-2 and Caspase-3 in ovaries were evaluated using Real-time quantitative PCR and Western blotting,respectively.【Result】 Compared with Con group，①The addition of different doses of EGF to the diet had significant effects on ovarian weight,ovarian index and the number of white follicles in laying hens (P＜0.05).However,there were no significant morphological changes observed in ovaries among the different groups.②The levels of LH,FSH and E₂ in serum of laying hens in LG,MG and HG groups were significantly increased (P＜0.05),the level of P₄ in serum of laying hens in LG and MG groups were also significantly increased (P＜0.05).③The relative expression of Bcl-2 gene in ovaries of laying hens in LG and MG groups was significantly increased (P＜0.05),the relative expression of Bcl-2 protein in ovaries of laying hens in LG,MG and HG groups was also significantly increased (P＜0.05).Conversely,the relative expression of Caspase-3 gene in ovaries of laying hens in LG and MG groups was significantly decreased (P＜0.05),the relative expression of Caspase-3 protein in ovaries of laying hens in MG and HG groups was significantly decreased (P＜0.05).【Conclusion】 Under the conditions of this experiment,the addition of different doses of EGF to the diet promoted the secretion of ovarian reproductive hormones and follicular development to a certain extent,effectively inhibited cell apoptosis and thereby improved the production performance of laying hens.The recommended addition amount of EGF in diet for high-producing White Leghorn laying hens was 400 mg/kg.

Key words: epidermal growth factor; laying hens; reproductive hormones; ovary; apoptosis