| Summary: | The purpose of this study was to evaluate the effects of royal jelly (RJ) on the morphology of the reproductive tract, egg production, and blood biochemical indices of aged laying hens. In total, 120 Lohman Brown laying hens at week 58 of age were randomly assigned into three equal groups. Pure RJ was dissolved in distilled water and injected subcutaneously as follows: the first treatment (R<sub>1</sub>; 100 mg RJ kg<sup>−1</sup>); the second treatment (R<sub>2</sub>; 200 mg RJ kg<sup>−1</sup>); the control treatment (CON; 1 mL distilled water). Both RJ-treated groups exhibited a significantly higher number of large yellow follicles (LYFs), small yellow follicles (SYFs), and large white follicles (LWFs) (<i>p</i> ˂ 0.05). Furthermore, RJ treatment significantly increased the diameter and weight of the F1 follicles. However, only the R2 group exhibited significantly greater ovary and uterus weights. RJ treatment did not affect the percentage of oviduct and weight of ovarian stroma. In addition, RJ increased the hen–day egg production rate compared with the CON group; however, only the R<sub>2</sub> group showed greater egg weight (<i>p</i> = 0.032). RJ treatment also improved the albumen height, Haugh units, and yolk index. The administration of RJ significantly decreased the serum glucose, but increased the levels of serum albumen and cholesterol. In conclusion, RJ treatment may improve the morphology of the reproductive tract (including follicular growth and oviduct morphology), egg production rate, and internal egg quality traits of aged laying hens.
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