Abstract: 【Objective】 The purpose of this study was to explore the maturation characteristics of raccoon dog oocytes,and to provide a basis for the in vitro maturation culture of raccoon dog oocytes and to select high-quality mature oocytes,so as to improve the in vitro fertilization efficiency of raccoon dog.【Method】 Fresh ovaries from 1 to 3 years old female raccoon dogs at reproductive stage were collected to prepare light and electron microscope samples to observe the changes of organelles during oocyte maturation of raccoon dog. X-ray microanalysis was used to explore the relationship between the changes of chemical elements in plasma membrane and maturation of oocyte.【Result】 The maturation and development of raccoon dog oocytes could be divided into 8 stages according to the layer number of granulosa cells,the diameter of follicles,the size of oocytes and the changes of the zona pellucida.Raccoon dog oocytes were surrounded by granulosa cells in the early developmental stage (stages Ⅰ to Ⅳ),with the gradual appearance of the zona pellucida and the follicular cavity,the chromatin in the germinal vesicles became more and more compact.With the maturation and development of oocytes (stages Ⅴ to Ⅶ),cortical granules and microvilli appeared and the number of organelles such as Golgi complex,mitochondria increased significantly and they gradually migrated to the cortex,while mitochondria and lipid droplets experienced morphologic variation.When the oocyte grew mature (stage Ⅷ),the Golgi complex and the rough endoplasmic reticulum disappeared,and the cortical granules were arranged under the plasmalemma.After ovulation,the nucleolus became compact.The contents of sodium,chloride and sulfur in oocyte plasma membrane decreased with the increase of follicular cavity.The contents of sodium,chlorine and sulfur in oocyte plasma membrane in stage Ⅴ were significantly higher than those in stage Ⅶ (P＜0.05),and the relative content of calcium was significantly lower than that of stage Ⅵ and Ⅶ oocytes (P＜0.05).Potassium showed a low-high-low variation,and the content of potassium in oocyte plasma membrane in stage Ⅵ was significantly higher than that of stage Ⅴ and Ⅵ oocytes (P＜0.05).【Conclusion】 After the raccoon dog oocytes developed to stage Ⅴ,the type and number of organelles increased,the plasma membrane chemical elements changed,and oocyte membrane potential was depolarized,and the oocytes began to enter the mature stage.At this time,the oocytes had the ability to mature in vitro.

Key words: raccoon dog oocyte; maturation development; organelles; chemical elements