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Fertilization and the Process of Fertilizing
26/12/2007 

    Fertilization is the process of the fuse of a sperm and an ovum then the ovum is the base of organism.
    1. How long will sperm survive in the genital tract of female dog
    The site of fertilization of dog is the ampulla of uterine tube. It needs 15 minutes for sperm arriving oviduct and the fast speed is 30 seconds. The process of the fertilization of dog is very short, and if the sperm and ovum have strong ability on fertilizing, the process of fertilizing can limit to one hour. The sperm can live for 268 hours in genital tract of female dog, keeping its fertilizing ability for 134 hours; however, the vitality of sperm is week as time passed. Otherwise, the time of sperm living in uterus is related with the time of rut recover. When the rut recover begins, the sperm will disappear. Female dog assimilates most of the unfertilized sperms.
    2. How long will ovum can keep fertilization ability
    The ovarian follicle develops 11 days before ovulating, and 2 to 3 days before ovulating, the ovarian follicle grows to maturity. Female dog ovulates after mating for 1 to 2 days, and 80% ovum ovulated after ovulating for 48 hours. The speed of ovulating is affected by the age of female dog that is the young dog ovulates slower than the old and weak dog. Ovum can live for 4 to 8 days in uterine tube, and keep its fertilization ability for 108 hours after ovulating.
    Therefore, female TM can hybridize after rut for 4 to 5 days to avoid the phenomenon of failing pregnant.
    3. Process of fertilizing
    The process of fertilizing includes three stages; sperm penetrate into the corona radiata, clear tape and lecithymen of ovum, and at last, enter into yolk.
    Before fertilizing, a great deal of sperms encircle oocyte, and the sperm perforation release hyaluronidase to dissolve the corona of ovum so sperm can penetrate clear tape. Ovum doesn¡¯t select sperm but find sperm actively. When penetrating into corona radiata, the acrosome of sperm begins to expand and relying on secreting zonallysin, the sperm can penetrate into clear tape. Ordinarily, tens of sperms can penetrate into the gap within the clear tape but only one or several sperms can enter into lecithymen and the ovum is more selective to sperm, new sperms and surplus sperms are prevented to enter yolk. This defense mechanism to prevent more than one sperm enter into yolk is called vitelline block.When sperm enters into yolk, it forms male pronucleus and ovum forms female pronucleus. They move to each other and combine to form zygocyte. This is the end of fertilization and the germ cell is developing.

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