Assistierte Reproduktion beim Pferd

In the mare, the practical use of assisted reproduction techniques has been very limited so far. Embryo transfer is used only in a few countries to a low extent. The main reason for this situation is that there is no practical method available for superovulation in the mare. The majority of equine embryos are therefore collected from spontaneously ovulating mares. Synchronisation of the oestrous cycle of the donor and recipient mare before transfer is of major importance. In synchronized recipients, ovulation should occur one day before to three days after the donor mare's ovulation. Ovariectomized, hormone-treated mares have also been used as embryo recipients. In young, fertile mares embryo recovery rates up to 90 % have been reported. Embryo recovery rates for older, infertile mares are only between 20 to 40 %. Embryo recovery is generally performed nonsurgically by transvaginal flushing of the uterus. Nonsurgical recovery of embryos is not possible before day 6 post ovulation. Equine embryos are transferred by surgical flank incision or by nonsurgical, transvaginal transfer. Surgical transfer is mainly used in commercial embryo transfer programs with pregnancy rates up to 80%. The advantage of nonsurgical transfer is the noninvasive technique and the low costs, but results vary tremendously. Cooled, transported embryos offer great advantages in the management of transfer programs. Cooling for 24 to 30 hours does not seem to impair the viability of embryos. Conventional methods of cryopreservation or vitrification can be used for long term storage of equine embryos. Smaller embryos withstand cryopreservation better than large embryos. Micromanipulation of equine embryos can be used to produce monozygotic twins and for embryo sexing. The efficiency of embryo production by extracorporal fertilization in the horse is very low so far. Equine oocytes can be recovered by one of four methods: surgically, by transcutaneous flank puncture, by transvaginal aspiration or by aspirating, scraping or rupturing follicles of slaughterhouse ovaries. Different culture media can be used for in vitro oocyte maturation. After 30 hours of incubation in TCM 199, the maturation rate of equine oocytes to metaphase II is up to 80 % . In vivo fertilization of oocytes can be achieved by surgical transfer into the oviduct or follicles of inseminated recipient mares. The procedure of gamete intrafallopian tube transfer (GIFT) involves transfer of oocytes and spermatozoa into the oviduct of a recipient mare. Since only low sperm numbers are required, GIFT can be used for subfertile stallions, frozen-thawed semen and sexed spermatozoa. Conventional methods or vitrification can be applied for the cryopreservation of equine oocytes. Maturation rates in vitro are lower for frozen-thawed than for fresh oocytes but results of in vitro fertilization rates are comparable. In contrast, embryonic development rates of frozen-thawed oocytes seem to be affected by cryopreservation. In vitro fertilization of matured oocytes can be performed by co-incubation of oocytes and spermatozoa or by assisted fertilization techniques such as mechanical manipulation of the zona pellucida, zona drilling or intracytoplasmic sperm injection (ICSI). Fertilization rates with conventional methods are low (0-25 %), whereas fertilization rates up to 52% are reported with ICSI. Viable offspring has been produced with both techniques. Fertilized oocytes can be cultured to the stage of morula or blastocyst in vivo or in vitro. Co-culture with somatic cells seems to be important for embryonic development in vitro. Live foals have already been produced using in vitro cultured embryos, which developed from ICSI of in vitro matured oocytes.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Ludwig-Maximilians-Universität

Year

2003

Author dc:creator

• Koelle, Nina

Repository record source_url

https://edoc.ub.uni-muenchen.de/1155/

OAI identifier oai:identifier

oai:edoc.ub.uni-muenchen.de:1155