Die Bedeutung der Embryonenqualität im Rahmen des Embryotransfers beim Rind – eine Literaturstudie

The aim of this work was to describe the importance of the
estimation of the quality of cattle embryos in embryo transfer as
well as to discuss the causes of the appearance of the variable
embryo qualities after superovulation and the different
possibilities to assess the embryo quality. After superovulation
there are always variable embryo quality observed. The reasons for
this are versatile. An important, the result of a superovulation
treatment influencing factor, is the donor cow. Both the individual
disposition, the age and as well healthy status and the
stressexposition of the animals are playing an important role. The
ovary reactions are rather essentially influenced by the existence
of a dominant follicle at the moment of introduction of a
superovulation treatment. By removal of dominant follicle the
results can significant be improved. Another important factor is
the sort of a gonadotrophin used for superovulation. The reaction
to a superovulation treatment is not just depending on the
selection of the gonadotroph hormone, but also on the composition
of the preparations, the doses und the way of application. Because
the morphological evaluation of embryo quality is subjected to
subjective influences, it should attach importance to the training
of the evaluating persons, to receive comparable results. The
importance of assessment of embryo quality to select embryos is
considerable. The results of embryo transfer, the pregnancy rates,
are essentially depending on the quality of the transferred
embryos. The survival of embryos after kryopreservation is also
influenced by the embryo quality. Embryo quality can be evaluated
by different approaches: if the selected embryo has to be
transferred, the technique to estimate embryo quality must not be
invasive. In the practice of the embryo transfer embryo quality is
estimated before transfer by gross embryo morphology. However, this
method is a rather subjective possibility for assessment of the
embryo quality. More accurate date can be obtained by the use of
invasive techniques. Metabolic tests to evaluate embryo viability
include measurement of nutrient uptake, energy metabolism and
oxygen uptake. Enzyme leakage and hormone or growth factor
production can also give more details on the quality of embryos.
Techniques which might partially are able to affect the embryo are
the determination of the freezing resistance and vital staining.
With vital staining, membrane integrity, which is critical for
embryo survival, can be assessed by means of fluorescent probes.
The most common staining methods for evaluating embryo quality are
DAPI and FDA. These two fluorescent probes do not alter the embryo,
so that you can still transfer the embryo after these examinations.
Invasive assessment of the embryo quality mostly involves a kind of
fixation or staining of the embryo and so they are not suitable for
the practical use of the embryo transfer. Cytogenetic analysis of
embryos is an important issue for caryotyping. Chromosomal
deviations are known to cause early embryonic mortality in cattle.
Determination of the total cell number and the allocation of these
cells to the inner cell mass (ICM) and trophectoderm (TE) after
differential staining of these cells give more details on the
quality of an embryo.