2011 (SBTE) 25th Annual Meeting Proceedings - International ...

B. Gasparrini. 2011. Ovum pick-up and in vitro embryo production in buffalo species: an update.................................................................
jjjjjjjjjjj Acta Scientiae Veterinariae. 39(Suppl 1): s317 - s335.
of a slightly higher percentage of competent oocytes
(57%), without improving, though, the average blastocyst
yields.
The oocyte quality may be affected by several
factors, such as the aspiration pressure during collection,
the source of gametes, the time between collection and
processing, the temperature during transportation, season,
etc.
In our experience, the oocyte morphology varies
with the source of gametes, with an apparent worse
quality of OPU-derived oocytes, characterized by fewer
layers of granulosa cells, compared to abattoir-derived
ones. A different distribution of COCs classes in relation
to the oocyte source was also recorded in cattle, with a
higher incidence of better quality oocytes for abattoirderived
compared to OPU-derived COCs [76]. As this
difference was not due to the OPU equipment or to the
collection medium, it was hypothesized that, due to a postmortem
effect, the COCs becomes less tightly connected
to the follicle wall and therefore are collected with a more
complete morphology. This is even more likely to occur
in buffalo because of the poor adhesion of cumulus cells
[44]. This feature led us to speculate that also technical
factors during OPU, such as the length of the needle, as
well as that of the line connected to the suction unit, may
result in a greater loss of granulosa cells in buffalo oocytes
and, hence in an underestimated evaluation of their quality.
In fact, in contrast to what reported in cattle [76],
despite their worse morphological appearance, OPUderived
buffalo oocytes have a higher developmental
competence compared to abattoir-derived ones [86]. Similar
results have been obtained by Indian authors who
reported both higher blastocyst yields (30.6±4.3 vs
18.5±1.8) and higher blastocyst hatching rates (52.8±4.2
versus 40.2±4.4) following embryo vitrification from
OPU-derived compared to abattoir-derived buffalo
oocytes [66].
The improved embryo yield may be accounted
for by the OPU-induced modification of the follicular
dynamics; resetting the follicular population twice weekly
results in increased follicular wave frequency and, hence
in the aspiration of follicles before they become atretic,
with an improved oocyte “quality”. On the contrary, an
heterogeneous oocyte population is recovered from pooled
ovaries of slaughtered buffaloes. In addition, it is worth
reminding that buffaloes are usually slaughtered when
they are old and/or hypo fertile. It has been suggested
that the better embryo yields recorded in cattle for
slaughterhouse compared to OPU-derived oocytes are
due to early atresia occurring in the post-mortem which
positively affects oocyte developmental competence [3].
This does not seem to be the case in buffalo, suggesting
that further studies are needed to elucidate the occurrence
of atresia and its effect on the oocyte.
It has been speculated that the better
developmental competence of OPU-derived vs abattoirderived
oocytes is related to the shorter exposure to
environmental stress. Indeed, abattoir-derived oocytes
spend a longer time between excision of ovaries from
the peritoneal cavity and laboratory processing and are
probably affected by cellular damages due to autolytic
processes, especially when they reside in excised ovaries
for prolonged periods.
Furthermore, when OPU is carried out in the
field, i.e. in farms distant from the laboratory, a significant
improvement of blastocyst yield can be achieved by
reducing the time between oocyte collection and their
maturation. In these situations, an increased efficiency is
recorded with oocytes searched directly in the farm and
immediately transferred in a hepes-buffered in vitro
maturation (IVM) medium in a portable incubator,
compared with those searched in the laboratory, after
many hours of their permanence in the follicular fluid N
(Gasparrini, personal communication, 2006).
The oocyte competence also depends on the
morphofunctional state of ovaries, with an improved
development recorded with oocytes recovered from
ovaries bearing either a corpus hemorragicum or a CL,
in the absence of a dominant follicle [68]. Furthermore,
when a dominant follicle and a CL are present on the
ovary, cleavage rate and transferable embryo yield are
higher when oocytes are collected from the dominant
follicle compared to the largest subordinate and
subordinate follicles.
Buffalo oocytes are very sensitive to shock
temperature so it is important to monitor the temperature
carefully during collection as fluctuations can easily occur.
When OPU is carried out temperature is controlled by
holding the collection tubes in suitable warm boxes. When
abattoir-derived oocytes are utilized for in vitro embryo
production, the ovaries are usually kept in physiological
saline, under controlled temperature (30-37°C), during
collection and transportation to the laboratory. It has been
recently observed that oocyte developmental competence,
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