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.
are obtained on average per ovary [53]. Similarly, when
OPU is carried out the number of oocytes collected per
donor is much lower in buffalo than in cattle (4.5 vs
approximately 10 respectively [41]).
This is not surprising if we consider some
physiological features, peculiar of this species: 1) lower
number of primordial follicles in the buffalo ovary, varying
from 10,000 to 19,000 [26,103] compared with 150,000
in cattle [39]; 2) lower number of antral follicles
throughout the whole estrous cycle [61]; 3) high incidence
of follicular atresia, i.e., 82% [90] or 92% [91] and 4)
smaller and lighter gonad compared with that of cattle
(2.5 cm vs. 3.7 cm of length; 3.9 g vs. 8.5 g of weight
respectively; [116]). It results that this limitation is currently
the major impediment for the diffusion of IVEP in the
field, arising from physiological peculiarities of the species,
and as such, it is not easy to improve.
However, as previously stated, it is possible to
increase the number of competent oocytes by operating
the selection of the donors on the basis of their follicular
population [44,100]. An earlier trial carried out on deep
anoestrus buffalos demonstrated that it is possible to
increase the number of aspirated follicles (6.75 vs 4.17),
recovered oocytes (3.00 vs 1.33), and the oocyte quality
(55.6% vs 31.3%) by priming OPU donors with FSH-P
[11]. However, the oocyte yield was low also in the
primed-donors, because of the poor starting ovarian status.
More recently, it has been shown that rBST pretreatment
of buffalo donors [100] promotes follicular growth (12.2
vs 8.7 total follicles punctured) and tends to increase the
number of oocyte recovered per session (5.2 vs. 4.1; P
= 0.07), as well as the percentage of good quality oocytes
(48.8% vs. 40.6%; P = 0.07). Nevertheless, in agreement
with results previously reported in cattle [9,112], the
treatment failed to increase the blastocyst production rate
and the number of blastocyst produced per buffalo per
session. Similar results were also obtained in a subsequent
trial in which the rbST treatment was tested on donors
undergone OPU once per week [2]. Therefore, these
approaches are successful to increase the number of
gametes but only to a limited extend. Furthermore, it is
worth underlining that one of the advantages of OPU
over MOET is exactly the possibility to avoid hormonal
treatment of the donors and subsequent side effects.
However, for a complete review it is worth to
cite that recently Baruselli et al. [2] reported a number
of oocytes recovered per buffalo per OPU session much
higher than the average values reported in literature, in a
trial in which the interval between sessions was extended
to one week (8.5 and 6.1 total and viable oocytes,
respectively) and two weeks (10 and 7.2 total and viable
oocytes, respectively). It is known that many factors may
affect the recovery rate, such as the tractability of the
animals, the skill of the operator, the efficiency of the
aspiration set, etc but the extraordinary high number of
follicles observed is difficult to explain as this may only
depend on the donors. We may speculate that the evident
difference in the follicular population may be due to the
genetics of the animal, the age (heifers vs adults), the
type of breeding and environment, as well as the longer
interval between sessions. The latter factor may account
for both the greater number of follicles and the lower
developmental competence of the oocytes, indicated by
the poor blastocyst rate (9 %); indeed, it is known that an
extension of the interval increases the number of follicles
but also the heterogeneity of the oocyte source, as the
phenomena of dominance and atresia in this case occur.
Oocyte quality, that is known to be a major factor
affecting the IVEP efficiency in most species, plays a
determining role in buffalo, further decreasing the
availability of the oocytes suitable for IVEP. Indeed, it is
possible to increase the IVEP efficiency by selecting the
oocytes but this in turn reduces the number of oocytes
that can be processed, that is the real limiting factor in
this species.
It is known that the oocyte morphology can
reliably predict the gamete developmental competence;
according to our classification, a progressive decrease
of efficiency is recorded from Grade A to Grade D
oocytes [86], with Grade A and B considered suitable for
IVEP. It is worth pointing out that the percentage of good
quality oocytes (Grade A and B), is lower in this species
compared to others, not exceeding, in our experience 50
% of the total oocytes recovered. An analysis of the data
collected over a 4-years period in our lab showed that
from a total number of 35.286 abattoir-derived oocytes
(over 158 replicates) 47.8% were Grade A + B, 6.2 %
were Grade C and 46.7 % were unsuitable for IVEP
(Gasparrini, personal communication, 2010). A recent trial
has shown an even lower proportion of good quality
oocytes (33.7 % of Grade A+B), together with a higher
incidence (37.9 %) of Grade C [78].
In alternative to morphological criteria, the non
invasive brilliant cresyl blue (BCB) staining before IVM
can be used to select developmentally competent abattoirderived
oocytes [65]. This method allows the selection
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