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.
[48] and to the production of offspring [55,56,87,100],
this technology is still far from being commercially viable.
The major limitation to the diffusion of IVEP in
buffalo is the low number of recruitable oocytes, arising
from peculiarities of the reproductive physiology of the
species, and as such, not easily modifiable.
Another limitation is given by the high susceptibility
of buffalo IVP embryos to cryopreservation,
related in part to their greater lipid content [16] but also
to their poor viability, likely determined by suboptimal in
vitro culture conditions. This results in the overall poor
pregnancy to term recorded following transfer of IVP
cryopreserved embryos (8-25%). However, it is worth
specifying that the development to term is strongly
reduced because of the high incidence of embryonic
mortality occurring between 25 and 50 days; in our recent
experience pregnancy rate was 50% on day 30, to lower
down to 10% pregnancy to term, with the embryo loss
recorded before day 50. At our latitudes during the longday
length period a high incidence of embryonic mortality
is also observed during natural mating, but it increases
further when reproductive biotechnologies, such as AI
and embryo transfer (ET) of in vitro produced embryos
(IVP) are utilized [17]. It has been hypothesized that this
phenomenon is due to both a poor quality of the oocytes
and to the reduced function of corpus luteum (CL), leading
to lower progesterone (P4) secretion [17-19]. The
problem of embryonic mortality is even greater when
IVEP technology is employed because in this case another
factor plays a role, i.e. the poorer viability of in vitro
produced embryos. It is known, in fact, that suboptimal
culture conditions affect all post-implantation events [74].
It is worth reminding that scientific improvement
in this species has been hampered by contingent factors.
The major factor that has delayed scientific advances in
buffalo IVEP is the scarcity of experimental material in
all the countries in which the species is bred, due to either
the heads consistency, the low culling rate and/or the
breeding systems. Furthermore, the economic importance
of the species has only been recently appreciated, and as
a consequence, the first studies of advanced reproductive
strategies in this species date back only to the 1990s.
Finally, the majority of buffaloes is bred in developing
countries where scientists often have to deal with poor
resources and lack of facilities. The scarcity of experimental
material for buffalo, together with the assumption
that the reproductive biology in all ruminants is similar,
led in the early attempts, to use the IVEP system in buffalo
based solely on information acquired in cattle, with the
consequent result of low IVEP efficiency. On the contrary,
it has been demonstrated that improvements in IVEP
are possible through the optimization of each procedural
step, especially when taking into account species-specific
differences, as shown by the higher blastocyst rates
reported over recent years [48].
Therefore, the aim of this review is to report the
major breakthroughs in the OPU and IVP technologies
in buffalo in the past 20 years, the current state of the art
and expected future improvements. The review will be
structured in separate subsections, that will highlight the
most important limitations and progresses achieved in the
different sequential steps of in vitro maturation (IVM),
in vitro fertilization (IVF) and in vitro culture (IVC), as
well as in embryo cryopreservation.
II. OOCYTE SOURCE AND QUALITY
The major intrinsic limitation of IVEP technology
in buffalo lies in the low number of immature oocytes
that can be recovered per donor. With controlled follicular
aspiration of abattoir-collected ovaries, the average
number of total oocytes per ovary varies between 0.7
and 4.3 [10, 27, 63, 111]. In addition, because of the high
incidence of atresia, the mean recovery of good quality
oocytes per ovary is further reduced: 0.4 [63,111], 0.9
[27], 1.76 [102], and 2.4 [51]. In our setting, controlled N
follicular aspiration of abattoir-collected ovaries allows
the retrieval of 4.3 total oocytes [10] and 2.4 good quality
oocytes per ovary on average [51]. The slightly lower
oocyte recovery reported by Indian authors may be due
to differences in breed, older age at slaughter, management
and nutritional status [54], as the plane of nutrition
is known to affect the follicular dynamics [105].
Among factors affecting oocyte recovery, the
ovarian status plays a role, as it has been reported that
the number of oocytes is further decreased when ovaries
have a corpus luteum [84]. Furthermore, results obtained
in OPU trials carried out on buffalo cows at different
days in milk [12,14,15] suggest that the number of follicles
and hence that of the oocytes decrease at increasing
postpartum period (>500 d). Indian authors reported that
the number of COCs is reduced during summer [70],
suggesting an influence of season on the follicular
population. In contrast, no variation in the follicular and
oocyte population has been recorded among seasons in
temperate climate [32].
However, despite small differences, it is
overwhelming evident that the recovery rate in buffalo is
much lower than in cattle, in which 10 good quality oocytes
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