Abstract :
Successful production of high quality blastocysts depends on the use of a culture system
that ensures the acquisition of developmental competence by the maturing oocyte followed
by an efficient in vitro fertilization. In the present work the effect of FSH and pyruvate in an
EGF containing medium for ovine oocyte maturation prior to insemination with fresh (F)
or frozen–thawed (FT) semen on embryo developmental competence and cryosurvival was
determined. Sheep oocytes were matured in two culture media (M1 and M2, respectively;
M1 = CM + EGF, n = 836 and M2 = CM + EGF + pyruvate + FSH, n = 850) for 22 h and then fertilized
using FT or F spermatozoa (M1 × FT = 371, M2 × FT = 359, M1 × F = 353 and M2 × F = 372,
9 replicates) from Merino rams (n = 3). After embryo culture and evaluation, good quality
blastocysts (grade 1) were vitrified in OPS. Post-thawed embryo integrity, re-expansion
and number of total and viable cells were assessed. Oocyte maturation rates presented no
differences (P > 0.05) between treatments (M1 = 87.0 ± 4.1 and M2 = 86.7 ± 3.9%) as well as
embryo developmental rates either for maturation media or semen status. However, fresh
semen improved blastocyst quality (grade 1 embryos F = 52.5 ± 4.8% and FT = 39.0 ± 4.4%,
P = 0.01). Grade 1 blastocysts presented similar post-thawed integrity and re-expansion
rates. After 3 h of culture, expansion rates were higher (P = 0.05) for M2 × F warmed embryos
(80.0 ± 8.3%) than for M1 × F (54.3 ± 10.4%). Results seem to confirm the existence of a
synergistic effect between FSH, EGF and pyruvate upon cytoplasmic maturation of ovine
oocytes. Moreover, in vitro fertilization by fresh semen clearly improves ovine embryo
developmental competence by enhancing morphological blastocyst quality. The beneficial
effect of M2 on cryosurvival was only observed in embryos derived from fresh semen.
Therefore these combined strategies enhance embryo cryosurvival
