Abstract :
The aim of this study was to test the effect of insulin–transferrin–selenium (ITS), l-ascorbic
acid (AA) and different hormone concentrations at IVM on blastocyst development, MPF
activity and ATP content in lamb oocytes. In this study we used three maturation media:
conventional IVM medium (CM), growth medium (GM: CM + ITS + AA and low level of hormones)
and modified CM (MM: CM + ITS + AA and conventional hormone concentration).
Cumulus–oocyte complexes (COCs) were classified into two categories according to results
from BCB staining: fully grown oocytes or BCB+ and growing oocytes or BCB−. A group
of control oocytes (not BCB stained), BCB+ and BCB− were matured (IVM) for 24 h in CM
(Treatments A, B and C, respectively). Also, BCB− oocytes were matured in four treatment
groups: Treatment D: 12 h in GM plus 12 h in CM; Treatment E: 24 h in GM; Treatment F:
12 h in GM plus 12 h in MM; Treatment G: 24 h in MM. After IVM, oocytes were fertilized
and cultured for 8 days and blastocyst development was assessed. Before and after IVM, a
sample of each oocyte group was taken to evaluate MPF and ATP content. The BCB+ oocytes
produced the highest blastocyst (13.3%) yield. BCB− oocytes did not show any statistically
significant differences in blastocysts between treatments, D (5.9%), E (7.2%), F (2.9%) and
G (3.9%) compared to Treatment C (4%). Results of MPF activity and ATP content assessed
before and after IVM showed an increase in all oocytes (P < 0.001) after 24 h of IVM compared
to immature oocytes (0 h). No differences were observed among treatment groups.
In conclusion, BCB− oocytes were unable to improve embryo development in any of the
treatments tested in this study. Embryo development of BCB+ oocytes was significantly
higher than BCB− oocytes.
