EFFECT OF SEASONS ON OOCYTES QUALITY AND IN VITRO MATURATION RATE IN BUFFALO

Heat stress (HS) during summer was found to impair the reproductive potentials in buffalo. The present study was designed to evaluate the effect of seasons on: a) Number of the ovarian follicles and number and quality of their enclosing oocytes, b) Cumulus cell expansion and nuclear maturation rates of in vitro matured buffalo oocytes In experiment 1: During whole
year, buffalo ovaries were collected and the number of ovarian follicles was counted, oocytes were recovered/ovary and classified according to their morphology into 4 Grades. In Experiment 2: Grade 1 and 2 cumulus-oocyte-complexes (COCs) were in vitro matured (IVM), cumulus-cell expansion and nuclear maturation were determined. In Experiment 3:Mitochondrial activities in non-matured and matured buffalo oocytes were assayed using Mito-Tracker Red stain. Results showed that the number of ovarian follicles and the quality of oocytes were diminished in summer. Also, summer season significantly (P<0.05) decreased cumulus-cell expansion and nuclear maturation of IVM buffalo oocytes. Matured buffalo expressed clustering homogenous distribution, while, non-matured ones showed polarized mitochondrial distribution.