**4. Effect of heat stress on oocyte function and development competence**

The bovine oocytes are extremely compromised of heat stress impact in cattle's [1]. The high temperature affect germinal vesicle (GV) maturation phase of oocyte which shows vulnerability in bovine oocyte. Heat stress affects the developmental competence of germinal vesicles in oocytes of Holstein cattle's, as evidenced a decrease in consequent embryonic development [1] demonstrated that exposing. The Holstein to environmental chamber at heat stressed are 42°C for 10 hours for done successfully. The number of Normal embryos was reduced during oocyte maturation as compared to control (24°c) [1]. The three successive oestrus cycles can be required for an oocyte to recover from heat stress and then recover its oocyte competency in the following for season [9]. Over a long period of time, heat stress can cause major impact on ovarian pool of oocytes. The impact might also disturbed cow fertility and harmed even in the autumn (when there is no ambient thermal stress). As demonstrated by the oocyte competence stability and pregnancy in warmth weather which follow in winter. The hyperthermia of maternal half of concentration of ovarian follicles but does not affect the follicular pool. The oocyte maturation failure can take a variety of forms when exposed to heat stress. It interferes with the biosynthesis of steroid hormones, which are responsible in oocyte maturation regulation mechanisms [9].
