Effects of cattle oocyte quality on pronuclear formation and subsequent embryo development

The effect of oocyte quality on the pronuclear (pn) forma tion and subsequent development of embryos in local cattle was studied. cattle oocytes matured and fertilized in vitro were unable to acquire developmental competence unle ss matured with intact cumulus cells. the presence of cumulus cell s promoted normal fert ilization with proper pronuclear (2pn) form ation, in the pre sent stud y, the characteri stics and quality of cumulus-oocyte-complexes influenced the pronuclear formation but not subsequent cleavage and blastocyst form ation . the oocytes from grade a , grade b and grade b' were capable of fertilization and development unde r in vitro cond itions. fertilization rates were significantly different (p <0.05 ) among the three grades of oocytes. grade a oocytes had the highest fertiliz ation rates (55 .0%) follow ed by grade b (44 .0% ) and grade b' (30 .2%). incidence of polysperm y (>2pn) was 18.8% in grade b' oocytes but none in grade s a and b oocytes. the mean percentages of cleavage and blastocyst rates were not significant (p >0.05) in grades a , band b' (71.6, 74 .9 and 73.6%, respectively, and 10.5, 10.4 and 7.4 %, respectively). in conclusion , this study indic ated that the compactne ss of cumulus cells surrounding the ooc ytes influenced the pronuclear form ation of cattle oocy tes but not clea vage and blastocyst rates.