Effect of Cumulus Oocyte Complex Morphology on in Vitro Maturation of Bovine Oocytes*

An experimental design was framed to analyse the effect of cumulus oocyte complex (COC) morphology on in vitro maturation of bovine oocytes. Slaughter house derived bovine ovaries from South Indian breeds and crossbred cattle of Kerala were subjected to three retrieval methods to yield different quality grades of oocytes. Based on the number of layers of cumulus cells and ooplasm character, the oocytes were graded into four classes from A to D. Each grade of oocytes obtained through different retrieval methods were incubated at 38.5°C with 5% carbondioxide tension and maximum humidity for 24 h in TCM-199 medium supplemented with LH, FSH, estradiol, pyruvate and foetal calf serum. Maturation changes were assessed by cumulus expansion, formation of M II plates and polar body extrusion. Oocytes with more than three layers of cumulus cells exhibited maximum maturation rate irrespective of their retrieval method. The experiments revealed that COC morphology has a very significant role in maturation of bovine oocytes.