Morphometric Assessment of the Bovine Ovary for in vitro Matured Oocyte Quality to Determine Developmental Competence

Abstract

Background: Embryo production in vitro requires three steps: in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC). The first step in the in vitro maturation of oocytes is germinal vesicle breakdown (GVBD), followed by completion of the 1st meiotic division and formation of the 1st polar body. These parameters are critical during ovary and oocyte selection. This study aimed to evaluate bovine ovary and oocyte collection for IVM. Methods: Ovaries collected from cows in a 0.9% NaCl saline solution at the central slaughterhouse were divided into two normal and abnormal ovaries according to their morphological appearance. The morphometric dimensions of bovine ovaries, such as weight and deamination (length, width and volume), were recorded. The oocyte was extruded and its deamination occurred before and after culture in maturation medium. Result: The mean ovary weight, volume, length and width were not significantly different between the two ovary types. Additionally, the dominant and subordinate follicle diameters in both ovary types showed no significant differences. Furthermore, the oocyte number per ovary of the normal and abnormal oocytes showed no significant differences. The mean cumulus oocyte complex before maturation showed no significant difference (52.73±7.23 mm for the normal ovary vs. 43.015±5.41 mm for the abnormal ovary). However, after maturation, a highly significant difference was found (P less than 0.001) between the normal ovaries before and after maturation (178.10±15.36 µm) and abnormal ovaries (10.45±7.99 µm). Additionally, data analysis of oocytes with or without 1st polar bodies revealed a highly significant difference (P less than 0.001) between oocytes of the normal ovary with (32.15±4.19) and without (10.95±1.59) 1st polar bodies and oocytes of the abnormal ovary with (7.0±078) and without 1st polar bodies (3.3±0.32). Thus, the critical point at which the normal ovary produces better in vitro matured follicles with good oocyte quality and produces the 1st polar body determines developmental competence. Therefore, the best selection of normal ovaries will enhance in vitro maturation for subsequent experiments, such as in vitro fertilization or cloning and in vitro embryo development.