Developmental competence of bovine oocytes: follicular status and ultrasound image characteristics
Abstract
This thesis investigates the relationship between the physiological phase of
follicles in cattle, their echotexture attributes and the developmental competence of the
oocytes that they contain. This study also investigates the local influence of ovarian
structures (CL and dominant follicle) on developmental competence of oocytes and
follicular echotexture. The drive behind this work was to improve the understanding of
ovarian function in this species for the purpose of refining the techniques of follicle
manipulation, and to determine ultrasound image characteristics useful to the
development of diagnostic and prognostic tools for use in cattle and other species,
including humans.
After stimulating the emergence of a new ovarian follicular wave in cows,
images of dominant and subordinate follicles were digitalized at Days 2, 3, 5 and 7 of
the follicular wave. Cumulus oocyte complexes from the same ovaries were collected
from subordinate follicles ≥3 mm and underwent in vitro embryo production to the
blastocyst stage.
Image analysis revealed differences in echotexture between dominant and
subordinate follicles among Days 2 to 7 of the follicular wave. Follicles at Day 7 of the
wave displayed consistently lower (P < 0.05) values of image attributes in peripheral
antrum, follicular wall and perifollicular stroma. Oocytes collected on this day
displayed low developmental competence. The proportion of oocytes that developed to
the blastocyst stage was higher (P