Semester

Fall

Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Robert A. Dailey.

Abstract

In mammals, ovarian follicles begin as primordial follicles. Over time these follicles are gradually activated and begin growth. As they proceed, granulosal and thecal cells are acquired. Eventually, the follicles become dependent on FSH for survival. Two or three times each cycle, a transient increase in FSH allows a cohort of follicles, including the follicle that will ovulate, to continue growing. However, these follicles secrete inhibin and estradiol, which suppress FSH secretion. Eventually, all the follicles of the cohort undergo atresia due to the declining concentrations of FSH, except for the follicle which has the potential to ovulate. This follicle survives the decline in FSH because the granulosal cells of that follicle develop LH receptors that allow stimulation to keep the follicle healthy. The concentrations of estrogen and free insulin-like growth factor I are different in the selected follicles compared to the follicles that underwent atresia in the cohort of follicles. However, because the ovulatory follicle cannot be identified until after it is selected, it is difficult to study the initial changes causing selection. One phenomenon from which insights to selection can be gained is compensatory hypertrophy, which is the ability of an animal to maintain the same ovulation rate after removal of one ovary. This compensation occurs at the next estrus, unless the unilateral-ovariectomy is carried out at the end of the cycle. Therefore, the present study determined the fate of the subordinate follicles following removal of the selected follicle at different stages of the estrous cycle of the cow. Results indicated that if the dominant follicle of a second wave and the CL were removed at day 13 post estrus, the largest subordinate follicle remaining became dominant. However, all treatments later in the cycle resulted in regression of the remaining follicles and emergence of a new wave of follicles before ovulation.

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